Avoid SEGFAULT on invalid requests

When an unknown page is requested, either on the querystring or via
PATH_INFO, we end up with a null-referencing cgit_cmd. This null-
pointer is then used as argument to the hc() function (which decides
what tab to render as 'active'), but this function failed to check if a
valid cmd was specified and a SEGFAULT would occur. This patch fixes the
issue by introducing a 'fallback-cmd' which specifies what tab to render
as 'active' when no valid cmd is requested.

While at it, we now also keep track of the active repository even if an
invalid cmd was requested since we want to show the error message about
the invalid request in the correct context.

Noticed-by: Robin Redeker <elmex@ta-sa.org>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

2 files changed, 6 insertions, 2 deletions

diff --git a/cgit.c b/cgit.c
index c82587b..6e5215e 100644
--- a/cgit.c
+++ b/cgit.c
@@ -244,97 +244,96 @@ static int prepare_repo_cmd(struct cgit_context *ctx)
                                       "config error");
                 tmp = fmt("Not a git repository: '%s'", ctx->repo->path);
                 ctx->repo = NULL;
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error(tmp);
                 cgit_print_docend();
                 return 1;
         }
         ctx->page.title = fmt("%s - %s", ctx->repo->name, ctx->repo->desc);
 
         if (!ctx->qry.head) {
                 ctx->qry.nohead = 1;
                 ctx->qry.head = find_default_branch(ctx->repo);
                 ctx->repo->defbranch = ctx->qry.head;
         }
 
         if (!ctx->qry.head) {
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error("Repository seems to be empty");
                 cgit_print_docend();
                 return 1;
         }
 
         if (get_sha1(ctx->qry.head, sha1)) {
                 tmp = xstrdup(ctx->qry.head);
                 ctx->qry.head = ctx->repo->defbranch;
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error(fmt("Invalid branch: %s", tmp));
                 cgit_print_docend();
                 return 1;
         }
         return 0;
 }
 
 static void process_request(void *cbdata)
 {
         struct cgit_context *ctx = cbdata;
         struct cgit_cmd *cmd;
 
         cmd = cgit_get_cmd(ctx);
         if (!cmd) {
                 ctx->page.title = "cgit error";
-                ctx->repo = NULL;
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error("Invalid request");
                 cgit_print_docend();
                 return;
         }
 
         if (cmd->want_repo && !ctx->repo) {
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
                 cgit_print_error(fmt("No repository selected"));
                 cgit_print_docend();
                 return;
         }
 
         if (ctx->repo && prepare_repo_cmd(ctx))
                 return;
 
         if (cmd->want_layout) {
                 cgit_print_http_headers(ctx);
                 cgit_print_docstart(ctx);
                 cgit_print_pageheader(ctx);
         }
 
         cmd->fn(ctx);
 
         if (cmd->want_layout)
                 cgit_print_docend();
 }
 
 int cmp_repos(const void *a, const void *b)
 {
         const struct cgit_repo *ra = a, *rb = b;
         return strcmp(ra->url, rb->url);
 }
 
 void print_repo(struct cgit_repo *repo)
 {
         printf("repo.url=%s\n", repo->url);
         printf("repo.name=%s\n", repo->name);
         printf("repo.path=%s\n", repo->path);
         if (repo->owner)
                 printf("repo.owner=%s\n", repo->owner);
         if (repo->desc)
                 printf("repo.desc=%s\n", repo->desc);
         if (repo->readme)
diff --git a/ui-shared.c b/ui-shared.c
index 224e5f3..76cd00d 100644
--- a/ui-shared.c
+++ b/ui-shared.c
@@ -532,105 +532,110 @@ int print_archive_ref(const char *refname, const unsigned char *sha1,
                         return 0;
                 hashcpy(fileid, tag->tagged->sha1);
         } else if (obj->type != OBJ_BLOB) {
                 return 0;
         } else {
                 hashcpy(fileid, sha1);
         }
         if (!*header) {
                 html("<h1>download</h1>\n");
                 *header = 1;
         }
         url = cgit_pageurl(ctx.qry.repo, "blob",
                            fmt("id=%s&amp;path=%s", sha1_to_hex(fileid),
                                buf));
         html_link_open(url, NULL, "menu");
         html_txt(strlpart(buf, 20));
         html_link_close();
         return 0;
 }
 
 void add_hidden_formfields(int incl_head, int incl_search, char *page)
 {
         char *url;
 
         if (!ctx.cfg.virtual_root) {
                 url = fmt("%s/%s", ctx.qry.repo, page);
                 if (ctx.qry.path)
                         url = fmt("%s/%s", url, ctx.qry.path);
                 html_hidden("url", url);
         }
 
         if (incl_head && ctx.qry.head && ctx.repo->defbranch &&
             strcmp(ctx.qry.head, ctx.repo->defbranch))
                 html_hidden("h", ctx.qry.head);
 
         if (ctx.qry.sha1)
                 html_hidden("id", ctx.qry.sha1);
         if (ctx.qry.sha2)
                 html_hidden("id2", ctx.qry.sha2);
 
         if (incl_search) {
                 if (ctx.qry.grep)
                         html_hidden("qt", ctx.qry.grep);
                 if (ctx.qry.search)
                         html_hidden("q", ctx.qry.search);
         }
 }
 
+const char *fallback_cmd = "repolist";
+
 char *hc(struct cgit_cmd *cmd, const char *page)
 {
-        return (strcmp(cmd->name, page) ? NULL : "active");
+        return (strcmp(cmd ? cmd->name : fallback_cmd, page) ? NULL : "active");
 }
 
 void cgit_print_pageheader(struct cgit_context *ctx)
 {
         struct cgit_cmd *cmd = cgit_get_cmd(ctx);
 
+        if (!cmd && ctx->repo)
+                fallback_cmd = "summary";
+
         html("<table id='header'>\n");
         html("<tr>\n");
         html("<td class='logo' rowspan='2'><a href='");
         if (ctx->cfg.logo_link)
                 html_attr(ctx->cfg.logo_link);
         else
                 html_attr(cgit_rooturl());
         html("'><img src='");
         html_attr(ctx->cfg.logo);
         html("' alt='cgit logo'/></a></td>\n");
 
         html("<td class='main'>");
         if (ctx->repo) {
                 cgit_index_link("index", NULL, NULL, NULL, 0);
                 html(" : ");
                 cgit_summary_link(ctx->repo->name, ctx->repo->name, NULL, NULL);
                 html("</td><td class='form'>");
                 html("<form method='get' action=''>\n");
                 add_hidden_formfields(0, 1, ctx->qry.page);
                 html("<select name='h' onchange='this.form.submit();'>\n");
                 for_each_branch_ref(print_branch_option, ctx->qry.head);
                 html("</select> ");
                 html("<input type='submit' name='' value='switch'/>");
                 html("</form>");
         } else
                 html_txt(ctx->cfg.root_title);
         html("</td></tr>\n");
 
         html("<tr><td class='sub'>");
         if (ctx->repo) {
                 html_txt(ctx->repo->desc);
                 html("</td><td class='sub right'>");
                 html_txt(ctx->repo->owner);
         } else {
                 if (ctx->cfg.root_desc)
                         html_txt(ctx->cfg.root_desc);
                 else if (ctx->cfg.index_info)
                         html_include(ctx->cfg.index_info);
         }
         html("</td></tr></table>\n");
 
         html("<table class='tabs'><tr><td>\n");
         if (ctx->repo) {
                 cgit_summary_link("summary", NULL, hc(cmd, "summary"),
                                   ctx->qry.head);
                 cgit_refs_link("refs", NULL, hc(cmd, "refs"), ctx->qry.head,
                                ctx->qry.sha1, NULL);
                 cgit_log_link("log", NULL, hc(cmd, "log"), ctx->qry.head,