ui-summary: Disallow directory traversal
Using the url= query string, it was possible request arbitrary files
from the filesystem if the readme for a given page was set to a
filesystem file. The following request would return my /etc/passwd file:
http://git.zx2c4.com/?url=/somerepo/about/../../../../etc/passwd
http://data.zx2c4.com/cgit-directory-traversal.png
This fix uses realpath(3) to canonicalize all paths, and then compares
the base components.
This fix introduces a subtle timing attack, whereby a client can check
whether or not strstr is called using timing measurements in order
to determine if a given file exists on the filesystem.
This fix also does not account for filesystem race conditions (TOCTOU)
in resolving symlinks.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
diff --git a/ui-summary.c b/ui-summary.c
index 2f8a822..57206dd 100644
--- a/ui-summary.c
+++ b/ui-summary.c
@@ -99,6 +99,7 @@
void cgit_parse_readme(const char *readme, const char *path, char **filename, char **ref, struct cgit_repo *repo)
{
const char *slash, *colon;
+ char *resolved_base, *resolved_full;
*filename = NULL;
*ref = NULL;
@@ -133,7 +134,19 @@
}
*filename = xmalloc(slash - readme + 1 + strlen(path) + 1);
strncpy(*filename, readme, slash - readme + 1);
+ if (!(*ref))
+ resolved_base = realpath(*filename, NULL);
strcpy(*filename + (slash - readme + 1), path);
+ if (!(*ref))
+ resolved_full = realpath(*filename, NULL);
+ if (!(*ref) && (!resolved_base || !resolved_full || strstr(resolved_full, resolved_base) != resolved_full)) {
+ free(*filename);
+ *filename = NULL;
+ }
+ if (!(*ref)) {
+ free(resolved_base);
+ free(resolved_full);
+ }
} else
*filename = xstrdup(readme);
}
@@ -143,6 +156,9 @@
char *filename, *ref;
cgit_parse_readme(ctx.repo->readme, path, &filename, &ref, ctx.repo);
+ if (!filename)
+ return;
+
/* Print the calculated readme, either from the git repo or from the
* filesystem, while applying the about-filter.
*/
