filemap: Fix bounds checking in filemap_read()

If the caller supplies an iocb->ki_pos value that is close to the
filesystem upper limit, and an iterator with a count that causes us to
overflow that limit, then filemap_read() enters an infinite loop.

This behaviour was discovered when testing xfstests generic/525 with the
"localio" optimisation for loopback NFS mounts.

Reported-by: Mike Snitzer <snitzer@kernel.org>
Fixes: c2a9737f45e2 ("vfs,mm: fix a dead loop in truncate_inode_pages_range()")
Tested-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 36d22968be9a1e10da42927dd627d3f22c3a747b..56fa431c52af7bba33ad270c0f780bd58100792c 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2625,7 +2625,7 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter,
        if (unlikely(!iov_iter_count(iter)))
                return 0;
 
-       iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
+       iov_iter_truncate(iter, inode->i_sb->s_maxbytes - iocb->ki_pos);
        folio_batch_init(&fbatch);
 
        do {