From aa1f1a639621672b68f654dc815a7d8298ff396f Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 15 Sep 2016 22:45:47 -0700 Subject: [PATCH] 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 Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/0bfd8e6d4729c97745d3781a29610a33d0a8091d.1474003868.git.luto@kernel.org Signed-off-by: Ingo Molnar --- lib/syscall.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/lib/syscall.c b/lib/syscall.c index e30e03932480..63239e097b13 100644 --- a/lib/syscall.c +++ b/lib/syscall.c @@ -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; } -- 2.20.1