Commit 4f134b89 authored Nov 30, 2020 by Willy Tarreau Committed by Linus Torvalds Dec 03, 2020

lib/syscall: fix syscall registers retrieval on 32-bit platforms



Lilith >_> and Claudio Bozzato of Cisco Talos security team reported
that collect_syscall() improperly casts the syscall registers to 64-bit
values leaking the uninitialized last 24 bytes on 32-bit platforms, that
are visible in /proc/self/syscall.

The cause is that info->data.args are u64 while syscall_get_arguments()
uses longs, as hinted by the bogus pointer cast in the function.

Let's just proceed like the other call places, by retrieving the
registers into an array of longs before assigning them to the caller's
array.  This was successfully tested on x86_64, i386 and ppc32.

Reference: CVE-2020-28588, TALOS-2020-1211
Fixes: 631b7aba ("ptrace: Remove maxargs from task_current_syscall()")
Cc: Greg KH <greg@kroah.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Michael Ellerman <mpe@ellerman.id.au> (ppc32)
Signed-off-by: Willy Tarreau <w@1wt.eu>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 34816d20

lib/syscall.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -7,6 +7,7 @@

		static int collect_syscall(struct task_struct target, struct syscall_info info)
		{
		unsigned long args[6] = { };
		struct pt_regs *regs;

		if (!try_get_task_stack(target)) {
		@@ -27,8 +28,14 @@ static int collect_syscall(struct task_struct target, struct syscall_info info

		info->data.nr = syscall_get_nr(target, regs);
		if (info->data.nr != -1L)
		syscall_get_arguments(target, regs,
		(unsigned long *)&info->data.args[0]);
		syscall_get_arguments(target, regs, args);

		info->data.args[0] = args[0];
		info->data.args[1] = args[1];
		info->data.args[2] = args[2];
		info->data.args[3] = args[3];
		info->data.args[4] = args[4];
		info->data.args[5] = args[5];

		put_task_stack(target);
		return 0;

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