In the Linux kernel, the following vulnerability has been resolved:
ext4: fix uninitialized ratelimit_state->lock access in __ext4_fill_super()
In the following concurrency we will access the uninitialized rs->lock:
ext4_fill_super
ext4_register_sysfs
// sysfs registered msg_ratelimit_interval_ms
// Other processes modify rs->interval to
// non-zero via msg_ratelimit_interval_ms
ext4_orphan_cleanup
ext4_msg(sb, KERN_INFO, "Errors on filesystem, "
__ext4_msg
___ratelimit(&(EXT4_SB(sb)->s_msg_ratelimit_state)
if (!rs->interval) // do nothing if interval is 0
return 1;
raw_spin_trylock_irqsave(&rs->lock, flags)
raw_spin_trylock(lock)
_raw_spin_trylock
__raw_spin_trylock
spin_acquire(&lock->dep_map, 0, 1, RET_IP)
lock_acquire
__lock_acquire
register_lock_class
assign_lock_key
dump_stack();
ratelimit_state_init(&sbi->s_msg_ratelimit_state, 5 * HZ, 10);
raw_spin_lock_init(&rs->lock);
// init rs->lock here
and get the following dump_stack:
Normally interval is 0 until s_msg_ratelimit_state is initialized, so
___ratelimit() does nothing. But registering sysfs precedes initializing
rs->lock, so it is possible to change rs->interval to a non-zero value
via the msg_ratelimit_interval_ms interface of sysfs while rs->lock is
uninitialized, and then a call to ext4_msg triggers the problem by
accessing an uninitialized rs->lock. Therefore register sysfs after all
initializations are complete to avoid such problems.