Skip to content

Commit 3ca8138

Browse files
Roman Gushchinszmi
Roman Gushchin
authored andcommitted
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 124d3b7 ("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: ea9b990 ("fuse: implement perform_write") Cc: <stable@vger.kernel.org>
1 parent 2c5816b commit 3ca8138

File tree

1 file changed

+1
-1
lines changed

1 file changed

+1
-1
lines changed

Diff for: fs/fuse/file.c

+1-1
Original file line numberDiff line numberDiff line change
@@ -1049,6 +1049,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
10491049
tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
10501050
flush_dcache_page(page);
10511051

1052+
iov_iter_advance(ii, tmp);
10521053
if (!tmp) {
10531054
unlock_page(page);
10541055
page_cache_release(page);
@@ -1061,7 +1062,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
10611062
req->page_descs[req->num_pages].length = tmp;
10621063
req->num_pages++;
10631064

1064-
iov_iter_advance(ii, tmp);
10651065
count += tmp;
10661066
pos += tmp;
10671067
offset += tmp;

0 commit comments

Comments
 (0)