On 07/03/2013 09:54 PM, Oleg Nesterov wrote:
> On 07/03, Denys Vlasenko wrote:
>>
>> @@ -514,7 +514,7 @@ pipe_write(struct kiocb *iocb, const struct iovec *_iov,
>> __pipe_lock(pipe);
>>
>> if (!pipe->readers) {
>> - send_sig(SIGPIPE, current, 0);
>> + send_sig(SIGPIPE, current, 1);
>
> Honestly, I simply have no idea what makes more sense in this case...
I guess I should have explained what prompted me to send this patch.
I am coding up a gdb extension which looks at a process which received
a signal and tries some heuristics on it which sya whether the observed
signal is a crash, and if it is, how likely it to be exploitable.
For example, a SIGSEGV due to smashed stack is more likely to be
a result of exploitable bug than a division by zero.
I want to quickly filter out cases where signal is clearly not a result
of program bug. Say, if program dies from SIGSEGV (or SIGBUS,
or SIGSYS...) which was *sent by the user via kill(2)*,
then it is not a bug in the program.
Naively, it looks like "if (siginfo.si_code <= 0) not_a_bug()"
is what would do that. In particular, si_code == 0 (SI_USER)
is set by kill(2).
But then I discovered that SI_USER is also set by signals
from other sources. SIGPIPE from write(2) is one of them.
This basically makes "si_code == SI_USER" condition non-informative:
userspace can't really draw any useful conclusion from seeing that.
"Maybe it was a kill(2), maybe it was from kernel". Not good.
Note that other similar signals, say, a SIGTTIN received
when backgrounded read(2) attempts to read from a tty,
use SI_KERNEL code. There is no consistency already.
--
vda
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