[PATCH] nilfs2: fix general protection fault in nilfs_lookup_dirty_data_buffers()

Ryusuke Konishi
2023-08-05T13:20:48Z

A syzbot stress test reported that create_empty_buffers() called from
nilfs_lookup_dirty_data_buffers() can cause a general protection fault.

Analysis using its reproducer revealed that the back reference "mapping"
from a page/folio has been changed to NULL after dirty page/folio gang
lookup in nilfs_lookup_dirty_data_buffers().

Fix this issue by excluding pages/folios from being collected if, after
acquiring a lock on each page/folio, its back reference "mapping"
differs from the pointer to the address space struct that held the
page/folio.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reported-by: syzbot+0ad741797f4565e7e2d2@syzkaller.appspotmail.com
Closes: https://lkml.kernel.org/r/0000000000002930a705fc32b231@google.com
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>
---
fs/nilfs2/segment.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 581691e4be49..7ec16879756e 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -725,6 +725,11 @@ static size_t nilfs_lookup_dirty_data_buffers(struct inode *inode,
struct folio *folio = fbatch.folios[i];

folio_lock(folio);
+ if (unlikely(folio->mapping != mapping)) {
+ /* Exclude folios removed from the address space */
+ folio_unlock(folio);
+ continue;
+ }
head = folio_buffers(folio);
if (!head) {
create_empty_buffers(&folio->page, i_blocksize(inode), 0);
--
2.34.1