4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Thomas Gleixner <t...@linutronix.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 <t...@linutronix.de>
Acked-by: Andy Lutomirski <l...@amacapital.net>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Mathias Krause <mini...@googlemail.com>
Link: http://lkml.kernel.org/r/20170410151723.602367...@linutronix.de
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
arch/x86/include/asm/elf.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -278,7 +278,7 @@ struct task_struct;
#define ARCH_DLINFO_IA32
\
do { \
- if (vdso32_enabled) { \
+ if (VDSO_CURRENT_BASE) { \
NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY); \
NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE); \
} \
