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ui-summary: Disallow directory traversal

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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>
This commit is contained in:
Jason A. Donenfeld 2013-05-25 19:47:15 +02:00
parent 2a1ead3efb
commit fe36f84d84
1 changed files with 16 additions and 0 deletions
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16
ui-summary.c
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@ -99,6 +99,7 @@ void cgit_print_summary()
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 @@ void cgit_parse_readme(const char *readme, const char *path, char **filename, ch
}
*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 @@ void cgit_print_repo_readme(char *path)
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.
*/