filemap: Fix bounds checking in filemap_read()

[ Upstream commit ace149e0830c380ddfce7e466fe860ca502fe4ee ]

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>
(cherry picked from commit ace149e0830c380ddfce7e466fe860ca502fe4ee)
[Harshit: Minor conflict resolved due to missing commit: 25d6a23e8d28
("filemap: Convert filemap_get_read_batch() to use a folio_batch") in
5.15.y]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index c71e86c12418ea39139ef6b24c1f96cafedf3d45..cc86c5a127b9cc3a7259c63cd1520758b8f6f4d7 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2617,7 +2617,7 @@ 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);
        pagevec_init(&pvec);
 
        do {