GHSA-WW53-M8WH-V825

Vulnerability from github – Published: 2026-07-19 18:31 – Updated: 2026-07-20 15:31
VLAI
Details

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

scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()

Two latent bugs in the Text-phase handler, both present since the original LIO integration in commit e48354ce078c ("iscsi-target: Add iSCSI fabric support for target v4.1"):

1) DataDigest CRC buffer overread (4 bytes past text_in).

text_in is kzalloc()'d at ALIGN(payload_length, 4). rx_size is then incremented by ISCSI_CRC_LEN to make room for the received DataDigest in the iovec, but the same (now-bumped) rx_size is passed as the buffer length to iscsit_crc_buf():

   if (conn->conn_ops->DataDigest) {
           ...
           rx_size += ISCSI_CRC_LEN;
   }
   ...
   if (conn->conn_ops->DataDigest) {
           data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);

iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so when DataDigest is negotiated it reads 4 bytes past the end of the text_in allocation. KASAN reproduces this directly on the unpatched mainline tree as slab-out-of-bounds in crc32c() called from the Text PDU path. The OOB bytes feed crc32c() and are then compared against the initiator-supplied checksum, so the value does not flow back to the attacker, but the kernel does read past the buffer on every Text PDU with DataDigest=CRC32C.

Fix by passing the actual padded payload length (ALIGN(payload_length, 4)) that was used for the kzalloc().

2) Stale cmd->text_in_ptr re-free (double-free) on ERL>0 bad DataDigest drop.

On DataDigest mismatch with ErrorRecoveryLevel > 0 the handler silently drops the PDU and lets the initiator plug the CmdSN gap:

           kfree(text_in);
           return 0;

cmd->text_in_ptr still points at the freed buffer. The next Text Request on the same ITT re-enters iscsit_setup_text_cmd(), which unconditionally does

   kfree(cmd->text_in_ptr);
   cmd->text_in_ptr = NULL;

freeing the same pointer a second time. Session teardown via iscsit_release_cmd() has the same shape and hits the same double-free if the connection is dropped before a second Text Request arrives.

On an unmodified mainline tree the bug-1 CRC overread fires first on the initial valid Text Request and perturbs the subsequent state, so #4 was isolated by building a kernel with only the bug-1 hunk of this patch applied plus temporary printk() observability around the three relevant kfree() sites. The observability prints are not part of this patch. On that build, a three-PDU Text Request sequence after login produces two back-to-back splats:

   BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??
   BUG: KASAN: double-free in iscsit_release_cmd+0x??

showing the same pointer freed in the ERL>0 drop path and again in iscsit_setup_text_cmd() (next Text Request on the same ITT) and once more in iscsit_release_cmd() (session teardown). On distro kernels with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free becomes a remote kernel BUG(); on non-hardened kernels it corrupts the slab freelist.

Fix by clearing cmd->text_in_ptr after the kfree() in the ERL>0 drop path. With both hunks applied #4 is directly observable on the stock tree without observability printks; fixing bug-1 alone would mask #4 less, not more, so the hunks are submitted together.

Both fixes are one-liners. The Text PDU state machine is unchanged and the wire protocol is unaffected.

Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Show details on source website
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{
  "affected": [],
  "aliases": [
    "CVE-2026-63888"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-19T16:17:05Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nscsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()\n\nTwo latent bugs in the Text-phase handler, both present since the\noriginal LIO integration in commit e48354ce078c (\"iscsi-target: Add\niSCSI fabric support for target v4.1\"):\n\n1) DataDigest CRC buffer overread (4 bytes past text_in).\n\n   text_in is kzalloc()\u0027d at ALIGN(payload_length, 4).  rx_size is then\n   incremented by ISCSI_CRC_LEN to make room for the received DataDigest\n   in the iovec, but the same (now-bumped) rx_size is passed as the\n   buffer length to iscsit_crc_buf():\n\n       if (conn-\u003econn_ops-\u003eDataDigest) {\n               ...\n               rx_size += ISCSI_CRC_LEN;\n       }\n       ...\n       if (conn-\u003econn_ops-\u003eDataDigest) {\n               data_crc = iscsit_crc_buf(text_in, rx_size, 0, NULL);\n\n   iscsit_crc_buf() walks rx_size bytes of text_in with crc32c(), so\n   when DataDigest is negotiated it reads 4 bytes past the end of the\n   text_in allocation.  KASAN reproduces this directly on the unpatched\n   mainline tree as slab-out-of-bounds in crc32c() called from the Text\n   PDU path.  The OOB bytes feed crc32c() and are then compared against\n   the initiator-supplied checksum, so the value does not flow back to\n   the attacker, but the kernel does read past the buffer on every Text\n   PDU with DataDigest=CRC32C.\n\n   Fix by passing the actual padded payload length\n   (ALIGN(payload_length, 4)) that was used for the kzalloc().\n\n2) Stale cmd-\u003etext_in_ptr re-free (double-free) on ERL\u003e0 bad DataDigest\n   drop.\n\n   On DataDigest mismatch with ErrorRecoveryLevel \u003e 0 the handler\n   silently drops the PDU and lets the initiator plug the CmdSN gap:\n\n               kfree(text_in);\n               return 0;\n\n   cmd-\u003etext_in_ptr still points at the freed buffer.  The next Text\n   Request on the same ITT re-enters iscsit_setup_text_cmd(), which\n   unconditionally does\n\n       kfree(cmd-\u003etext_in_ptr);\n       cmd-\u003etext_in_ptr = NULL;\n\n   freeing the same pointer a second time.  Session teardown via\n   iscsit_release_cmd() has the same shape and hits the same double-free\n   if the connection is dropped before a second Text Request arrives.\n\n   On an unmodified mainline tree the bug-1 CRC overread fires first on\n   the initial valid Text Request and perturbs the subsequent state, so\n   #4 was isolated by building a kernel with only the bug-1 hunk of this\n   patch applied plus temporary printk() observability around the three\n   relevant kfree() sites.  The observability prints are not part of\n   this patch.  On that build, a three-PDU Text Request sequence after\n   login produces two back-to-back splats:\n\n       BUG: KASAN: double-free in iscsit_setup_text_cmd+0x??\n       BUG: KASAN: double-free in iscsit_release_cmd+0x??\n\n   showing the same pointer freed in the ERL\u003e0 drop path and again in\n   iscsit_setup_text_cmd() (next Text Request on the same ITT) and once\n   more in iscsit_release_cmd() (session teardown).  On distro kernels\n   with CONFIG_SLAB_FREELIST_HARDENED=y (default) the double-free\n   becomes a remote kernel BUG(); on non-hardened kernels it corrupts\n   the slab freelist.\n\n   Fix by clearing cmd-\u003etext_in_ptr after the kfree() in the ERL\u003e0 drop\n   path.  With both hunks applied #4 is directly observable on the stock\n   tree without observability printks; fixing bug-1 alone would mask #4\n   less, not more, so the hunks are submitted together.\n\nBoth fixes are one-liners.  The Text PDU state machine is unchanged and\nthe wire protocol is unaffected.",
  "id": "GHSA-ww53-m8wh-v825",
  "modified": "2026-07-20T15:31:50Z",
  "published": "2026-07-19T18:31:44Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63888"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5118ea225fe63b44207ba88047e4866e1ea43812"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/6e22a1cdcc8277af4acc43710577157b77a02c5d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/778c2ab142c625a8a8afa570e0f9b7873f445d99"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/89c81d1228c00fa6dd91de6c1c5aa1ef8a7875e3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/badf178b76b0690851df00f4ca9cf2eb8eb0f963"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d3e9b79aa794f7a23e82de4d710e7d2df610e349"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ec9f19d52074a191ed1756ed4a7d39fff1a2085c"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f7948af0dd03de84079dcd4dc215a69fd6fbb95d"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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