Patch "fuse: break infinite loop in fuse_fill_write_pages()" has been added to the 3.10-stable tree

This is a note to let you know that I've just added the patch titled

fuse: break infinite loop in fuse_fill_write_pages()

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fuse-break-infinite-loop-in-fuse_fill_write_pages.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Roman Gushchin <[email protected]>
Date: Mon, 12 Oct 2015 16:33:44 +0300
Subject: fuse: break infinite loop in fuse_fill_write_pages()

From: Roman Gushchin <[email protected]>

commit 3ca8138f014a913f98e6ef40e939868e1e9ea876 upstream.

I got a report about unkillable task eating CPU. Further investigation shows, that the problem is in the fuse_fill_write_pages() function. If iov's first segment has zero length, we get an infinite loop, because we never reach iov_iter_advance() call.

Fix this by calling iov_iter_advance() before repeating an attempt to copy data from userspace.

A similar problem is described in 124d3b7041f ("fix writev regression:
pan hanging unkillable and un-straceable"). If zero-length segmend is followed by segment with invalid address, iov_iter_fault_in_readable() checks only first segment (zero-length), iov_iter_copy_from_user_atomic() skips it, fails at second and returns zero -> goto again without skipping zero-length segment.

Patch calls iov_iter_advance() before goto again: we'll skip zero-length segment at second iteraction and iov_iter_fault_in_readable() will detect invalid address.

Special thanks to Konstantin Khlebnikov, who helped a lot with the commit description.

---
 fs/fuse/file.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -993,6 +993,7 @@ static ssize_t fuse_fill_write_pages(str
 
 		mark_page_accessed(page);
 
+		iov_iter_advance(ii, tmp);
 		if (!tmp) {
 			unlock_page(page);
 			page_cache_release(page);

@@ -1005,7 +1006,6 @@ static ssize_t fuse_fill_write_pages(str
 		req->page_descs[req->num_pages].length = tmp;
 		req->num_pages++;
 
-		iov_iter_advance(ii, tmp);
 		count += tmp;
 		pos += tmp;
 		offset += tmp;

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/fuse-break-infinite-loop-in-fuse_fill_write_pages.patch