From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 10 Apr 2017 15:14:28 +0000 (+0200)
Subject: x86/vdso: Plug race between mapping and ELF header setup
X-Git-Tag: v3.12.74~61
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3ebb1b606820857986b4310e5012f78352478774;p=thirdparty%2Fkernel%2Fstable.git

x86/vdso: Plug race between mapping and ELF header setup

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@linutronix.de>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mathias Krause <minipli@googlemail.com>
Link: http://lkml.kernel.org/r/20170410151723.602367196@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 01f15b227d7ed..2fa7f4f6ecb31 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);	\
 	}								\