linux/lib/syscall.c
Andy Lutomirski aa1f1a6396 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>
2016-09-16 09:18:53 +02:00

86 lines
2.6 KiB
C

#include <linux/ptrace.h>
#include <linux/sched.h>
#include <linux/export.h>
#include <asm/syscall.h>
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;
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);
*callno = syscall_get_nr(target, regs);
if (*callno != -1L && maxargs > 0)
syscall_get_arguments(target, regs, 0, maxargs, args);
put_task_stack(target);
return 0;
}
/**
* task_current_syscall - Discover what a blocked task is doing.
* @target: thread to examine
* @callno: filled with system call number or -1
* @args: filled with @maxargs system call arguments
* @maxargs: number of elements in @args to fill
* @sp: filled with user stack pointer
* @pc: filled with user PC
*
* If @target is blocked in a system call, returns zero with *@callno
* set to the the call's number and @args filled in with its arguments.
* Registers not used for system call arguments may not be available and
* it is not kosher to use &struct user_regset calls while the system
* call is still in progress. Note we may get this result if @target
* has finished its system call but not yet returned to user mode, such
* as when it's stopped for signal handling or syscall exit tracing.
*
* If @target is blocked in the kernel during a fault or exception,
* returns zero with *@callno set to -1 and does not fill in @args.
* If so, it's now safe to examine @target using &struct user_regset
* get() calls as long as we're sure @target won't return to user mode.
*
* Returns -%EAGAIN if @target does not remain blocked.
*
* Returns -%EINVAL if @maxargs is too large (maximum is six).
*/
int task_current_syscall(struct task_struct *target, long *callno,
unsigned long args[6], unsigned int maxargs,
unsigned long *sp, unsigned long *pc)
{
long state;
unsigned long ncsw;
if (unlikely(maxargs > 6))
return -EINVAL;
if (target == current)
return collect_syscall(target, callno, args, maxargs, sp, pc);
state = target->state;
if (unlikely(!state))
return -EAGAIN;
ncsw = wait_task_inactive(target, state);
if (unlikely(!ncsw) ||
unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
unlikely(wait_task_inactive(target, state) != ncsw))
return -EAGAIN;
return 0;
}