From: Michael Bommarito Date: Mon, 20 Apr 2026 13:50:58 +0000 (-0400) Subject: smb: client: require a full NFS mode SID before reading mode bits X-Git-Tag: v7.1-rc1~35^2~12 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2757ad3e4b6f9e0fed4c7739594e702abc5cab21;p=thirdparty%2Fkernel%2Flinux.git smb: client: require a full NFS mode SID before reading mode bits parse_dacl() treats an ACE SID matching sid_unix_NFS_mode as an NFS mode SID and reads sid.sub_auth[2] to recover the mode bits. That assumes the ACE carries three subauthorities, but compare_sids() only compares min(a, b) subauthorities. A malicious server can return an ACE with num_subauth = 2 and sub_auth[] = {88, 3}, which still matches sid_unix_NFS_mode and then drives the sub_auth[2] read four bytes past the end of the ACE. Require num_subauth >= 3 before treating the ACE as an NFS mode SID. This keeps the fix local to the special-SID mode path without changing compare_sids() semantics for the rest of cifsacl. Fixes: e2f8fbfb8d09 ("cifs: get mode bits from special sid on stat") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Michael Bommarito Signed-off-by: Steve French --- diff --git a/fs/smb/client/cifsacl.c b/fs/smb/client/cifsacl.c index cb4060ba5e31..4ec204d2c774 100644 --- a/fs/smb/client/cifsacl.c +++ b/fs/smb/client/cifsacl.c @@ -879,6 +879,7 @@ static void parse_dacl(struct smb_acl *pdacl, char *end_of_acl, dump_ace(ppace[i], end_of_dacl); #endif if (mode_from_special_sid && + ppace[i]->sid.num_subauth >= 3 && (compare_sids(&(ppace[i]->sid), &sid_unix_NFS_mode) == 0)) { /*