ui-tag.c: do not segfault when id is missing from query-string

The purpose of the tag page is to print info about a specific tag,
but if no tag was specified on the query-string cgit used to segfault.

With this patch, cgit will fallback to the value of the 'h' parameter
instead (which is never NULL due to prepare_repo_cmd() in cgit.c).

It will now also verify that the specified tagname is in fact a valid
ref in the 'refs/tags/' namespace, i.e. specifying 'id=master' will
trigger a 'Bad tag reference' error.

Noticed-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/ui-tag.c b/ui-tag.c
index 0e056e0..8c263ab 100644
--- a/ui-tag.c
+++ b/ui-tag.c
@@ -8,65 +8,68 @@
 
 #include "cgit.h"
 #include "html.h"
 #include "ui-shared.h"
 
 static void print_tag_content(char *buf)
 {
 	char *p;
 
 	if (!buf)
 		return;
 
 	html("<div class='commit-subject'>");
 	p = strchr(buf, '\n');
 	if (p)
 		*p = '\0';
 	html_txt(buf);
 	html("</div>");
 	if (p) {
 		html("<div class='commit-msg'>");
 		html_txt(++p);
 		html("</div>");
 	}
 }
 
 void cgit_print_tag(char *revname)
 {
 	unsigned char sha1[20];
 	struct object *obj;
 	struct tag *tag;
 	struct taginfo *info;
 
-	if (get_sha1(revname, sha1)) {
+	if (!revname)
+		revname = ctx.qry.head;
+
+	if (get_sha1(fmt("refs/tags/%s", revname), sha1)) {
 		cgit_print_error(fmt("Bad tag reference: %s", revname));
 		return;
 	}
 	obj = parse_object(sha1);
 	if (!obj) {
 		cgit_print_error(fmt("Bad object id: %s", sha1_to_hex(sha1)));
 		return;
 	}
 	if (obj->type == OBJ_TAG) {
 		tag = lookup_tag(sha1);
 		if (!tag || parse_tag(tag) || !(info = cgit_parse_tag(tag))) {
 			cgit_print_error(fmt("Bad tag object: %s", revname));
 			return;
 		}
 		html("<table class='commit-info'>\n");
 		htmlf("<tr><td>Tag name</td><td>");
 		html_txt(revname);
 		htmlf(" (%s)</td></tr>\n", sha1_to_hex(sha1));
 		if (info->tagger_date > 0) {
 			html("<tr><td>Tag date</td><td>");
 			cgit_print_date(info->tagger_date, FMT_LONGDATE, ctx.cfg.local_time);
 			html("</td></tr>\n");
 		}
 		if (info->tagger) {
 			html("<tr><td>Tagged by</td><td>");
 			html_txt(info->tagger);
 			if (info->tagger_email) {
 				html(" ");
 				html_txt(info->tagger_email);
 			}
 			html("</td></tr>\n");
 		}