CVE-2026-97555smb: client: fix heap overflow in DACL owner/group rewrite

Official description

In 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 packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/4e78b5ff13214353750b87283ff79f62510f5844
• https://git.kernel.org/stable/c/63c2fbde15ffc9a0c21adf670c38d028e20fa65c
• https://git.kernel.org/stable/c/d5cea6766ae1868a51c7d17d77d065b4f55c587f
• https://git.kernel.org/stable/c/fb736ab4fb8c4fdb8b2f9ccd3a62e03d11549ca1
• https://git.kernel.org/stable/c/7fa84c9ca690643f429ae2709584a47e74b572c9
• https://git.kernel.org/stable/c/2a9aee9ef5622d58d8aafaa3263b3ffe70e2d9dd
• https://git.kernel.org/stable/c/0ee150794c75bcd0be0e24ff3394f433cbae18cc