854fbd6e5f
Commit:aa1f1a6396("lib/syscall: Pin the task stack in collect_syscall()") ... added logic to handle a process stack not existing, but left sp and pc uninitialized, which can be later reported via /proc/$pid/syscall for zombie processes, potentially exposing kernel memory to userspace. Zombie /proc/$pid/syscall before: -1 0xffffffff9a060100 0xffff92f42d6ad900 Zombie /proc/$pid/syscall after: -1 0x0 0x0 Reported-by: Robert Święcki <robert@swiecki.net> Signed-off-by: Kees Cook <keescook@chromium.org> Reviewed-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> Cc: stable@vger.kernel.org # v4.9+ Fixes:aa1f1a6396("lib/syscall: Pin the task stack in collect_syscall()") Link: http://lkml.kernel.org/r/20170323224616.GA92694@beast Signed-off-by: Ingo Molnar <mingo@kernel.org>
87 lines
2.6 KiB
C
87 lines
2.6 KiB
C
#include <linux/ptrace.h>
|
|
#include <linux/sched.h>
|
|
#include <linux/sched/task_stack.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. */
|
|
*sp = *pc = 0;
|
|
*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;
|
|
}
|