From: Ali Ganiyev Date: Mon, 25 May 2026 01:23:47 +0000 (+0900) Subject: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops X-Git-Tag: v7.1-rc6~12^2~2 X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=0e60dafe97eca61721f3db456f97d97a80c6c8ae;p=thirdparty%2Flinux.git ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl(). Fixes: d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") Cc: stable@vger.kernel.org Signed-off-by: Ali Ganiyev Acked-by: Namjae Jeon Signed-off-by: Steve French --- diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index c2d9be52a311f..664b1b4a3233d 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -1446,8 +1446,8 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); aces_size = acl_size - sizeof(struct smb_acl); for (i = 0; i < le16_to_cpu(pdacl->num_aces); i++) { - if (offsetof(struct smb_ace, sid) + - aces_size < CIFS_SID_BASE_SIZE) + if (aces_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; ace_size = le16_to_cpu(ace->size); if (ace_size > aces_size || @@ -1467,8 +1467,8 @@ int smb_check_perm_dacl(struct ksmbd_conn *conn, const struct path *path, ace = (struct smb_ace *)((char *)pdacl + sizeof(struct smb_acl)); aces_size = acl_size - sizeof(struct smb_acl); for (i = 0; i < le16_to_cpu(pdacl->num_aces); i++) { - if (offsetof(struct smb_ace, sid) + - aces_size < CIFS_SID_BASE_SIZE) + if (aces_size < offsetof(struct smb_ace, sid) + + CIFS_SID_BASE_SIZE) break; ace_size = le16_to_cpu(ace->size); if (ace_size > aces_size ||