Commit aa1f1a63 authored Sep 15, 2016 by Andy Lutomirski Committed by Ingo Molnar Sep 16, 2016

lib/syscall: Pin the task stack in collect_syscall()

This will avoid a potential read-after-free if collect_syscall()
(e.g. /proc/PID/syscall) is called on an exiting task.

Reported-by: Jann Horn <jann@thejh.net>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/0bfd8e6d4729c97745d3781a29610a33d0a8091d.1474003868.git.luto@kernel.org

Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 74327a3e

lib/syscall.c

+13 −2

Original line number	Diff line number	Diff line
		@@ -7,9 +7,19 @@ static int collect_syscall(struct task_struct target, long callno,
		unsigned long args[6], unsigned int maxargs,
		unsigned long sp, unsigned long pc)
		{
		struct pt_regs *regs = task_pt_regs(target);
		if (unlikely(!regs))
		struct pt_regs *regs;

		if (!try_get_task_stack(target)) {
		/* Task has no stack, so the task isn't in a syscall. */
		*callno = -1;
		return 0;
		}

		regs = task_pt_regs(target);
		if (unlikely(!regs)) {
		put_task_stack(target);
		return -EAGAIN;
		}

		*sp = user_stack_pointer(regs);
		*pc = instruction_pointer(regs);
		@@ -18,6 +28,7 @@ static int collect_syscall(struct task_struct target, long callno,
		if (*callno != -1L && maxargs > 0)
		syscall_get_arguments(target, regs, 0, maxargs, args);

		put_task_stack(target);
		return 0;
		}