From: Greg Kroah-Hartman Date: Mon, 6 Apr 2026 13:46:47 +0000 (+0200) Subject: ksmbd: require 3 sub-authorities before reading sub_auth[2] X-Git-Tag: v7.1-rc1~136^2~7 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=53370cf9090777774e07fd9a8ebce67c6cc333ab;p=thirdparty%2Fkernel%2Flinux.git ksmbd: require 3 sub-authorities before reading sub_auth[2] parse_dacl() compares each ACE SID against sid_unix_NFS_mode and on match reads sid.sub_auth[2] as the file mode. If sid_unix_NFS_mode is the prefix S-1-5-88-3 with num_subauth = 2 then compare_sids() compares only min(num_subauth, 2) sub-authorities so a client SID with num_subauth = 2 and sub_auth = {88, 3} will match. If num_subauth = 2 and the ACE is placed at the very end of the security descriptor, sub_auth[2] will be 4 bytes past end_of_acl. The out-of-band bytes will then be masked to the low 9 bits and applied as the file's POSIX mode, probably not something that is good to have happen. Fix this up by forcing the SID to actually carry a third sub-authority before reading it at all. Cc: Namjae Jeon Cc: Steve French Cc: Sergey Senozhatsky Cc: Tom Talpey Cc: linux-cifs@vger.kernel.org Cc: Assisted-by: gregkh_clanker_t1000 Signed-off-by: Greg Kroah-Hartman Acked-by: Namjae Jeon Signed-off-by: Steve French --- diff --git a/fs/smb/server/smbacl.c b/fs/smb/server/smbacl.c index c30d01877c418..061a305bf9c8b 100644 --- a/fs/smb/server/smbacl.c +++ b/fs/smb/server/smbacl.c @@ -451,7 +451,8 @@ static void parse_dacl(struct mnt_idmap *idmap, ppace[i]->access_req = smb_map_generic_desired_access(ppace[i]->access_req); - if (!(compare_sids(&ppace[i]->sid, &sid_unix_NFS_mode))) { + if (ppace[i]->sid.num_subauth >= 3 && + !(compare_sids(&ppace[i]->sid, &sid_unix_NFS_mode))) { fattr->cf_mode = le32_to_cpu(ppace[i]->sid.sub_auth[2]); break;