cifs: remove check of list iterator against head past the loop body

When list_for_each_entry() completes the iteration over the whole list
without breaking the loop, the iterator value will be a bogus pointer
computed based on the head element.

While it is safe to use the pointer to determine if it was computed
based on the head element, either with list_entry_is_head() or
&pos->member == head, using the iterator variable after the loop should
be avoided.

In preparation to limit the scope of a list iterator to the list
traversal loop, use a dedicated pointer to point to the found element [1].

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c
index c653beb735b89f9aa0d32fdf13a0e8e771622e65..3fe47a88f47d0d0a373d4cb8ce0c13bb57b6b9d2 100644 (file)
--- a/fs/cifs/smb2misc.c
+++ b/fs/cifs/smb2misc.c
@@ -150,16 +150,18 @@ smb2_check_message(char *buf, unsigned int len, struct TCP_Server_Info *srvr)
                struct smb2_transform_hdr *thdr =
                        (struct smb2_transform_hdr *)buf;
                struct cifs_ses *ses = NULL;
+               struct cifs_ses *iter;
 
                /* decrypt frame now that it is completely read in */
                spin_lock(&cifs_tcp_ses_lock);
-               list_for_each_entry(ses, &srvr->smb_ses_list, smb_ses_list) {
-                       if (ses->Suid == le64_to_cpu(thdr->SessionId))
+               list_for_each_entry(iter, &srvr->smb_ses_list, smb_ses_list) {
+                       if (iter->Suid == le64_to_cpu(thdr->SessionId)) {
+                               ses = iter;
                                break;
+                       }
                }
                spin_unlock(&cifs_tcp_ses_lock);
-               if (list_entry_is_head(ses, &srvr->smb_ses_list,
-                                      smb_ses_list)) {
+               if (!ses) {
                        cifs_dbg(VFS, "no decryption - session id not found\n");
                        return 1;
                }