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SubjectRe: fs: out of bounds on stack in iov_iter_advance
On 08/19/2015 01:46 AM, Al Viro wrote:
> On Mon, Aug 17, 2015 at 12:18:12PM +0300, Andrey Ryabinin wrote:
>
>> This bug is similar to recently found bug in 9p: http://thread.gmane.org/gmane.linux.kernel/1931799/focus=1936542
>
> Ow. For those who'd missed that fun: the bug in question had turned out to
> be caused by improper reuse of request ids, _not_ in the call chain of
> the triggering syscall.
>
>> if (!retval) {
>> struct iov_iter data = *iter;
>> retval = mapping->a_ops->direct_IO(iocb, &data, pos);
>> }
>>
>> if (retval > 0) {
>> *ppos = pos + retval;
>> iov_iter_advance(iter, retval);
>>
>>
>> So either filemap_write_and_wait_range()
> Shouldn't - it's supposed to return 0 or -E...
>
>> or mapping->a_ops->direct_IO() returned more
>> than 'count'.
>
> Was there DAX involved? ->direct_IO() in there is blkdev_direct_IO(),
> which takes rather different paths in those cases...

I don't think so, at least I didn't configure it in.

>>> Also too the file and line number
>>> (lib/iov_iter.c:511) are completely useless because of inlining,
>>> though that's not kasan's fault.
>
> Might make sense to slap
> if (WARN_ON(size > iov_iter_count(i)))
> print size and *i
> and see if it triggers...

It finally reproduced. size == 0x1000000, iov_iter_count(iter) == 0x1234.


Thanks,
Sasha



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