Patch "x86/vdso: Ensure vdso32_enabled gets set to valid values only" has been added to the 4.4-stable tree

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

x86/vdso: Ensure vdso32_enabled gets set to valid values only

to the 4.4-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-ensure-vdso32_enabled-gets-set-to-valid-values-only.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Mathias Krause <[email protected]>
Date: Mon, 10 Apr 2017 17:14:27 +0200
Subject: x86/vdso: Ensure vdso32_enabled gets set to valid values only

From: Mathias Krause <[email protected]>

commit c06989da39cdb10604d572c8c7ea8c8c97f3c483 upstream.

vdso_enabled can be set to arbitrary integer values via the kernel command line 'vdso32=' parameter or via 'sysctl abi.vsyscall32'.

load_vdso32() only maps VDSO if vdso_enabled == 1, but ARCH_DLINFO_IA32 merily checks for vdso_enabled != 0. As a consequence the AT_SYSINFO_EHDR auxiliary vector for the VDSO_ENTRY is emitted with a NULL pointer which causes a segfault when the application tries to use the VDSO.

Restrict the valid arguments on the command line and the sysctl to 0 and 1.

---
 arch/x86/entry/vdso/vdso32-setup.c |   11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

@@ -31,8 +31,10 @@ static int __init vdso32_setup(char *s)
 {
 	vdso32_enabled = simple_strtoul(s, NULL, 0);
 
-	if (vdso32_enabled > 1)
+	if (vdso32_enabled > 1) {
 		pr_warn("vdso32 values other than 0 and 1 are no longer allowed; vdso disabled\n");
+		vdso32_enabled = 0;
+	}
 
 	return 1;
 }

@@ -63,13 +65,18 @@ subsys_initcall(sysenter_setup);
 /* Register vsyscall32 into the ABI table */
 #include <linux/sysctl.h>
 
+static const int zero;
+static const int one = 1;
+
 static struct ctl_table abi_table2[] = {
 	{
 		.procname	= "vsyscall32",
 		.data		= &vdso32_enabled,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= (int *)&zero,
+		.extra2		= (int *)&one,
 	},
 	{}
 };

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

queue-4.4/x86-vdso-ensure-vdso32_enabled-gets-set-to-valid-values-only.patch queue-4.4/x86-vdso-plug-race-between-mapping-and-elf-header-setup.patch