Avoid null pointer dereference in cgit_print_diff().

When calling cgit_print_diff() with a bad new_rev and a NULL old_rev,
checking for new_rev's parent commit will result in a null pointer
dereference. Returning on an invalid commit before dereferencing fixes
this. Spotted with clang-analyzer.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/ui-diff.c b/ui-diff.c
index a7bc667..d21541b 100644
--- a/ui-diff.c
+++ b/ui-diff.c
@@ -336,43 +336,47 @@ void cgit_print_diff(const char *new_rev, const char *old_rev, const char *prefi
 	unsigned long size;
 	struct commit *commit, *commit2;
 
 	if (!new_rev)
 		new_rev = ctx.qry.head;
 	get_sha1(new_rev, new_rev_sha1);
 	type = sha1_object_info(new_rev_sha1, &size);
 	if (type == OBJ_BAD) {
 		cgit_print_error(fmt("Bad object name: %s", new_rev));
 		return;
 	}
 	commit = lookup_commit_reference(new_rev_sha1);
-	if (!commit || parse_commit(commit))
+	if (!commit || parse_commit(commit)) {
 		cgit_print_error(fmt("Bad commit: %s", sha1_to_hex(new_rev_sha1)));
+		return;
+	}
 
 	if (old_rev)
 		get_sha1(old_rev, old_rev_sha1);
 	else if (commit->parents && commit->parents->item)
 		hashcpy(old_rev_sha1, commit->parents->item->object.sha1);
 	else
 		hashclr(old_rev_sha1);
 
 	if (!is_null_sha1(old_rev_sha1)) {
 		type = sha1_object_info(old_rev_sha1, &size);
 		if (type == OBJ_BAD) {
 			cgit_print_error(fmt("Bad object name: %s", sha1_to_hex(old_rev_sha1)));
 			return;
 		}
 		commit2 = lookup_commit_reference(old_rev_sha1);
-		if (!commit2 || parse_commit(commit2))
+		if (!commit2 || parse_commit(commit2)) {
 			cgit_print_error(fmt("Bad commit: %s", sha1_to_hex(old_rev_sha1)));
+			return;
+		}
 	}
 
 	if ((ctx.qry.ssdiff && !ctx.cfg.ssdiff) || (!ctx.qry.ssdiff && ctx.cfg.ssdiff))
 		use_ssdiff = 1;
 
 	print_ssdiff_link();
 	cgit_print_diffstat(old_rev_sha1, new_rev_sha1, prefix);
 
 	if (use_ssdiff) {
 		html("<table summary='ssdiff' class='ssdiff'>");
 	} else {
 		html("<table summary='diff' class='diff'>");