| From | Greg Kroah-Hartman <> | Subject | [PATCH 3.14 50/70] fuse: break infinite loop in fuse_fill_write_pages() | Date | Tue, 23 Feb 2016 19:33:59 -0800 |
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3.14-stable review patch. If anyone has any objections, please let me know.
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From: Roman Gushchin <klamm@yandex-team.ru>
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.
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") Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- fs/fuse/file.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -1006,6 +1006,7 @@ static ssize_t fuse_fill_write_pages(str 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); @@ -1018,7 +1019,6 @@ 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;
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