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>");
 }