linux-kernel - [PATCH 3.10 231/268] x86/vdso: Plug race between mapping and ELF header setup

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Message-Id: <1497897167-14556-232-git-send-email-w@1wt.eu>
Date:   Mon, 19 Jun 2017 20:32:10 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Mathias Krause <minipli@...glemail.com>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 231/268] x86/vdso: Plug race between mapping and ELF header setup

From: Thomas Gleixner <tglx@...utronix.de>

commit 6fdc6dd90272ce7e75d744f71535cfbd8d77da81 upstream.

The vsyscall32 sysctl can racy against a concurrent fork when it switches
from disabled to enabled:

    arch_setup_additional_pages()
	if (vdso32_enabled)
           --> No mapping
                                        sysctl.vsysscall32()
                                          --> vdso32_enabled = true
    create_elf_tables()
      ARCH_DLINFO_IA32
        if (vdso32_enabled) {
           --> Add VDSO entry with NULL pointer

Make ARCH_DLINFO_IA32 check whether the VDSO mapping has been set up for
the newly forked process or not.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Andy Lutomirski <luto@...capital.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Mathias Krause <minipli@...glemail.com>
Link: http://lkml.kernel.org/r/20170410151723.602367196@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/x86/include/asm/elf.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 01f15b2..2fa7f4f 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -272,7 +272,7 @@ struct task_struct;
 
 #define	ARCH_DLINFO_IA32(vdso_enabled)					\
 do {									\
-	if (vdso_enabled) {						\
+	if (VDSO_CURRENT_BASE) {					\
 		NEW_AUX_ENT(AT_SYSINFO,	VDSO_ENTRY);			\
 		NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE);	\
 	}								\
-- 
2.8.0.rc2.1.gbe9624a