GHSA-3QPP-VV65-CQ9G
Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 15:31In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix heap overflow in DACL owner/group rewrite
When id_mode_to_cifs_acl rewrites an existing DACL, it allocates a buffer sized according to the on-disk DACL length reported by dacl_ptr->size. However, replace_sids_and_copy_aces may rewrite each ACE with a new owner/group SID obtained from the cifs.idmap upcall. Those SIDs can have up to SID_MAX_SUB_AUTHORITIES (15) sub-authorities, making each ACE up to 76 bytes (sizeof(struct smb_ace)).
If the original DACL contains short SIDs (e.g., 1 sub-authority) while the replacement SIDs are long, the rewritten ACEs overflow the allocation.
Fix this by always budgeting for worst-case SID expansion: allocate sizeof(struct smb_acl) plus num_aces * sizeof(struct smb_ace), which covers the smb_acl header and room for every ACE at maximum SID size. This replaces the previous split logic that used dacl_ptr->size for cifsacl mounts but num_aces * sizeof(struct smb_ace) for mode_from_sid mounts: both paths can trigger the same rewrite and need the same headroom.
KASAN reports this as: BUG: KASAN: slab-out-of-bounds in build_sec_desc+0x1e8a/0x2680 [cifs] Write of size 4 at addr ffff8881a5e25374 by task chown/5298 ... The buggy address is located 0 bytes to the right of allocated 884-byte region [ffff8881a5e25000, ffff8881a5e25374)
{
"affected": [],
"aliases": [
"CVE-2026-97555"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-25T11:17:05Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix heap overflow in DACL owner/group rewrite\n\nWhen id_mode_to_cifs_acl rewrites an existing DACL, it allocates a\nbuffer sized according to the on-disk DACL length reported by\ndacl_ptr-\u003esize. However, replace_sids_and_copy_aces may rewrite each\nACE with a new owner/group SID obtained from the cifs.idmap upcall.\nThose SIDs can have up to SID_MAX_SUB_AUTHORITIES (15) sub-authorities,\nmaking each ACE up to 76 bytes (sizeof(struct smb_ace)).\n\nIf the original DACL contains short SIDs (e.g., 1 sub-authority) while\nthe replacement SIDs are long, the rewritten ACEs overflow the\nallocation.\n\nFix this by always budgeting for worst-case SID expansion: allocate\nsizeof(struct smb_acl) plus num_aces * sizeof(struct smb_ace), which\ncovers the smb_acl header and room for every ACE at maximum SID size.\nThis replaces the previous split logic that used dacl_ptr-\u003esize for\ncifsacl mounts but num_aces * sizeof(struct smb_ace) for mode_from_sid\nmounts: both paths can trigger the same rewrite and need the same\nheadroom.\n\nKASAN reports this as:\n BUG: KASAN: slab-out-of-bounds in build_sec_desc+0x1e8a/0x2680 [cifs]\n Write of size 4 at addr ffff8881a5e25374 by task chown/5298\n ...\n The buggy address is located 0 bytes to the right of\n allocated 884-byte region [ffff8881a5e25000, ffff8881a5e25374)",
"id": "GHSA-3qpp-vv65-cq9g",
"modified": "2026-09-25T15:31:42Z",
"published": "2026-09-25T12:31:24Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-97555"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/0ee150794c75bcd0be0e24ff3394f433cbae18cc"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2a9aee9ef5622d58d8aafaa3263b3ffe70e2d9dd"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7fa84c9ca690643f429ae2709584a47e74b572c9"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fb736ab4fb8c4fdb8b2f9ccd3a62e03d11549ca1"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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