Fix segfaults on opening invalid archive files

"invalid" in this case simply means files that may or may not be
archives. Discovered via a `pacman -Sc` operation with delta files in
the package cache directory, but can be triggered if any file is passed
to `pacman -Ql` that isn't an archive, for instance, or if the sync
database file is not an archive.

Fix it up so we are more careful about calling archive_read_finish()
only on archives that are valid and have not already been closed, and
teach our archive open function to set the returned archive to NULL if
we aren't going to be returning something valid anyway.

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

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/libalpm/be_sync.c b/lib/libalpm/be_sync.c
index b16271bc..c4673b1b 100644
--- a/lib/libalpm/be_sync.c
+++ b/lib/libalpm/be_sync.c
@@ -391,7 +391,7 @@ static int sync_db_populate(alpm_db_t *db)
 {
 	const char *dbpath;
 	size_t est_count;
-	int count = -1, fd;
+	int count, fd;
 	struct stat buf;
 	struct archive *archive;
 	struct archive_entry *entry;
@@ -412,13 +412,14 @@ static int sync_db_populate(alpm_db_t *db)
 	fd = _alpm_open_archive(db->handle, dbpath, &buf,
 			&archive, ALPM_ERR_DB_OPEN);
 	if(fd < 0) {
-		goto cleanup;
+		return -1;
 	}
 	est_count = estimate_package_count(&buf, archive);
 
 	db->pkgcache = _alpm_pkghash_create(est_count);
 	if(db->pkgcache == NULL) {
 		db->handle->pm_errno = ALPM_ERR_MEMORY;
+		count = -1;
 		goto cleanup;
 	}