filemap: Fix bounds checking in filemap_read()

ace149e0 · Trond Myklebust <[email protected]> · 2024-09-13 13:57:04 -04:00

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 <[email protected]>
Fixes: c2a9737f45e2 ("vfs,mm: fix a dead loop in truncate_inode_pages_range()")
Tested-by: Mike Snitzer <[email protected]>
Signed-off-by: Trond Myklebust <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: ace149e0830c380ddfce7e466fe860ca502fe4ee
Parents: a9cda7c0

Changes

1 files changed · +1 −1

File	Status	Add	Del	Content
mm/filemap.c	modified	+1	−1	View file

mm/filemap.c

View file

diff --git a/mm/filemap.c b/mm/filemap.c
index 36d2296..56fa431 100644
--- 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 {