In the Linux kernel, the following vulnerability has been resolved: md: init bioset in mddevinit IO operations may be needed before mdrun(), such as updating metadata after writing sysfs. Without bioset, this triggers a NULL pointer dereference as below: BUG: kernel NULL pointer dereference, address: 0000000000000020 Call Trace: mdupdatesb+0x658/0xe00 newlevelstore+0xc5/0x120 mdattrstore+0xc9/0x1e0 sysfskfwrite+0x6f/0xa0 kernfsfopwriteiter+0x141/0x2a0 vfswrite+0x1fc/0x5a0 ksys_write+0x79/0x180 _x64syswrite+0x1d/0x30 x64syscall+0x2818/0x2880 dosyscall64+0xa9/0x580 entrySYSCALL64afterhwframe+0x4b/0x53 Reproducer mdadm -CR /dev/md0 -l1 -n2 /dev/sd[cd] echo inactive > /sys/block/md0/md/array_state echo 10 > /sys/block/md0/md/new_level mddevinit() can only be called once per mddev, no need to test if bioset has been initialized anymore.