CVE-2024-56565

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to drop all discards after creating snapshot on lvm device

Piergiorgio reported a bug in bugzilla as below:

------------[ cut here ]------------ WARNING: CPU: 2 PID: 969 at fs/f2fs/segment.c:1330 RIP: 0010:_submitdiscardcmd+0x27d/0x400 [f2fs] Call Trace: _issuediscardcmd+0x1ca/0x350 [f2fs] issuediscardthread+0x191/0x480 [f2fs] kthread+0xcf/0x100 retfromfork+0x31/0x50 retfromfork_asm+0x1a/0x30

w/ below testcase, it can reproduce this bug quickly: - pvcreate /dev/vdb - vgcreate myvg1 /dev/vdb - lvcreate -L 1024m -n mylv1 myvg1 - mount /dev/myvg1/mylv1 /mnt/f2fs - dd if=/dev/zero of=/mnt/f2fs/file bs=1M count=20 - sync - rm /mnt/f2fs/file - sync - lvcreate -L 1024m -s -n mylv1-snapshot /dev/myvg1/mylv1 - umount /mnt/f2fs

The root cause is: it will update discardmaxbytes of mounted lvm device to zero after creating snapshot on this lvm device, then, _submitdiscardcmd() will pass parameter @nrsects w/ zero value to _blkdevissue_discard(), it returns a NULL bio pointer, result in panic.

This patch changes as below for fixing: 1. Let's drop all remained discards in f2fsunfreeze() if snapshot of lvm device is created. 2. Checking discardmaxbytes before submitting discard during _submitdiscardcmd().