5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Bjoern Doebel [ Upstream commit 0ee150794c75bcd0be0e24ff3394f433cbae18cc ] 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) Cc: stable@vger.kernel.org Fixes: bc3e9dd9d104 ("cifs: Change SIDs in ACEs while transferring file ownership.") Assisted-by: Kiro:claude-opus-4.6 Signed-off-by: Bjoern Doebel Reviewed-by: Namjae Jeon Fixes: 5c3564852c58 ("cifs: Minimize the number of cifs_acl memory allocations") Signed-off-by: Paulo Alcantara [ changed smb_acl/smb_ace to cifs_acl/cifs_ace and le16_to_cpu() to le32_to_cpu() for the branch’s 32-bit num_aces field. ] Signed-off-by: Sasha Levin --- fs/cifs/cifsacl.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c index 19d2d68706ad0..3baafbc12f1a1 100644 --- a/fs/cifs/cifsacl.c +++ b/fs/cifs/cifsacl.c @@ -1747,11 +1747,13 @@ id_mode_to_cifs_acl(struct inode *inode, const char *path, __u64 *pnmode, cifs_put_tlink(tlink); return rc; } - if (mode_from_sid) - nsecdesclen += - le32_to_cpu(dacl_ptr->num_aces) * sizeof(struct cifs_ace); - else /* cifsacl */ - nsecdesclen += le16_to_cpu(dacl_ptr->size); + /* + * Worst case: every ACE is rewritten with a new SID of + * SID_MAX_SUB_AUTHORITIES sub-auths -> sizeof(cifs_ace) each, + * plus the cifs_acl header replace_sids_and_copy_aces() emits. + */ + nsecdesclen += sizeof(struct cifs_acl) + + le32_to_cpu(dacl_ptr->num_aces) * sizeof(struct cifs_ace); } } -- 2.53.0