On Tue, Nov 7, 2017 at 11:43 PM, Vlastimil Babka <vba...@suse.cz> wrote:
> On 11/07/2017 10:38 PM, Kees Cook wrote:
>> The mutex in sysctl_vm_numa_stat_handler() needs to be a global static, not
>> a stack variable, otherwise it doesn't serve any purpose. Also, reading the
>> file with CONFIG_LOCKDEP=y will complain:
>
> Oops, good catch.
>
>> [ 63.258593] INFO: trying to register non-static key.
>> [ 63.259113] the code is fine but needs lockdep annotation.
>> [ 63.259596] turning off the locking correctness validator.
>> [ 63.260073] CPU: 1 PID: 4102 Comm: perl Not tainted
>> 4.14.0-rc8-next-20171107+ #419
>> [ 63.260769] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> Ubuntu-1.8.2-1ubuntu1 04/01/2014
>> [ 63.261570] Call Trace:
>> [ 63.261783] dump_stack+0x5f/0x86
>> [ 63.262062] register_lock_class+0xe4/0x550
>> [ 63.262408] ? __lock_acquire+0x308/0x1170
>> [ 63.262746] __lock_acquire+0x7e/0x1170
>> [ 63.263063] lock_acquire+0x9d/0x1d0
>> [ 63.263363] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
>> [ 63.263777] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
>> [ 63.264192] __mutex_lock+0xb8/0x9a0
>> [ 63.264488] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
>> [ 63.264942] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
>> [ 63.265398] ? sysctl_vm_numa_stat_handler+0x8f/0x2d0
>> [ 63.265840] sysctl_vm_numa_stat_handler+0x8f/0x2d0
>> [ 63.266270] proc_sys_call_handler+0xe3/0x100
>> [ 63.266655] __vfs_read+0x33/0x1b0
>> [ 63.266957] vfs_read+0xa6/0x150
>> [ 63.267244] SyS_read+0x55/0xc0
>> [ 63.267525] do_syscall_64+0x56/0x140
>> [ 63.267850] entry_SYSCALL64_slow_path+0x25/0x25
>>
>> Fixes: 920d5f77d1a25 ("mm, sysctl: make NUMA stats configurable")
>
> Note that this hash is specific to particular next-$DATE as mmotm is
> reimported each day.
Ah yes, duh. :)
>
>> Cc: Jesper Dangaard Brouer <bro...@redhat.com>
>> Cc: Dave Hansen <dave.han...@intel.com>
>> Cc: Ying Huang <ying.hu...@intel.com>
>> Cc: Vlastimil Babka <vba...@suse.cz>
>> Cc: Michal Hocko <mho...@suse.com>
>> Signed-off-by: Kees Cook <keesc...@chromium.org>
>> ---
>> mm/vmstat.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/vmstat.c b/mm/vmstat.c
>> index e0593434fd58..40b2db6db6b1 100644
>> --- a/mm/vmstat.c
>> +++ b/mm/vmstat.c
>> @@ -72,11 +72,12 @@ static void invalid_numa_statistics(void)
>> zero_global_numa_counters();
>> }
>>
>> +static DEFINE_MUTEX(vm_numa_stat_lock);
>> +
>> int sysctl_vm_numa_stat_handler(struct ctl_table *table, int write,
>> void __user *buffer, size_t *length, loff_t *ppos)
>> {
>> int ret, oldval;
>> - DEFINE_MUTEX(vm_numa_stat_lock);
>
> Yeah it was Michal who suggested scoping the mutex here instead of
> global scope, but I think he didn't mean to remove the 'static'
> qualifier, and we both missed that in the review :(
> So the scope under sysctl_vm_numa_stat_handler() should be okay, just
> with the 'static' added.
That part is a matter of taste, I guess. :) But yes, static is important.
-Kees
--
Kees Cook
Pixel Security
