g10: Fix double free when locating by mbox

* g10/getkey.c (get_best_pubkey_byname): Set new.uid always
to NULL after use.

--
pubkey_cmp is not guranteed to set new.uid.
So if the diff < 0 case is reached best is set to new.

If then diff > 0 is reached without modifying new.uid
e.g. if the key has no matching mboxes. new.uid is
free'd even though the uid is still referenced in
best.

GnuPG-Bug-Id: T4462
(cherry picked from commit e57954ed278cb5e6e725005b1ecaf7ce70006ce0)

1 files changed, 1 insertions, 2 deletions

diff --git a/g10/getkey.c b/g10/getkey.c
index c4afe4510..1b699a411 100644
--- a/g10/getkey.c
+++ b/g10/getkey.c
@@ -1495,15 +1495,14 @@ get_best_pubkey_byname (ctrl_t ctrl, GETKEY_CTX *retctx, PKT_public_key *pk,
               /* Old key is better.  */
               release_public_key_parts (&new.key);
               free_user_id (new.uid);
-              new.uid = NULL;
             }
           else
             {
               /* A tie.  Keep the old key.  */
               release_public_key_parts (&new.key);
               free_user_id (new.uid);
-              new.uid = NULL;
             }
+          new.uid = NULL;
         }
       getkey_end (ctrl, ctx);
       ctx = NULL;