sync.c: add sanity check so we don't dereference a null pointer

Originally noticed in FS#9024, but was fixed in previous changes anyway.
However, it doesn't hurt to still check it.

Also add a pactest from Chantry Xavier for the original problem to ensure
we can't reproduce it.

Signed-off-by: Dan McGee <dan@archlinux.org>

1 files changed, 8 insertions, 6 deletions

diff --git a/lib/libalpm/sync.c b/lib/libalpm/sync.c
index dd54ce6c..ec4af9f4 100644
--- a/lib/libalpm/sync.c
+++ b/lib/libalpm/sync.c
@@ -570,12 +570,14 @@ int _alpm_sync_prepare(pmtrans_t *trans, pmdb_t *db_local, alpm_list_t *dbs_sync
 						}
 						if(rmpkg) {
 							pmsyncpkg_t *rsync = _alpm_sync_find(trans->packages, rmpkg);
-							void *vpkg;
-							_alpm_log(PM_LOG_DEBUG, "removing '%s' from target list\n",
-									rsync->pkg->name);
-							trans->packages = alpm_list_remove(trans->packages, rsync,
-									syncpkg_cmp, &vpkg);
-							_alpm_sync_free(vpkg);
+							if(rsync) {
+								void *vpkg;
+								_alpm_log(PM_LOG_DEBUG, "removing '%s' from target list\n",
+										rsync->pkg->name);
+								trans->packages = alpm_list_remove(trans->packages, rsync,
+										syncpkg_cmp, &vpkg);
+								_alpm_sync_free(vpkg);
+							}
 							continue;
 						}
 					}