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

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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>
This commit is contained in:
Andy Lutomirski 2016-09-15 22:45:47 -07:00 committed by Ingo Molnar
parent 74327a3e88
commit aa1f1a6396
1 changed files with 13 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

15
lib/syscall.c
View file

@ -7,9 +7,19 @@ static int collect_syscall(struct task_struct *target, long *callno,
unsigned long args[6], unsigned int maxargs, unsigned long args[6], unsigned int maxargs,
unsigned long *sp, unsigned long *pc) unsigned long *sp, unsigned long *pc)
{ {
struct pt_regs *regs = task_pt_regs(target); struct pt_regs *regs;
if (unlikely(!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; return -EAGAIN;
}
*sp = user_stack_pointer(regs); *sp = user_stack_pointer(regs);
*pc = instruction_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) if (*callno != -1L && maxargs > 0)
syscall_get_arguments(target, regs, 0, maxargs, args); syscall_get_arguments(target, regs, 0, maxargs, args);
put_task_stack(target);
return 0; return 0;
} }