On Thu, Dec 3, 2015 at 3:48 PM, Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>>
>> No, I don't. But pr_debug always computes its arguments. See no_printk
>> in printk.h. So this use-after-free happens for all users.
>
> Hmm.
>
> pr_debug() should be a nop unless either DEBUG or CONFIG_DYNAMIC_DEBUG are set
>
> On our production kernels, pr_debug() is a nop.
>
> Can you double check ? Thanks !
Why should it be nop? no_printk thing in printk.h pretty much
explicitly makes it not a nop...
Double-checked: debug_post_sfx leads to some generated code:
debug_post_sfx();
ffffffff8229f256: 48 8b 85 58 fe ff ff mov -0x1a8(%rbp),%rax
ffffffff8229f25d: 48 85 c0 test %rax,%rax
ffffffff8229f260: 74 24 je
ffffffff8229f286 <sctp_do_sm+0x176>
ffffffff8229f262: 8b b0 a8 00 00 00 mov 0xa8(%rax),%esi
ffffffff8229f268: 48 8b 85 60 fe ff ff mov -0x1a0(%rbp),%rax
ffffffff8229f26f: 44 89 85 74 fe ff ff mov %r8d,-0x18c(%rbp)
ffffffff8229f276: 48 8b 78 20 mov 0x20(%rax),%rdi
ffffffff8229f27a: e8 71 28 01 00 callq
ffffffff822b1af0 <sctp_id2assoc>
ffffffff8229f27f: 44 8b 85 74 fe ff ff mov -0x18c(%rbp),%r8d
return error;
}
ffffffff8229f286: 48 81 c4 a0 01 00 00 add $0x1a0,%rsp
ffffffff8229f28d: 44 89 c0 mov %r8d,%eax
ffffffff8229f290: 5b pop %rbx
ffffffff8229f291: 41 5c pop %r12
ffffffff8229f293: 41 5d pop %r13
ffffffff8229f295: 41 5e pop %r14
ffffffff8229f297: 41 5f pop %r15
ffffffff8229f299: 5d pop %rbp
ffffffff8229f29a: c3 retq
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