Vulnerability-Lookup

CVE-2026-63895 (GCVE-0-2026-63895)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-07-19 14:55

Title

usb: gadget: f_fs: copy only received bytes on short ep0 read

Summary

In the Linux kernel, the following vulnerability has been resolved: usb: gadget: f_fs: copy only received bytes on short ep0 read ffs_ep0_read() allocates its control-OUT data buffer with kmalloc() (not kzalloc) at the Length value from the Setup packet, then copies that full len to userspace regardless of how many bytes were actually received: data = kmalloc(len, GFP_KERNEL); ... ret = __ffs_ep0_queue_wait(ffs, data, len); if ((ret > 0) && (copy_to_user(buf, data, len))) ret = -EFAULT; __ffs_ep0_queue_wait() returns req->actual, which on a short control OUT transfer is strictly less than len. The copy_to_user() call still copies len bytes, so on a short OUT the last (len - ret) bytes of the kmalloc() buffer -- uninitialised slab residue -- are delivered to the FunctionFS daemon. Short ep0 OUT completions are specified USB control-transfer behavior and are produced by in-tree UDCs: * dwc2 continues on req->actual < req->length for ep0 DATA OUT (short-not-ok is the only ep0-OUT stall path). * aspeed_udc ends ep0 OUT on rx_len < ep->ep.maxpacket. * renesas_usbf logs "ep0 short packet" and completes the request. * dwc3 stalls on short IN but not on short OUT. A short ep0 OUT is therefore not evidence of a broken UDC; it is a normal condition f_fs has to cope with. The sibling gadgetfs implementation in drivers/usb/gadget/legacy/inode.c already does this correctly via min(len, dev->req->actual) before copy_to_user(). This patch brings f_fs.c to the same safe pattern rather than trimming at a defensive layer. The bug is reached from the FunctionFS device node, which in real deployments is owned by the privileged gadget daemon (adbd, UMS, composite gadget services, etc.); it is not reachable from unprivileged userspace. Linux host stacks normally reject short-wLength control OUTs before they reach the gadget, so reproducing this required a build that bypasses that host-side check. With the bypass in place, a 1-byte payload on a 64-byte Setup produces 63 bytes of non-canary slab residue in the daemon's read buffer. Fix by copying only ret (actually received) bytes to userspace.

Severity

No CVSS data available.

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 6843 records in the last 180 days details

References

7 references

URL	Tags
https://git.kernel.org/stable/c/90ccf5fb63243fae1…
https://git.kernel.org/stable/c/af32dbb2ca0b3d092…
https://git.kernel.org/stable/c/e835bf9a055f71874…
https://git.kernel.org/stable/c/88874a19b2b093bfa…
https://git.kernel.org/stable/c/607730a414773a7cb…
https://git.kernel.org/stable/c/23c1f7deb9dd8447e…
https://git.kernel.org/stable/c/4e036c10e7f4df5d9…

Impacted products

2 products

Vendor	Product	Version	CPE status
Linux	Linux	Affected: ddf8abd2599491cbad959c700b90ba72a5dce8d0 , < 90ccf5fb63243fae1b4b3200f3310500500ecf2e (git) Affected: ddf8abd2599491cbad959c700b90ba72a5dce8d0 , < af32dbb2ca0b3d09271ab718d13857a457fa16f2 (git) Affected: ddf8abd2599491cbad959c700b90ba72a5dce8d0 , < e835bf9a055f71874065a40780ca5560b7df8b33 (git) Affected: ddf8abd2599491cbad959c700b90ba72a5dce8d0 , < 88874a19b2b093bfaaa1c0090fa536c44da8c08b (git) Affected: ddf8abd2599491cbad959c700b90ba72a5dce8d0 , < 607730a414773a7cbe3037a64a6c64e72689ff5e (git) Affected: ddf8abd2599491cbad959c700b90ba72a5dce8d0 , < 23c1f7deb9dd8447ecde749850676302aa1e2bd3 (git) Affected: ddf8abd2599491cbad959c700b90ba72a5dce8d0 , < 4e036c10e7f4df5d951c69cc3697bc8e209c6d02 (git)	guessed
Linux	Linux	Affected: 2.6.35 Unaffected: 0 , < 2.6.35 (semver) Unaffected: 5.15.210 , ≤ 5.15.* (semver) Unaffected: 6.1.176 , ≤ 6.1.* (semver) Unaffected: 6.6.143 , ≤ 6.6.* (semver) Unaffected: 6.12.93 , ≤ 6.12.* (semver) Unaffected: 6.18.35 , ≤ 6.18.* (semver) Unaffected: 7.0.12 , ≤ 7.0.* (semver) Unaffected: 7.1 , ≤ * (original_commit_for_fix)	guessed

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{
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        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: copy only received bytes on short ep0 read\n\nffs_ep0_read() allocates its control-OUT data buffer with\nkmalloc() (not kzalloc) at the Length value from the Setup\npacket, then copies that full len to userspace regardless of\nhow many bytes were actually received:\n\n    data = kmalloc(len, GFP_KERNEL);\n    ...\n    ret = __ffs_ep0_queue_wait(ffs, data, len);\n    if ((ret \u003e 0) \u0026\u0026 (copy_to_user(buf, data, len)))\n            ret = -EFAULT;\n\n__ffs_ep0_queue_wait() returns req-\u003eactual, which on a short\ncontrol OUT transfer is strictly less than len.  The\ncopy_to_user() call still copies len bytes, so on a short OUT\nthe last (len - ret) bytes of the kmalloc() buffer --\nuninitialised slab residue -- are delivered to the FunctionFS\ndaemon.\n\nShort ep0 OUT completions are specified USB control-transfer\nbehavior and are produced by in-tree UDCs:\n\n  * dwc2 continues on req-\u003eactual \u003c req-\u003elength for ep0 DATA OUT\n    (short-not-ok is the only ep0-OUT stall path).\n  * aspeed_udc ends ep0 OUT on rx_len \u003c ep-\u003eep.maxpacket.\n  * renesas_usbf logs \"ep0 short packet\" and completes the\n    request.\n  * dwc3 stalls on short IN but not on short OUT.\n\nA short ep0 OUT is therefore not evidence of a broken UDC; it is\na normal condition f_fs has to cope with.  The sibling gadgetfs\nimplementation in drivers/usb/gadget/legacy/inode.c already does\nthis correctly via min(len, dev-\u003ereq-\u003eactual) before\ncopy_to_user().  This patch brings f_fs.c to the same safe\npattern rather than trimming at a defensive layer.\n\nThe bug is reached from the FunctionFS device node, which in\nreal deployments is owned by the privileged gadget daemon\n(adbd, UMS, composite gadget services, etc.); it is not\nreachable from unprivileged userspace.  Linux host stacks\nnormally reject short-wLength control OUTs before they reach\nthe gadget, so reproducing this required a build that\nbypasses that host-side check.  With the bypass in place, a\n1-byte payload on a 64-byte Setup produces 63 bytes of\nnon-canary slab residue in the daemon\u0027s read buffer.\n\nFix by copying only ret (actually received) bytes to\nuserspace."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-19T14:55:05.479Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/90ccf5fb63243fae1b4b3200f3310500500ecf2e"
        },
        {
          "url": "https://git.kernel.org/stable/c/af32dbb2ca0b3d09271ab718d13857a457fa16f2"
        },
        {
          "url": "https://git.kernel.org/stable/c/e835bf9a055f71874065a40780ca5560b7df8b33"
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        {
          "url": "https://git.kernel.org/stable/c/88874a19b2b093bfaaa1c0090fa536c44da8c08b"
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        },
        {
          "url": "https://git.kernel.org/stable/c/23c1f7deb9dd8447ecde749850676302aa1e2bd3"
        },
        {
          "url": "https://git.kernel.org/stable/c/4e036c10e7f4df5d951c69cc3697bc8e209c6d02"
        }
      ],
      "title": "usb: gadget: f_fs: copy only received bytes on short ep0 read",
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    "datePublished": "2026-07-19T14:55:05.479Z",
    "dateReserved": "2026-07-19T07:54:57.019Z",
    "dateUpdated": "2026-07-19T14:55:05.479Z",
    "state": "PUBLISHED"
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: copy only received bytes on short ep0 read\n\nffs_ep0_read() allocates its control-OUT data buffer with\nkmalloc() (not kzalloc) at the Length value from the Setup\npacket, then copies that full len to userspace regardless of\nhow many bytes were actually received:\n\n    data = kmalloc(len, GFP_KERNEL);\n    ...\n    ret = __ffs_ep0_queue_wait(ffs, data, len);\n    if ((ret \u003e 0) \u0026\u0026 (copy_to_user(buf, data, len)))\n            ret = -EFAULT;\n\n__ffs_ep0_queue_wait() returns req-\u003eactual, which on a short\ncontrol OUT transfer is strictly less than len.  The\ncopy_to_user() call still copies len bytes, so on a short OUT\nthe last (len - ret) bytes of the kmalloc() buffer --\nuninitialised slab residue -- are delivered to the FunctionFS\ndaemon.\n\nShort ep0 OUT completions are specified USB control-transfer\nbehavior and are produced by in-tree UDCs:\n\n  * dwc2 continues on req-\u003eactual \u003c req-\u003elength for ep0 DATA OUT\n    (short-not-ok is the only ep0-OUT stall path).\n  * aspeed_udc ends ep0 OUT on rx_len \u003c ep-\u003eep.maxpacket.\n  * renesas_usbf logs \"ep0 short packet\" and completes the\n    request.\n  * dwc3 stalls on short IN but not on short OUT.\n\nA short ep0 OUT is therefore not evidence of a broken UDC; it is\na normal condition f_fs has to cope with.  The sibling gadgetfs\nimplementation in drivers/usb/gadget/legacy/inode.c already does\nthis correctly via min(len, dev-\u003ereq-\u003eactual) before\ncopy_to_user().  This patch brings f_fs.c to the same safe\npattern rather than trimming at a defensive layer.\n\nThe bug is reached from the FunctionFS device node, which in\nreal deployments is owned by the privileged gadget daemon\n(adbd, UMS, composite gadget services, etc.); it is not\nreachable from unprivileged userspace.  Linux host stacks\nnormally reject short-wLength control OUTs before they reach\nthe gadget, so reproducing this required a build that\nbypasses that host-side check.  With the bypass in place, a\n1-byte payload on a 64-byte Setup produces 63 bytes of\nnon-canary slab residue in the daemon\u0027s read buffer.\n\nFix by copying only ret (actually received) bytes to\nuserspace."
          }
        ],
        "id": "CVE-2026-63895",
        "lastModified": "2026-07-27T17:44:23.777",
        "metrics": {},
        "published": "2026-07-19T16:17:06.990",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/23c1f7deb9dd8447ecde749850676302aa1e2bd3"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/607730a414773a7cbe3037a64a6c64e72689ff5e"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/88874a19b2b093bfaaa1c0090fa536c44da8c08b"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/90ccf5fb63243fae1b4b3200f3310500500ecf2e"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/af32dbb2ca0b3d09271ab718d13857a457fa16f2"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/e835bf9a055f71874065a40780ca5560b7df8b33"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Awaiting Analysis"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-07-21T21:13:40+00:00",
      "cve": "CVE-2026-63895",
      "id": "CVE-2026-63895",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: usb: gadget: f_fs: copy only received bytes on short ep0 read",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63895.json",
      "version": "3"
    }
  }
}

FKIE_CVE-2026-63895

Vulnerability from fkie_nvd - Published: 2026-07-19 16:17 - Updated: 2026-07-27 17:44

Severity

Summary

References

	URL	Tags
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/23c1f7deb9dd8447ecde749850676302aa1e2bd3
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/4e036c10e7f4df5d951c69cc3697bc8e209c6d02
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/607730a414773a7cbe3037a64a6c64e72689ff5e
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/88874a19b2b093bfaaa1c0090fa536c44da8c08b
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/90ccf5fb63243fae1b4b3200f3310500500ecf2e
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/af32dbb2ca0b3d09271ab718d13857a457fa16f2
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/e835bf9a055f71874065a40780ca5560b7df8b33

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/gadget/function/f_fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "90ccf5fb63243fae1b4b3200f3310500500ecf2e",
              "status": "affected",
              "version": "ddf8abd2599491cbad959c700b90ba72a5dce8d0",
              "versionType": "git"
            },
            {
              "lessThan": "af32dbb2ca0b3d09271ab718d13857a457fa16f2",
              "status": "affected",
              "version": "ddf8abd2599491cbad959c700b90ba72a5dce8d0",
              "versionType": "git"
            },
            {
              "lessThan": "e835bf9a055f71874065a40780ca5560b7df8b33",
              "status": "affected",
              "version": "ddf8abd2599491cbad959c700b90ba72a5dce8d0",
              "versionType": "git"
            },
            {
              "lessThan": "88874a19b2b093bfaaa1c0090fa536c44da8c08b",
              "status": "affected",
              "version": "ddf8abd2599491cbad959c700b90ba72a5dce8d0",
              "versionType": "git"
            },
            {
              "lessThan": "607730a414773a7cbe3037a64a6c64e72689ff5e",
              "status": "affected",
              "version": "ddf8abd2599491cbad959c700b90ba72a5dce8d0",
              "versionType": "git"
            },
            {
              "lessThan": "23c1f7deb9dd8447ecde749850676302aa1e2bd3",
              "status": "affected",
              "version": "ddf8abd2599491cbad959c700b90ba72a5dce8d0",
              "versionType": "git"
            },
            {
              "lessThan": "4e036c10e7f4df5d951c69cc3697bc8e209c6d02",
              "status": "affected",
              "version": "ddf8abd2599491cbad959c700b90ba72a5dce8d0",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "drivers/usb/gadget/function/f_fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.35"
            },
            {
              "lessThan": "2.6.35",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.210",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.176",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.143",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.93",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.35",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: copy only received bytes on short ep0 read\n\nffs_ep0_read() allocates its control-OUT data buffer with\nkmalloc() (not kzalloc) at the Length value from the Setup\npacket, then copies that full len to userspace regardless of\nhow many bytes were actually received:\n\n    data = kmalloc(len, GFP_KERNEL);\n    ...\n    ret = __ffs_ep0_queue_wait(ffs, data, len);\n    if ((ret \u003e 0) \u0026\u0026 (copy_to_user(buf, data, len)))\n            ret = -EFAULT;\n\n__ffs_ep0_queue_wait() returns req-\u003eactual, which on a short\ncontrol OUT transfer is strictly less than len.  The\ncopy_to_user() call still copies len bytes, so on a short OUT\nthe last (len - ret) bytes of the kmalloc() buffer --\nuninitialised slab residue -- are delivered to the FunctionFS\ndaemon.\n\nShort ep0 OUT completions are specified USB control-transfer\nbehavior and are produced by in-tree UDCs:\n\n  * dwc2 continues on req-\u003eactual \u003c req-\u003elength for ep0 DATA OUT\n    (short-not-ok is the only ep0-OUT stall path).\n  * aspeed_udc ends ep0 OUT on rx_len \u003c ep-\u003eep.maxpacket.\n  * renesas_usbf logs \"ep0 short packet\" and completes the\n    request.\n  * dwc3 stalls on short IN but not on short OUT.\n\nA short ep0 OUT is therefore not evidence of a broken UDC; it is\na normal condition f_fs has to cope with.  The sibling gadgetfs\nimplementation in drivers/usb/gadget/legacy/inode.c already does\nthis correctly via min(len, dev-\u003ereq-\u003eactual) before\ncopy_to_user().  This patch brings f_fs.c to the same safe\npattern rather than trimming at a defensive layer.\n\nThe bug is reached from the FunctionFS device node, which in\nreal deployments is owned by the privileged gadget daemon\n(adbd, UMS, composite gadget services, etc.); it is not\nreachable from unprivileged userspace.  Linux host stacks\nnormally reject short-wLength control OUTs before they reach\nthe gadget, so reproducing this required a build that\nbypasses that host-side check.  With the bypass in place, a\n1-byte payload on a 64-byte Setup produces 63 bytes of\nnon-canary slab residue in the daemon\u0027s read buffer.\n\nFix by copying only ret (actually received) bytes to\nuserspace."
    }
  ],
  "id": "CVE-2026-63895",
  "lastModified": "2026-07-27T17:44:23.777",
  "metrics": {},
  "published": "2026-07-19T16:17:06.990",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/23c1f7deb9dd8447ecde749850676302aa1e2bd3"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4e036c10e7f4df5d951c69cc3697bc8e209c6d02"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/607730a414773a7cbe3037a64a6c64e72689ff5e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/88874a19b2b093bfaaa1c0090fa536c44da8c08b"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/90ccf5fb63243fae1b4b3200f3310500500ecf2e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/af32dbb2ca0b3d09271ab718d13857a457fa16f2"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e835bf9a055f71874065a40780ca5560b7df8b33"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}

GHSA-HQP4-GW43-6PCC

Vulnerability from github – Published: 2026-07-19 18:31 – Updated: 2026-07-19 18:31

Details

In the Linux kernel, the following vulnerability has been resolved:

usb: gadget: f_fs: copy only received bytes on short ep0 read

ffs_ep0_read() allocates its control-OUT data buffer with kmalloc() (not kzalloc) at the Length value from the Setup packet, then copies that full len to userspace regardless of how many bytes were actually received:

data = kmalloc(len, GFP_KERNEL);
...
ret = __ffs_ep0_queue_wait(ffs, data, len);
if ((ret > 0) && (copy_to_user(buf, data, len)))
        ret = -EFAULT;

__ffs_ep0_queue_wait() returns req->actual, which on a short control OUT transfer is strictly less than len. The copy_to_user() call still copies len bytes, so on a short OUT the last (len - ret) bytes of the kmalloc() buffer -- uninitialised slab residue -- are delivered to the FunctionFS daemon.

Short ep0 OUT completions are specified USB control-transfer behavior and are produced by in-tree UDCs:

dwc2 continues on req->actual < req->length for ep0 DATA OUT (short-not-ok is the only ep0-OUT stall path).
aspeed_udc ends ep0 OUT on rx_len < ep->ep.maxpacket.
renesas_usbf logs "ep0 short packet" and completes the request.
dwc3 stalls on short IN but not on short OUT.

A short ep0 OUT is therefore not evidence of a broken UDC; it is a normal condition f_fs has to cope with. The sibling gadgetfs implementation in drivers/usb/gadget/legacy/inode.c already does this correctly via min(len, dev->req->actual) before copy_to_user(). This patch brings f_fs.c to the same safe pattern rather than trimming at a defensive layer.

The bug is reached from the FunctionFS device node, which in real deployments is owned by the privileged gadget daemon (adbd, UMS, composite gadget services, etc.); it is not reachable from unprivileged userspace. Linux host stacks normally reject short-wLength control OUTs before they reach the gadget, so reproducing this required a build that bypasses that host-side check. With the bypass in place, a 1-byte payload on a 64-byte Setup produces 63 bytes of non-canary slab residue in the daemon's read buffer.

Fix by copying only ret (actually received) bytes to userspace.

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-63895"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-19T16:17:06Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nusb: gadget: f_fs: copy only received bytes on short ep0 read\n\nffs_ep0_read() allocates its control-OUT data buffer with\nkmalloc() (not kzalloc) at the Length value from the Setup\npacket, then copies that full len to userspace regardless of\nhow many bytes were actually received:\n\n    data = kmalloc(len, GFP_KERNEL);\n    ...\n    ret = __ffs_ep0_queue_wait(ffs, data, len);\n    if ((ret \u003e 0) \u0026\u0026 (copy_to_user(buf, data, len)))\n            ret = -EFAULT;\n\n__ffs_ep0_queue_wait() returns req-\u003eactual, which on a short\ncontrol OUT transfer is strictly less than len.  The\ncopy_to_user() call still copies len bytes, so on a short OUT\nthe last (len - ret) bytes of the kmalloc() buffer --\nuninitialised slab residue -- are delivered to the FunctionFS\ndaemon.\n\nShort ep0 OUT completions are specified USB control-transfer\nbehavior and are produced by in-tree UDCs:\n\n  * dwc2 continues on req-\u003eactual \u003c req-\u003elength for ep0 DATA OUT\n    (short-not-ok is the only ep0-OUT stall path).\n  * aspeed_udc ends ep0 OUT on rx_len \u003c ep-\u003eep.maxpacket.\n  * renesas_usbf logs \"ep0 short packet\" and completes the\n    request.\n  * dwc3 stalls on short IN but not on short OUT.\n\nA short ep0 OUT is therefore not evidence of a broken UDC; it is\na normal condition f_fs has to cope with.  The sibling gadgetfs\nimplementation in drivers/usb/gadget/legacy/inode.c already does\nthis correctly via min(len, dev-\u003ereq-\u003eactual) before\ncopy_to_user().  This patch brings f_fs.c to the same safe\npattern rather than trimming at a defensive layer.\n\nThe bug is reached from the FunctionFS device node, which in\nreal deployments is owned by the privileged gadget daemon\n(adbd, UMS, composite gadget services, etc.); it is not\nreachable from unprivileged userspace.  Linux host stacks\nnormally reject short-wLength control OUTs before they reach\nthe gadget, so reproducing this required a build that\nbypasses that host-side check.  With the bypass in place, a\n1-byte payload on a 64-byte Setup produces 63 bytes of\nnon-canary slab residue in the daemon\u0027s read buffer.\n\nFix by copying only ret (actually received) bytes to\nuserspace.",
  "id": "GHSA-hqp4-gw43-6pcc",
  "modified": "2026-07-19T18:31:44Z",
  "published": "2026-07-19T18:31:44Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63895"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/23c1f7deb9dd8447ecde749850676302aa1e2bd3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4e036c10e7f4df5d951c69cc3697bc8e209c6d02"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/607730a414773a7cbe3037a64a6c64e72689ff5e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/88874a19b2b093bfaaa1c0090fa536c44da8c08b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/90ccf5fb63243fae1b4b3200f3310500500ecf2e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/af32dbb2ca0b3d09271ab718d13857a457fa16f2"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e835bf9a055f71874065a40780ca5560b7df8b33"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

OPENSUSE-SU-2026:21555-1

Vulnerability from csaf_opensuse - Published: 2026-08-12 01:09 - Updated: 2026-10-20 09:52

Summary

Security update for the Linux Kernel

Severity

Important

Scope

894 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 136 products

Open the full advisory

SUSE-SU-2026:23066-1

Vulnerability from csaf_suse - Published: 2026-08-11 20:56 - Updated: 2026-10-20 09:48

Summary

Security update for the Linux Kernel

Severity

Important

Scope

894 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 8 products

Open the full advisory

SUSE-SU-2026:23068-1

Vulnerability from csaf_suse - Published: 2026-08-11 21:26 - Updated: 2026-10-20 09:48

Summary

Security update for the Linux Kernel

Severity

Important

Scope

894 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 28 products

Open the full advisory

SUSE-SU-2026:23193-1

Vulnerability from csaf_suse - Published: 2026-08-18 18:56 - Updated: 2026-10-21 19:03

Summary

Security update for the Linux Kernel

Severity

Important

Scope

648 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 7 products

Open the full advisory

SUSE-SU-2026:23194-1

Vulnerability from csaf_suse - Published: 2026-08-18 19:48 - Updated: 2026-10-21 19:03

Summary

Security update for the Linux Kernel

Severity

Important

Scope

647 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 14 products

Open the full advisory

SUSE-SU-2026:23221-1

Vulnerability from csaf_suse - Published: 2026-08-11 21:26 - Updated: 2026-10-20 09:48

Summary

Security update for the Linux Kernel

Severity

Important

Scope

894 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 114 products

Open the full advisory

SUSE-SU-2026:23231-1

Vulnerability from csaf_suse - Published: 2026-08-11 21:26 - Updated: 2026-10-20 09:48

Summary

Security update for the Linux Kernel

Severity

Important

Scope

894 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 114 products

Open the full advisory

SUSE-SU-2026:23237-1

Vulnerability from csaf_suse - Published: 2026-08-11 21:34 - Updated: 2026-10-20 09:48

Summary

Security update for the Linux Kernel

Severity

Important

Scope

894 vulnerabilities in this advisory, including CVE-2026-63895.

CVE-2026-63895

2.4 (Low)


                
                  CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Recommended: 9 products

Open the full advisory

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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CVE-2026-63895 (GCVE-0-2026-63895)

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