[PATCH] missing ->mmap_sem around find_vma() in swp_emulate.c

[Russell King - ARM Linux]

On Thu, Dec 20, 2012 at 08:15:47AM +0100, Dirk Behme wrote:
> Am 16.12.2012 01:25, schrieb Al Viro:
>> find_vma() is *not* safe when somebody else is removing vmas.  Not just
>> the return value might get bogus just as you are getting it (this instance
>> doesn't try to dereference the resulting vma), the search itself can get
>> buggered in rather spectacular ways.  IOW, ->mmap_sem really, really is
>> not optional here.
>>
>> Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
>> ---
>> diff --git a/arch/arm/kernel/swp_emulate.c b/arch/arm/kernel/swp_emulate.c
>> index df74518..ab1017b 100644
>> --- a/arch/arm/kernel/swp_emulate.c
>> +++ b/arch/arm/kernel/swp_emulate.c
>> @@ -109,10 +109,12 @@ static void set_segfault(struct pt_regs *regs, unsigned long addr)
>>   {
>>   	siginfo_t info;
>>
>> +	down_read(&current->mm->mmap_sem);
>>   	if (find_vma(current->mm, addr) == NULL)
>>   		info.si_code = SEGV_MAPERR;
>>   	else
>>   		info.si_code = SEGV_ACCERR;
>> +	up_read(&current->mm->mmap_sem);
>>
>>   	info.si_signo = SIGSEGV;
>>   	info.si_errno = 0;
>
> Any comment on this?

Any comment required on this?  No, it's from Al Viro, which means it's
(mostly) always correct.  I'll look at merging it soon.