https://github.com/git/git
Revision 0383bbb9015898cbc79abd7b64316484d7713b44 authored by Jeff King on 30 April 2018, 07:25:25 UTC, committed by Jeff King on 22 May 2018, 03:50:11 UTC
Submodule "names" come from the untrusted .gitmodules file, but we blindly append them to $GIT_DIR/modules to create our on-disk repo paths. This means you can do bad things by putting "../" into the name (among other things). Let's sanity-check these names to avoid building a path that can be exploited. There are two main decisions: 1. What should the allowed syntax be? It's tempting to reuse verify_path(), since submodule names typically come from in-repo paths. But there are two reasons not to: a. It's technically more strict than what we need, as we really care only about breaking out of the $GIT_DIR/modules/ hierarchy. E.g., having a submodule named "foo/.git" isn't actually dangerous, and it's possible that somebody has manually given such a funny name. b. Since we'll eventually use this checking logic in fsck to prevent downstream repositories, it should be consistent across platforms. Because verify_path() relies on is_dir_sep(), it wouldn't block "foo\..\bar" on a non-Windows machine. 2. Where should we enforce it? These days most of the .gitmodules reads go through submodule-config.c, so I've put it there in the reading step. That should cover all of the C code. We also construct the name for "git submodule add" inside the git-submodule.sh script. This is probably not a big deal for security since the name is coming from the user anyway, but it would be polite to remind them if the name they pick is invalid (and we need to expose the name-checker to the shell anyway for our test scripts). This patch issues a warning when reading .gitmodules and just ignores the related config entry completely. This will generally end up producing a sensible error, as it works the same as a .gitmodules file which is missing a submodule entry (so "submodule update" will barf, but "git clone --recurse-submodules" will print an error but not abort the clone. There is one minor oddity, which is that we print the warning once per malformed config key (since that's how the config subsystem gives us the entries). So in the new test, for example, the user would see three warnings. That's OK, since the intent is that this case should never come up outside of malicious repositories (and then it might even benefit the user to see the message multiple times). Credit for finding this vulnerability and the proof of concept from which the test script was adapted goes to Etienne Stalmans. Signed-off-by: Jeff King <peff@peff.net>
1 parent 42e6fde
Tip revision: 0383bbb9015898cbc79abd7b64316484d7713b44 authored by Jeff King on 30 April 2018, 07:25:25 UTC
submodule-config: verify submodule names as paths
submodule-config: verify submodule names as paths
Tip revision: 0383bbb
replace_object.c
#include "cache.h"
#include "sha1-lookup.h"
#include "refs.h"
#include "commit.h"
/*
* An array of replacements. The array is kept sorted by the original
* sha1.
*/
static struct replace_object {
unsigned char original[20];
unsigned char replacement[20];
} **replace_object;
static int replace_object_alloc, replace_object_nr;
static const unsigned char *replace_sha1_access(size_t index, void *table)
{
struct replace_object **replace = table;
return replace[index]->original;
}
static int replace_object_pos(const unsigned char *sha1)
{
return sha1_pos(sha1, replace_object, replace_object_nr,
replace_sha1_access);
}
static int register_replace_object(struct replace_object *replace,
int ignore_dups)
{
int pos = replace_object_pos(replace->original);
if (0 <= pos) {
if (ignore_dups)
free(replace);
else {
free(replace_object[pos]);
replace_object[pos] = replace;
}
return 1;
}
pos = -pos - 1;
ALLOC_GROW(replace_object, replace_object_nr + 1, replace_object_alloc);
replace_object_nr++;
if (pos < replace_object_nr)
memmove(replace_object + pos + 1,
replace_object + pos,
(replace_object_nr - pos - 1) *
sizeof(*replace_object));
replace_object[pos] = replace;
return 0;
}
static int register_replace_ref(const char *refname,
const struct object_id *oid,
int flag, void *cb_data)
{
/* Get sha1 from refname */
const char *slash = strrchr(refname, '/');
const char *hash = slash ? slash + 1 : refname;
struct replace_object *repl_obj = xmalloc(sizeof(*repl_obj));
if (strlen(hash) != 40 || get_sha1_hex(hash, repl_obj->original)) {
free(repl_obj);
warning("bad replace ref name: %s", refname);
return 0;
}
/* Copy sha1 from the read ref */
hashcpy(repl_obj->replacement, oid->hash);
/* Register new object */
if (register_replace_object(repl_obj, 1))
die("duplicate replace ref: %s", refname);
return 0;
}
static void prepare_replace_object(void)
{
static int replace_object_prepared;
if (replace_object_prepared)
return;
for_each_replace_ref(register_replace_ref, NULL);
replace_object_prepared = 1;
if (!replace_object_nr)
check_replace_refs = 0;
}
/* We allow "recursive" replacement. Only within reason, though */
#define MAXREPLACEDEPTH 5
/*
* If a replacement for object sha1 has been set up, return the
* replacement object's name (replaced recursively, if necessary).
* The return value is either sha1 or a pointer to a
* permanently-allocated value. This function always respects replace
* references, regardless of the value of check_replace_refs.
*/
const unsigned char *do_lookup_replace_object(const unsigned char *sha1)
{
int pos, depth = MAXREPLACEDEPTH;
const unsigned char *cur = sha1;
prepare_replace_object();
/* Try to recursively replace the object */
do {
if (--depth < 0)
die("replace depth too high for object %s",
sha1_to_hex(sha1));
pos = replace_object_pos(cur);
if (0 <= pos)
cur = replace_object[pos]->replacement;
} while (0 <= pos);
return cur;
}
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