Hmm.
There are *two* cases where we do that "total_remaining_bytes"
calculation. The same bug seems to exist both in ecryptfs_read() and
ecryptfs_write().
Possibly only the ecryptfs_write() one leads to an endless loop, but
the read one looks suspicious too.
Also, what protects things against this just being one nasty DoS
attack - even if the code is fixed to not be an endless loop, it looks
like a trivial "truncate()" can be used to generate a *practically*
infinite write stream. At the very least, this should be KILLABLE. Or
did I mis-read the code?
Tyler, Dustin, others - comments? This looks nasty.
Linus.
2012/1/17 dragonylffly <dragonylffly@xxxxxxx>:
> Hi,
> There is an infinite loop bug in eCryptfs, to make it present,
> just truncate to generate a huge file (>= 4G) on a 32-bit machine under
> the plain text foleder mounted with eCryptfs, a simple command
> 'truncate -s 4G dummy' is enough. Note: 4GB is smaller than 4G,
> therefore the following command 'truncate -s 4GB dummy' will not
> trigger this bug. The bug comes from a data overflow, the patch below fixes
> it.
>
> Cheers,
> Li Wang
>
> ---
>
> signed-off-by: Li Wang <liwang@xxxxxxxxxxx>
> Yunchuan Wen (wenyunchuan@xxxxxxxxxxxxxx)
>
> --- read_write.c.orig 2012-01-18 10:39:26.000000000 +0800
> +++ read_write.c 2012-01-18 19:48:41.484196221 +0800
> @@ -130,7 +130,7 @@
> pgoff_t ecryptfs_page_idx = (pos >> PAGE_CACHE_SHIFT);
> size_t start_offset_in_page = (pos & ~PAGE_CACHE_MASK);
> size_t num_bytes = (PAGE_CACHE_SIZE - start_offset_in_page);
> - size_t total_remaining_bytes = ((offset + size) - pos);
> + loff_t total_remaining_bytes = ((offset + size) - pos);
>
> if (num_bytes > total_remaining_bytes)
> num_bytes = total_remaining_bytes;
>
>
>
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