fuse: break infinite loop in fuse_fill_write_pages()
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.
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Maxim Patlasov <mpatlasov@parallels.com>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Roman Gushchin <klamm@yandex-team.ru>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Fixes: ea9b9907b82a ("fuse: implement perform_write")
Cc: <stable@vger.kernel.org>
Conflicts:
fs/fuse/file.c
Change-Id: Id37193373294dd43191469389cfe68ca1736a54b
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 33dd5cc..9c545ef 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -901,6 +901,7 @@
mark_page_accessed(page);
+ iov_iter_advance(ii, tmp);
if (!tmp) {
unlock_page(page);
page_cache_release(page);
@@ -912,7 +913,6 @@
req->pages[req->num_pages] = page;
req->num_pages++;
- iov_iter_advance(ii, tmp);
count += tmp;
pos += tmp;
offset += tmp;