From: Demi Marie Obenour demi@invisiblethingslab.com
commit b90ecc0379eb7bbe79337b0c7289390a98752646 upstream.
Currently, associating a loop device with a different file descriptor does not increment its diskseq. This allows the following race condition:
1. Program X opens a loop device 2. Program X gets the diskseq of the loop device. 3. Program X associates a file with the loop device. 4. Program X passes the loop device major, minor, and diskseq to something. 5. Program X exits. 6. Program Y detaches the file from the loop device. 7. Program Y attaches a different file to the loop device. 8. The opener finally gets around to opening the loop device and checks that the diskseq is what it expects it to be. Even though the diskseq is the expected value, the result is that the opener is accessing the wrong file.
From discussions with Christoph Hellwig, it appears that
disk_force_media_change() was supposed to call inc_diskseq(), but in fact it does not. Adding a Fixes: tag to indicate this. Christoph's Reported-by is because he stated that disk_force_media_change() calls inc_diskseq(), which is what led me to discover that it should but does not.
Reported-by: Christoph Hellwig hch@infradead.org Signed-off-by: Demi Marie Obenour demi@invisiblethingslab.com Fixes: e6138dc12de9 ("block: add a helper to raise a media changed event") Cc: stable@vger.kernel.org # 5.15+ Reviewed-by: Christoph Hellwig hch@lst.de Link: https://lore.kernel.org/r/20230607170837.1559-1-demi@invisiblethingslab.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- block/disk-events.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/block/disk-events.c b/block/disk-events.c index 8b1b63225738..0cfac464e6d1 100644 --- a/block/disk-events.c +++ b/block/disk-events.c @@ -307,6 +307,7 @@ bool disk_force_media_change(struct gendisk *disk, unsigned int events) if (!(events & DISK_EVENT_MEDIA_CHANGE)) return false;
+ inc_diskseq(disk); if (__invalidate_device(disk->part0, true)) pr_warn("VFS: busy inodes on changed media %s\n", disk->disk_name);