cifs: check for NULL last_entry before calling cifs_save_resume_key

Prior to commit eaf35b1, cifs_save_resume_key had some NULL pointer
checks at the top. It turns out that at least one of those NULL
pointer checks is needed after all.

When the LastNameOffset in a FIND reply appears to be beyond the end of
the buffer, CIFSFindFirst and CIFSFindNext will set srch_inf.last_entry
to NULL. Since eaf35b1, the code will now oops in this situation.

Fix this by having the callers check for a NULL last entry pointer
before calling cifs_save_resume_key. No change is needed for the
call site in cifs_readdir as it's not reachable with a NULL
current_entry pointer.

This should fix:

    https://bugzilla.redhat.com/show_bug.cgi?id=750247

Cc: stable@vger.kernel.org
Cc: Christoph Hellwig <hch@infradead.org>
Reported-by: Adam G. Metzler <adamgmetzler@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

diff --git a/fs/cifs/readdir.c b/fs/cifs/readdir.c
index 5de03ec20144449c2dea66441b1e66cc577f4a48..a090bbe6ee29e196018867c9f5e4da3efe9d82b9 100644 (file)
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -554,7 +554,10 @@ static int find_cifs_entry(const int xid, struct cifs_tcon *pTcon,
                                 rc);
                        return rc;
                }
-               cifs_save_resume_key(cifsFile->srch_inf.last_entry, cifsFile);
+               /* FindFirst/Next set last_entry to NULL on malformed reply */
+               if (cifsFile->srch_inf.last_entry)
+                       cifs_save_resume_key(cifsFile->srch_inf.last_entry,
+                                               cifsFile);
        }
 
        while ((index_to_find >= cifsFile->srch_inf.index_of_last_entry) &&
@@ -562,7 +565,10 @@ static int find_cifs_entry(const int xid, struct cifs_tcon *pTcon,
                cFYI(1, "calling findnext2");
                rc = CIFSFindNext(xid, pTcon, cifsFile->netfid,
                                  &cifsFile->srch_inf);
-               cifs_save_resume_key(cifsFile->srch_inf.last_entry, cifsFile);
+               /* FindFirst/Next set last_entry to NULL on malformed reply */
+               if (cifsFile->srch_inf.last_entry)
+                       cifs_save_resume_key(cifsFile->srch_inf.last_entry,
+                                               cifsFile);
                if (rc)
                        return -ENOENT;
        }