diff mbox series

filemap: Fix bounds checking in filemap_read()

Message ID c6f35a86fe9ae6aa33b2fd3983b4023c2f4f9c13.1726250071.git.trond.myklebust@hammerspace.com (mailing list archive)
State New
Headers show
Series filemap: Fix bounds checking in filemap_read() | expand

Commit Message

Trond Myklebust Sept. 13, 2024, 5:57 p.m. UTC 
From: Trond Myklebust <trond.myklebust@hammerspace.com>

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>
---
 mm/filemap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Matthew Wilcox Sept. 13, 2024, 6:21 p.m. UTC | #1 
On Fri, Sep 13, 2024 at 01:57:04PM -0400, trondmy@kernel.org wrote:
> 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.

Are we guaranteed that ki_pos lies in the range [0..s_maxbytes)?
I'm not too familiar with the upper paths of the VFS and what guarantees
we can depend on.  If we are guaranteed that, could somebody document
it (and indeed create kernel-doc for struct kiocb)?

>  
> -	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 {
> -- 
> 2.46.0
>
Dave Chinner Sept. 16, 2024, 9:55 p.m. UTC | #2 
On Fri, Sep 13, 2024 at 07:21:54PM +0100, Matthew Wilcox wrote:
> On Fri, Sep 13, 2024 at 01:57:04PM -0400, trondmy@kernel.org wrote:
> > 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.
> 
> Are we guaranteed that ki_pos lies in the range [0..s_maxbytes)?
> I'm not too familiar with the upper paths of the VFS and what guarantees
> we can depend on.  If we are guaranteed that, could somebody document
> it (and indeed create kernel-doc for struct kiocb)?

filemap_read() checks this itself before doing anything else:

	if (unlikely(iocb->ki_pos >= inode->i_sb->s_maxbytes))
                return 0;

i.e. there is no guarantee provided by the upper layers, it's first
checked right here in any buffered read path...

-Dave.
diff mbox series

Patch

diff --git a/mm/filemap.c b/mm/filemap.c
index d62150418b91..c69227ccdabb 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2605,7 +2605,7 @@  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 {