On Sat, Jul 06, 2013 at 09:48:52PM +0200, Michael Haggerty wrote:
> When and if resolve_symlink() is called, then that function is
> correctly told to treat the buffer as (PATH_MAX - 5) characters long.
> This part is correct. However:
>
> * If LOCK_NODEREF was specified, then resolve_symlink() is never
> called.
>
> * If resolve_symlink() is called but the path is not a symlink, then
> the length check is never applied.
>
> So it is possible for a path with length (PATH_MAX - 5 <= len <
> PATH_MAX) to make it through the checks. When ".lock" is strcat()ted
> to such a path, the lock_file::filename buffer is overflowed.
Thanks for posting this. I independently discovered this about a month
ago while working on an unrelated series, and then let it languish
unseen and forgotten at the base of that almost-done series.
So definitely a problem, and my patch looked almost identical to
yours. The only difference is:
> static int lock_file(struct lock_file *lk, const char *path, int flags)
> {
> - if (strlen(path) >= sizeof(lk->filename))
> - return -1;
> - strcpy(lk->filename, path);
> /*
> * subtract 5 from size to make sure there's room for adding
> * ".lock" for the lock file name
> */
> + if (strlen(path) >= sizeof(lk->filename)-5)
> + return -1;
> + strcpy(lk->filename, path);
> if (!(flags & LOCK_NODEREF))
> resolve_symlink(lk->filename, sizeof(lk->filename)-5);
It might be worth consolidating the magic "-5" into a constant near the
comment, like this:
diff --git a/lockfile.c b/lockfile.c
index c6fb77b..2aeb2bb 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -124,15 +124,16 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
static int lock_file(struct lock_file *lk, const char *path, int flags)
{
- if (strlen(path) >= sizeof(lk->filename))
- return -1;
- strcpy(lk->filename, path);
/*
* subtract 5 from size to make sure there's room for adding
* ".lock" for the lock file name
*/
+ static const size_t max_path_len = sizeof(lk->filename) - 5;
+ if (strlen(path) >= max_path_len)
+ return -1;
+ strcpy(lk->filename, path);
if (!(flags & LOCK_NODEREF))
- resolve_symlink(lk->filename, sizeof(lk->filename)-5);
+ resolve_symlink(lk->filename, max_path_len);
strcat(lk->filename, ".lock");
lk->fd = open(lk->filename, O_RDWR | O_CREAT | O_EXCL, 0666);
if (0 <= lk->fd) {
But either way, the fix looks good to me.
-Peff
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