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View File cgit-CVE-2013-2117-disallow-directory-traversal.patch of Package cgit (Project devel:tools:scm)

From babf94e04e74123eb658a823213c062663cdadd6 Mon Sep 17 00:00:00 2001
From: Jason A. Donenfeld <Jason@zx2c4.com>
Date: Sat, 25 May 2013 17:47:15 +0000
Subject: 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>
---
---
 ui-summary.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/ui-summary.c
+++ b/ui-summary.c
@@ -96,6 +96,7 @@ void cgit_print_repo_readme(char *path)
 	 * to the directory containing the configured readme.
 	 */
 	if (path) {
+		char *resolved_base, *resolved_full;
 		slash = strrchr(ctx.repo->readme, '/');
 		if (!slash) {
 			if (!colon)
@@ -104,7 +105,19 @@ void cgit_print_repo_readme(char *path)
 		}
 		tmp = xmalloc(slash - ctx.repo->readme + 1 + strlen(path) + 1);
 		strncpy(tmp, ctx.repo->readme, slash - ctx.repo->readme + 1);
+		if (!ref)
+			resolved_base = realpath(tmp, NULL);
 		strcpy(tmp + (slash - ctx.repo->readme + 1), path);
+		if (!ref) {
+			resolved_full = realpath(tmp, NULL);
+			if (!resolved_base || !resolved_full ||
+			    strstr(resolved_full, resolved_base) != resolved_full) {
+				free(tmp);
+				return;
+			}
+			free(resolved_base);
+			free(resolved_full);
+		}
 	} else
 		tmp = ctx.repo->readme;