From 5b47d59af68a8735e4637bacedcb4baf6f47c73f Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 8 May 2017 13:54:47 -0400 Subject: [PATCH] fix braino in generic_file_read_iter() Wrong sign of iov_iter_revert() argument. Unfortunately, slipped through the testing, since most of the time we don't do anything to the iterator afterwards and potential oops on walking the iter->iov too far backwards is too infrequent to be easily triggered. Add a sanity check in iov_iter_revert() to catch bugs like this one; fortunately, the same braino hadn't happened in other callers, but we'd better have a warning if such thing crops up. Signed-off-by: Al Viro --- lib/iov_iter.c | 2 ++ mm/filemap.c | 2 +- 2 files changed, 3 insertions(+), 1 deletion(-) diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 60abc44385b7..fc9fb29d00eb 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -790,6 +790,8 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll) { if (!unroll) return; + if (WARN_ON(unroll > MAX_RW_COUNT)) + return; i->count += unroll; if (unlikely(i->type & ITER_PIPE)) { struct pipe_inode_info *pipe = i->pipe; diff --git a/mm/filemap.c b/mm/filemap.c index cc480c07c71b..d6e67be1802e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2048,7 +2048,7 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) iocb->ki_pos += retval; count -= retval; } - iov_iter_revert(iter, iov_iter_count(iter) - count); + iov_iter_revert(iter, count - iov_iter_count(iter)); /* * Btrfs can have a short DIO read if we encounter -- 2.20.1