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authorRoman Gushchin <klamm@yandex-team.ru>2015-10-12 16:33:44 +0300
committerMiklos Szeredi <miklos@szeredi.hu>2015-11-10 10:32:37 +0100
commit3ca8138f014a913f98e6ef40e939868e1e9ea876 (patch)
treef8958826e39c9270e3786f773f9720114177770e /fs/fuse
parent2c5816b4beccc8ba709144539f6fdd764f8fa49c (diff)
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>
Diffstat (limited to 'fs/fuse')
-rw-r--r--fs/fuse/file.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index f523f2f04c19..195476a24148 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1049,6 +1049,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
tmp = iov_iter_copy_from_user_atomic(page, ii, offset, bytes);
flush_dcache_page(page);
+ iov_iter_advance(ii, tmp);
if (!tmp) {
unlock_page(page);
page_cache_release(page);
@@ -1061,7 +1062,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
req->page_descs[req->num_pages].length = tmp;
req->num_pages++;
- iov_iter_advance(ii, tmp);
count += tmp;
pos += tmp;
offset += tmp;