From 993aae88f8995b3597fac88e3f991d22f5f95143 Mon Sep 17 00:00:00 2001 From: Roman Gushchin Date: Mon, 12 Oct 2015 16:33:44 +0300 Subject: 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 Cc: Maxim Patlasov Cc: Konstantin Khlebnikov Signed-off-by: Roman Gushchin Signed-off-by: Miklos Szeredi Fixes: ea9b9907b82a ("fuse: implement perform_write") Cc: Conflicts: fs/fuse/file.c Change-Id: Id37193373294dd43191469389cfe68ca1736a54b --- fs/fuse/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/fuse/file.c b/fs/fuse/file.c index e5c0b5d..c404e6f 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -932,6 +932,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req, pagefault_enable(); flush_dcache_page(page); + iov_iter_advance(ii, tmp); if (!tmp) { unlock_page(page); page_cache_release(page); @@ -943,7 +944,6 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req, req->pages[req->num_pages] = page; req->num_pages++; - iov_iter_advance(ii, tmp); count += tmp; pos += tmp; offset += tmp; -- cgit v1.1