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

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-07-19 14:55
VLAI
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
References
Impacted products
Vendor Product Version
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)
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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)
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{
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      "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."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-19T14:55:05.479Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/90ccf5fb63243fae1b4b3200f3310500500ecf2e"
        },
        {
          "url": "https://git.kernel.org/stable/c/af32dbb2ca0b3d09271ab718d13857a457fa16f2"
        },
        {
          "url": "https://git.kernel.org/stable/c/e835bf9a055f71874065a40780ca5560b7df8b33"
        },
        {
          "url": "https://git.kernel.org/stable/c/88874a19b2b093bfaaa1c0090fa536c44da8c08b"
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          "url": "https://git.kernel.org/stable/c/607730a414773a7cbe3037a64a6c64e72689ff5e"
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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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        "engine": "bippy-1.2.0"
      }
    }
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63895",
    "datePublished": "2026-07-19T14:55:05.479Z",
    "dateReserved": "2026-07-19T07:54:57.019Z",
    "dateUpdated": "2026-07-19T14:55:05.479Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-63895",
      "date": "2026-07-21",
      "epss": "0.00244",
      "percentile": "0.15596"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-63895\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-07-19T16:17:06.990\",\"lastModified\":\"2026-07-19T16:17:06.990\",\"vulnStatus\":\"Received\",\"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.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"drivers/usb/gadget/function/f_fs.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"ddf8abd2599491cbad959c700b90ba72a5dce8d0\",\"lessThan\":\"90ccf5fb63243fae1b4b3200f3310500500ecf2e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"ddf8abd2599491cbad959c700b90ba72a5dce8d0\",\"lessThan\":\"af32dbb2ca0b3d09271ab718d13857a457fa16f2\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"ddf8abd2599491cbad959c700b90ba72a5dce8d0\",\"lessThan\":\"e835bf9a055f71874065a40780ca5560b7df8b33\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"ddf8abd2599491cbad959c700b90ba72a5dce8d0\",\"lessThan\":\"88874a19b2b093bfaaa1c0090fa536c44da8c08b\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"ddf8abd2599491cbad959c700b90ba72a5dce8d0\",\"lessThan\":\"607730a414773a7cbe3037a64a6c64e72689ff5e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"ddf8abd2599491cbad959c700b90ba72a5dce8d0\",\"lessThan\":\"23c1f7deb9dd8447ecde749850676302aa1e2bd3\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"ddf8abd2599491cbad959c700b90ba72a5dce8d0\",\"lessThan\":\"4e036c10e7f4df5d951c69cc3697bc8e209c6d02\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"drivers/usb/gadget/function/f_fs.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2.6.35\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"2.6.35\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.210\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.176\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.143\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.93\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.35\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.0.12\",\"lessThanOrEqual\":\"7.0.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{},\"references\":[{\"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\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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  • 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.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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