smb: client: fix potential UAF in cifs_stats_proc_show()

commit 0865ffe upstream.

Skip sessions that are being teared down (status == SES_EXITING) to
avoid UAF.

Cc: [email protected]
Signed-off-by: Paulo Alcantara (Red Hat) <[email protected]>
Signed-off-by: Steve French <[email protected]>
[ cifs_debug.c was moved from fs/cifs to fs/smb/client since
  38c8a9a ("smb: move client and server files to common directory fs/smb").
  The cifs_ses_exiting() was introduced to cifs_debug.c since
  ca545b7 ("smb: client: fix potential UAF in cifs_debug_files_proc_show()")
  which has been sent to upstream already. ]
Signed-off-by: Jianqi Ren <[email protected]>
Signed-off-by: He Zhe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
(cherry picked from commit bb6570085826291dc392005f9fec16ea5da3c8ad)
Signed-off-by: Vijayendra Suman <[email protected]>

Author: Paulo Alcantara

fs/cifs/cifs_debug.c

@@ -613,6 +613,8 @@ static int cifs_stats_proc_show(struct seq_file *m, void *v)
 		list_for_each(tmp2, &server->smb_ses_list) {
 			ses = list_entry(tmp2, struct cifs_ses,
 					 smb_ses_list);
+			if (cifs_ses_exiting(ses))
+				continue;
 			list_for_each(tmp3, &ses->tcon_list) {
 				tcon = list_entry(tmp3,
 						  struct cifs_tcon,