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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>
88 lines
2.6 KiB
C
88 lines
2.6 KiB
C
#include <linux/ptrace.h>
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#include <linux/sched.h>
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#include <linux/sched/task_stack.h>
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#include <linux/export.h>
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#include <asm/syscall.h>
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static int collect_syscall(struct task_struct *target, long *callno,
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unsigned long args[6], unsigned int maxargs,
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unsigned long *sp, unsigned long *pc)
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{
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struct pt_regs *regs;
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if (!try_get_task_stack(target)) {
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/* Task has no stack, so the task isn't in a syscall. */
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*sp = *pc = 0;
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*callno = -1;
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return 0;
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}
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regs = task_pt_regs(target);
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if (unlikely(!regs)) {
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put_task_stack(target);
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return -EAGAIN;
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}
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*sp = user_stack_pointer(regs);
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*pc = instruction_pointer(regs);
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*callno = syscall_get_nr(target, regs);
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if (*callno != -1L && maxargs > 0)
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syscall_get_arguments(target, regs, 0, maxargs, args);
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put_task_stack(target);
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return 0;
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}
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/**
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* task_current_syscall - Discover what a blocked task is doing.
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* @target: thread to examine
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* @callno: filled with system call number or -1
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* @args: filled with @maxargs system call arguments
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* @maxargs: number of elements in @args to fill
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* @sp: filled with user stack pointer
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* @pc: filled with user PC
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*
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* If @target is blocked in a system call, returns zero with *@callno
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* set to the the call's number and @args filled in with its arguments.
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* Registers not used for system call arguments may not be available and
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* it is not kosher to use &struct user_regset calls while the system
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* call is still in progress. Note we may get this result if @target
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* has finished its system call but not yet returned to user mode, such
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* as when it's stopped for signal handling or syscall exit tracing.
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*
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* If @target is blocked in the kernel during a fault or exception,
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* returns zero with *@callno set to -1 and does not fill in @args.
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* If so, it's now safe to examine @target using &struct user_regset
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* get() calls as long as we're sure @target won't return to user mode.
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*
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* Returns -%EAGAIN if @target does not remain blocked.
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*
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* Returns -%EINVAL if @maxargs is too large (maximum is six).
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*/
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int task_current_syscall(struct task_struct *target, long *callno,
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unsigned long args[6], unsigned int maxargs,
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unsigned long *sp, unsigned long *pc)
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{
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long state;
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unsigned long ncsw;
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if (unlikely(maxargs > 6))
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return -EINVAL;
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if (target == current)
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return collect_syscall(target, callno, args, maxargs, sp, pc);
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state = target->state;
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if (unlikely(!state))
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return -EAGAIN;
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ncsw = wait_task_inactive(target, state);
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if (unlikely(!ncsw) ||
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unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
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unlikely(wait_task_inactive(target, state) != ncsw))
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return -EAGAIN;
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return 0;
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}
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