Patch "x86/vdso: Plug race between mapping and ELF header setup" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-vdso-plug-race-between-mapping-and-elf-header-setup.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Thomas Gleixner <[email protected]>
Date: Mon, 10 Apr 2017 17:14:28 +0200
Subject: x86/vdso: Plug race between mapping and ELF header setup

From: Thomas Gleixner <[email protected]>

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.

---
 arch/x86/include/asm/elf.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -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);	\
 	}								\

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-efi-don-t-try-to-reserve-runtime-regions.patch queue-4.9/x86-signals-fix-lower-upper-bound-reporting-in-compat-siginfo.patch queue-4.9/x86-vdso-ensure-vdso32_enabled-gets-set-to-valid-values-only.patch queue-4.9/x86-pmem-fix-broken-__copy_user_nocache-cache-bypass-assumptions.patch queue-4.9/x86-vdso-plug-race-between-mapping-and-elf-header-setup.patch queue-4.9/cgroup-kthread-close-race-window-where-new-kthreads-can-be-migrated-to-non-root-cgroups.patch queue-4.9/perf-x86-avoid-exposing-wrong-stale-data-in-intel_pmu_lbr_read_32.patch