linux-kernel - [PATCH stable 5.10.y] mm/filemap: fix infinite loop in generic_file_buffered

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Date:   Tue, 19 Sep 2023 16:28:15 -0700
From:   Suraj Jitindar Singh <surajjs@...zon.com>
To:     <stable@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <kent.overstreet@...il.com>, <axboe@...nel.dk>,
        <sjitindarsingh@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Suraj Jitindar Singh <surajjs@...zon.com>
Subject: [PATCH stable 5.10.y] mm/filemap: fix infinite loop in generic_file_buffered_read()

From: Kent Overstreet <kent.overstreet@...il.com>

commit 3644e2d2dda78e21edd8f5415b6d7ab03f5f54f3 upstream.

If iter->count is 0 and iocb->ki_pos is page aligned, this causes
nr_pages to be 0.

Then in generic_file_buffered_read_get_pages() find_get_pages_contig()
returns 0 - because we asked for 0 pages, so we call
generic_file_buffered_read_no_cached_page() which attempts to add a page
to the page cache, which fails with -EEXIST, and then we loop. Oops...

Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>
Reported-by: Jens Axboe <axboe@...nel.dk>
Reviewed-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Suraj Jitindar Singh <surajjs@...zon.com>
---
 mm/filemap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index 3a983bc1a71c..3b0d8c6dd587 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2203,6 +2203,9 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
 
 	if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
 		return 0;
+	if (unlikely(!iov_iter_count(iter)))
+		return 0;
+
 	iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
 
 	index = *ppos >> PAGE_SHIFT;
-- 
2.34.1