Re: [tip: core/urgent] rseq: Reject unknown flags on rseq unregister

[Mathieu Desnoyers]

----- On Dec 25, 2019, at 6:39 AM, Borislav Petkov bp@xxxxxxxxx wrote:

> On Wed, Dec 25, 2019 at 10:38:53AM -0000, tip-bot2 for Mathieu Desnoyers wrote:
>> The following commit has been merged into the core/urgent branch of tip:
>> 
>> Commit-ID:     66528a4575eee9f5a5270219894ab6178f146e84
>> Gitweb:
>> https://git.kernel.org/tip/66528a4575eee9f5a5270219894ab6178f146e84
>> Author:        Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
>> AuthorDate:    Wed, 11 Dec 2019 11:17:11 -05:00
>> Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
>> CommitterDate: Wed, 25 Dec 2019 10:41:20 +01:00
>> 
>> rseq: Reject unknown flags on rseq unregister
>> 
>> It is preferrable to reject unknown flags within rseq unregistration
>> rather than to ignore them. It is an oversight caused by the fact that
>> the check for unknown flags is after the rseq unregister flag check.
>> 
>> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
>> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Link:
>> https://lkml.kernel.org/r/20191211161713.4490-2-mathieu.desnoyers@xxxxxxxxxxxx
>> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
>> ---
>>  kernel/rseq.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/kernel/rseq.c b/kernel/rseq.c
>> index 27c48eb..a4f86a9 100644
>> --- a/kernel/rseq.c
>> +++ b/kernel/rseq.c
>> @@ -310,6 +310,8 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32,
>> rseq_len,
>>  	int ret;
>>  
>>  	if (flags & RSEQ_FLAG_UNREGISTER) {
>> +		if (flags & ~RSEQ_FLAG_UNREGISTER)
>> +			return -EINVAL;
>>  		/* Unregister rseq for current thread. */
>>  		if (current->rseq != rseq || !current->rseq)
>>  			return -EINVAL;
> 
> Cc: stable perhaps?

This could indeed be a candidate for stable, even though it's just a stricter
checking of unknown flags (returning an error rather than ignoring them).

Adding stable in CC here.

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com