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
@@ -252,135 +252,139 @@ static void header(unsigned char *sha1, char *path1, int mode1,
 		htmlf("<br/>deleted file mode %.6o", mode1);
 
 	if (!subproject) {
 		abbrev1 = xstrdup(find_unique_abbrev(sha1, DEFAULT_ABBREV));
 		abbrev2 = xstrdup(find_unique_abbrev(sha2, DEFAULT_ABBREV));
 		htmlf("<br/>index %s..%s", abbrev1, abbrev2);
 		free(abbrev1);
 		free(abbrev2);
 		if (mode1 != 0 && mode2 != 0) {
 			htmlf(" %.6o", mode1);
 			if (mode2 != mode1)
 				htmlf("..%.6o", mode2);
 		}
 		html("<br/>--- a/");
 		if (mode1 != 0)
 			cgit_tree_link(path1, NULL, NULL, ctx.qry.head,
 				       sha1_to_hex(old_rev_sha1), path1);
 		else
 			html_txt(path1);
 		html("<br/>+++ b/");
 		if (mode2 != 0)
 			cgit_tree_link(path2, NULL, NULL, ctx.qry.head,
 				       sha1_to_hex(new_rev_sha1), path2);
 		else
 			html_txt(path2);
 	}
 	html("</div>");
 }
 
 static void print_ssdiff_link()
 {
 	if (!strcmp(ctx.qry.page, "diff")) {
 		if (use_ssdiff)
 			cgit_diff_link("Unidiff", NULL, NULL, ctx.qry.head,
 				       ctx.qry.sha1, ctx.qry.sha2, ctx.qry.path, 1);
 		else
 			cgit_diff_link("Side-by-side diff", NULL, NULL,
 				       ctx.qry.head, ctx.qry.sha1,
 				       ctx.qry.sha2, ctx.qry.path, 1);
 	}
 }
 
 static void filepair_cb(struct diff_filepair *pair)
 {
 	unsigned long old_size = 0;
 	unsigned long new_size = 0;
 	int binary = 0;
 	linediff_fn print_line_fn = print_line;
 
 	current_filepair = pair;
 	if (use_ssdiff) {
 		cgit_ssdiff_header_begin();
 		print_line_fn = cgit_ssdiff_line_cb;
 	}
 	header(pair->one->sha1, pair->one->path, pair->one->mode,
 	       pair->two->sha1, pair->two->path, pair->two->mode);
 	if (use_ssdiff)
 		cgit_ssdiff_header_end();
 	if (S_ISGITLINK(pair->one->mode) || S_ISGITLINK(pair->two->mode)) {
 		if (S_ISGITLINK(pair->one->mode))
 			print_line_fn(fmt("-Subproject %s", sha1_to_hex(pair->one->sha1)), 52);
 		if (S_ISGITLINK(pair->two->mode))
 			print_line_fn(fmt("+Subproject %s", sha1_to_hex(pair->two->sha1)), 52);
 		if (use_ssdiff)
 			cgit_ssdiff_footer();
 		return;
 	}
 	if (cgit_diff_files(pair->one->sha1, pair->two->sha1, &old_size,
 			    &new_size, &binary, ctx.qry.context,
 			    ctx.qry.ignorews, print_line_fn))
 		cgit_print_error("Error running diff");
 	if (binary) {
 		if (use_ssdiff)
 			html("<tr><td colspan='4'>Binary files differ</td></tr>");
 		else
 			html("Binary files differ");
 	}
 	if (use_ssdiff)
 		cgit_ssdiff_footer();
 }
 
 void cgit_print_diff(const char *new_rev, const char *old_rev, const char *prefix)
 {
 	enum object_type type;
 	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'>");
 		html("<tr><td>");
 	}
 	cgit_diff_tree(old_rev_sha1, new_rev_sha1, filepair_cb, prefix,
 		       ctx.qry.ignorews);
 	if (!use_ssdiff)
 		html("</td></tr>");
 	html("</table>");
 }