In the Linux kernel, the following vulnerability has been resolved:
f2fs: check discard support for conventional zones
As the helper function f2fsbdevsupportdiscard() shows, f2fs checks if the target block devices support discard by calling bdevmaxdiscardsectors() and bdeviszoned(). This check works well for most cases, but it does not work for conventional zones on zoned block devices. F2fs assumes that zoned block devices support discard, and calls _submitdiscardcmd(). When _submitdiscardcmd() is called for sequential write required zones, it works fine since _submitdiscardcmd() issues zone reset commands instead of discard commands. However, when _submitdiscardcmd() is called for conventional zones, _blkdevissue_discard() is called even when the devices do not support discard.
The inappropriate _blkdevissuediscard() call was not a problem before the commit 30f1e7241422 ("block: move discard checks into the ioctl handler") because _blkdevissuediscard() checked if the target devices support discard or not. If not, it returned EOPNOTSUPP. After the commit, _blkdevissuediscard() no longer checks it. It always returns zero and sets NULL to the given bio pointer. This NULL pointer triggers f2fsbugon() in _submitdiscardcmd(). The BUG is recreated with the commands below at the umount step, where /dev/nullb0 is a zoned null_blk with 5GB total size, 128MB zone size and 10 conventional zones.
$ mkfs.f2fs -f -m /dev/nullb0 $ mount /dev/nullb0 /mnt $ for ((i=0;i<5;i++)); do dd if=/dev/zero of=/mnt/test bs=65536 count=1600 conv=fsync; done $ umount /mnt
To fix the BUG, avoid the inappropriate _blkdevissue_discard() call. When discard is requested for conventional zones, check if the device supports discard or not. If not, return EOPNOTSUPP.