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>

2 files changed, 34 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;
 						}
 					}
diff --git a/pactest/tests/sync404.py b/pactest/tests/sync404.py
new file mode 100644
index 00000000..118f9e9d
--- /dev/null
+++ b/pactest/tests/sync404.py
@@ -0,0 +1,26 @@
+self.description = "FS#9024"
+
+sp = pmpkg("xorg-server")
+sp.depends = [ "libgl" ]
+self.addpkg2db("sync", sp)
+
+sp1 = pmpkg("nvidia-utils")
+sp1.provides = [ "libgl" ]
+sp1.conflicts = [ "libgl", "libgl-dri" ]
+self.addpkg2db("sync", sp1)
+
+sp2 = pmpkg("libgl")
+sp2.provides = [ "libgl-dri" ]
+self.addpkg2db("sync", sp2)
+
+sp3 = pmpkg("nvidia")
+sp3.depends = [ "nvidia-utils" ]
+self.addpkg2db("sync", sp3)
+
+self.args = "-S xorg-server nvidia"
+
+self.addrule("PACMAN_RETCODE=0")
+self.addrule("PKG_EXIST=xorg-server")
+self.addrule("PKG_EXIST=nvidia")
+self.addrule("PKG_EXIST=nvidia-utils")
+self.addrule("!PKG_EXIST=libgl")