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unique_path: fix unlikely heap overflow

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When merge-recursive creates a unique filename, it uses a
template like:

  path~branch_%d

where the final "_%d" is filled by an incrementing counter
until we find a unique name. We allocate 8 characters for
the counter, but there is no logic to limit the size of the
integer.

Of course, this is extremely unlikely, as you would need a
hundred million collisions to trigger the problem.  Even if
an attacker constructed a specialized repo, it is unlikely
that the victim would have the patience to run the merge.

However, we can make it trivially correct (and hopefully
more readable) by using a strbuf.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff King 2014-06-19 17:30:26 -04:00 committed by Junio C Hamano
parent f33206992d
commit 45bc131dd3
1 changed files with 25 additions and 14 deletions
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39
merge-recursive.c
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@ -601,25 +601,36 @@ static int remove_file(struct merge_options *o, int clean,
return 0;
}
/* add a string to a strbuf, but converting "/" to "_" */
static void add_flattened_path(struct strbuf *out, const char *s)
{
size_t i = out->len;
strbuf_addstr(out, s);
for (; i < out->len; i++)
if (out->buf[i] == '/')
out->buf[i] = '_';
}
static char *unique_path(struct merge_options *o, const char *path, const char *branch)
{
char *newpath = xmalloc(strlen(path) + 1 + strlen(branch) + 8 + 1);
struct strbuf newpath = STRBUF_INIT;
int suffix = 0;
struct stat st;
char *p = newpath + strlen(path);
strcpy(newpath, path);
*(p++) = '~';
strcpy(p, branch);
for (; *p; ++p)
if ('/' == *p)
*p = '_';
while (string_list_has_string(&o->current_file_set, newpath) ||
string_list_has_string(&o->current_directory_set, newpath) ||
lstat(newpath, &st) == 0)
sprintf(p, "_%d", suffix++);
size_t base_len;
string_list_insert(&o->current_file_set, newpath);
return newpath;
strbuf_addf(&newpath, "%s~", path);
add_flattened_path(&newpath, branch);
base_len = newpath.len;
while (string_list_has_string(&o->current_file_set, newpath.buf) ||
string_list_has_string(&o->current_directory_set, newpath.buf) ||
lstat(newpath.buf, &st) == 0) {
strbuf_setlen(&newpath, base_len);
strbuf_addf(&newpath, "_%d", suffix++);
}
string_list_insert(&o->current_file_set, newpath.buf);
return strbuf_detach(&newpath, NULL);
}
static int dir_in_way(const char *path, int check_working_copy)