linux-kernel - siginfo memory leak?

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Date:	Mon, 23 May 2016 13:16:30 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Aleksa Sarai <asarai@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-s390@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: siginfo memory leak?

Hi,
Aleksa has reported that strace tells a bogus si_errno while debugging
something on s390:
[pid 20799] --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_errno=2510266, si_addr=0x100000000000000}

A quick look into do_sigsegv shows that siginfo is not completely
initialized and it indeed might leak the previous stack content
which will later gets to userspace. So unless I am missing something
we need something like the trivial patch below. I have tried to look
around and it seems that this is not the only place...

x86 do_error_trap doesn't do any initialization at all! It is hard to
tell other places. I have checked some and most of them do some
(partial) initialization.

So my primary question is whether we want to fix all those potential
places one by one or come up with something more systematic (e.g. a
macro to declare on stack siginfo). Btw. I am not even sure partial
initializations are correct and memset should be used unconditioanlly
(e.g. fill_sigtrap_info does do that).
---
diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
index 791a4146052c..41913fac14e4 100644
--- a/arch/s390/mm/fault.c
+++ b/arch/s390/mm/fault.c
@@ -248,6 +248,7 @@ static noinline void do_sigsegv(struct pt_regs *regs, int si_code)
 	si.si_signo = SIGSEGV;
 	si.si_code = si_code;
 	si.si_addr = (void __user *)(regs->int_parm_long & __FAIL_ADDR_MASK);
+	si.si_errno = 0;
 	force_sig_info(SIGSEGV, &si, current);
 }
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index ade185a46b1d..f8b66ddbb47d 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -286,6 +286,7 @@ static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
 
 	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) !=
 			NOTIFY_STOP) {
+		memset(&info, 0, sizeof(info));
 		conditional_sti(regs);
 		do_trap(trapnr, signr, str, regs, error_code,
 			fill_trap_info(regs, signr, trapnr, &info));
 
-- 
Michal Hocko
SUSE Labs