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authorAndy Lutomirski <luto@kernel.org>2016-09-15 22:45:47 -0700
committerIngo Molnar <mingo@kernel.org>2016-09-16 09:18:53 +0200
commitaa1f1a639621672b68f654dc815a7d8298ff396f (patch)
treecf72e7859a0fbc24bb11aac984946383f6eb0aba
parent74327a3e884a0ff895ba7b51d3488e6a177407b2 (diff)
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>
-rw-r--r--lib/syscall.c15
1 files 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;
}