From edea0d03ee5f0ae0051b6adb6681ebdf976b1ca4 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Sun, 20 Jan 2013 20:25:47 +0100 Subject: ia64: kill thread_matches(), unexport ptrace_check_attach() The ia64 function "thread_matches()" has no users since commit e868a55c2a8c ("[IA64] remove find_thread_for_addr()"). Remove it. This allows us to make ptrace_check_attach() static to kernel/ptrace.c, which is good since we'll need to change the semantics of it and fix up all the callers. Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds --- kernel/ptrace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/ptrace.c') diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 1599157336a6..612a56126851 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -139,7 +139,7 @@ void __ptrace_unlink(struct task_struct *child) * RETURNS: * 0 on success, -ESRCH if %child is not ready. */ -int ptrace_check_attach(struct task_struct *child, bool ignore_state) +static int ptrace_check_attach(struct task_struct *child, bool ignore_state) { int ret = -ESRCH; -- cgit v1.2.3 From 910ffdb18a6408e14febbb6e4b6840fd2c928c82 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 21 Jan 2013 20:47:41 +0100 Subject: ptrace: introduce signal_wake_up_state() and ptrace_signal_wake_up() Cleanup and preparation for the next change. signal_wake_up(resume => true) is overused. None of ptrace/jctl callers actually want to wakeup a TASK_WAKEKILL task, but they can't specify the necessary mask. Turn signal_wake_up() into signal_wake_up_state(state), reintroduce signal_wake_up() as a trivial helper, and add ptrace_signal_wake_up() which adds __TASK_TRACED. This way ptrace_signal_wake_up() can work "inside" ptrace_request() even if the tracee doesn't have the TASK_WAKEKILL bit set. Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds --- kernel/ptrace.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'kernel/ptrace.c') diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 612a56126851..62f7c2774b16 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -117,7 +117,7 @@ void __ptrace_unlink(struct task_struct *child) * TASK_KILLABLE sleeps. */ if (child->jobctl & JOBCTL_STOP_PENDING || task_is_traced(child)) - signal_wake_up(child, task_is_traced(child)); + ptrace_signal_wake_up(child, true); spin_unlock(&child->sighand->siglock); } @@ -317,7 +317,7 @@ static int ptrace_attach(struct task_struct *task, long request, */ if (task_is_stopped(task) && task_set_jobctl_pending(task, JOBCTL_TRAP_STOP | JOBCTL_TRAPPING)) - signal_wake_up(task, 1); + signal_wake_up_state(task, __TASK_STOPPED); spin_unlock(&task->sighand->siglock); @@ -737,7 +737,7 @@ int ptrace_request(struct task_struct *child, long request, * tracee into STOP. */ if (likely(task_set_jobctl_pending(child, JOBCTL_TRAP_STOP))) - signal_wake_up(child, child->jobctl & JOBCTL_LISTENING); + ptrace_signal_wake_up(child, child->jobctl & JOBCTL_LISTENING); unlock_task_sighand(child, &flags); ret = 0; @@ -763,7 +763,7 @@ int ptrace_request(struct task_struct *child, long request, * start of this trap and now. Trigger re-trap. */ if (child->jobctl & JOBCTL_TRAP_NOTIFY) - signal_wake_up(child, true); + ptrace_signal_wake_up(child, true); ret = 0; } unlock_task_sighand(child, &flags); -- cgit v1.2.3 From 9899d11f654474d2d54ea52ceaa2a1f4db3abd68 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 21 Jan 2013 20:48:00 +0100 Subject: ptrace: ensure arch_ptrace/ptrace_request can never race with SIGKILL putreg() assumes that the tracee is not running and pt_regs_access() can safely play with its stack. However a killed tracee can return from ptrace_stop() to the low-level asm code and do RESTORE_REST, this means that debugger can actually read/modify the kernel stack until the tracee does SAVE_REST again. set_task_blockstep() can race with SIGKILL too and in some sense this race is even worse, the very fact the tracee can be woken up breaks the logic. As Linus suggested we can clear TASK_WAKEKILL around the arch_ptrace() call, this ensures that nobody can ever wakeup the tracee while the debugger looks at it. Not only this fixes the mentioned problems, we can do some cleanups/simplifications in arch_ptrace() paths. Probably ptrace_unfreeze_traced() needs more callers, for example it makes sense to make the tracee killable for oom-killer before access_process_vm(). While at it, add the comment into may_ptrace_stop() to explain why ptrace_stop() still can't rely on SIGKILL and signal_pending_state(). Reported-by: Salman Qazi Reported-by: Suleiman Souhlal Suggested-by: Linus Torvalds Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds --- kernel/ptrace.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 54 insertions(+), 10 deletions(-) (limited to 'kernel/ptrace.c') diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 62f7c2774b16..6cbeaae4406d 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -122,6 +122,40 @@ void __ptrace_unlink(struct task_struct *child) spin_unlock(&child->sighand->siglock); } +/* Ensure that nothing can wake it up, even SIGKILL */ +static bool ptrace_freeze_traced(struct task_struct *task) +{ + bool ret = false; + + /* Lockless, nobody but us can set this flag */ + if (task->jobctl & JOBCTL_LISTENING) + return ret; + + spin_lock_irq(&task->sighand->siglock); + if (task_is_traced(task) && !__fatal_signal_pending(task)) { + task->state = __TASK_TRACED; + ret = true; + } + spin_unlock_irq(&task->sighand->siglock); + + return ret; +} + +static void ptrace_unfreeze_traced(struct task_struct *task) +{ + if (task->state != __TASK_TRACED) + return; + + WARN_ON(!task->ptrace || task->parent != current); + + spin_lock_irq(&task->sighand->siglock); + if (__fatal_signal_pending(task)) + wake_up_state(task, __TASK_TRACED); + else + task->state = TASK_TRACED; + spin_unlock_irq(&task->sighand->siglock); +} + /** * ptrace_check_attach - check whether ptracee is ready for ptrace operation * @child: ptracee to check for @@ -151,24 +185,29 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state) * be changed by us so it's not changing right after this. */ read_lock(&tasklist_lock); - if ((child->ptrace & PT_PTRACED) && child->parent == current) { + if (child->ptrace && child->parent == current) { + WARN_ON(child->state == __TASK_TRACED); /* * child->sighand can't be NULL, release_task() * does ptrace_unlink() before __exit_signal(). */ - spin_lock_irq(&child->sighand->siglock); - WARN_ON_ONCE(task_is_stopped(child)); - if (ignore_state || (task_is_traced(child) && - !(child->jobctl & JOBCTL_LISTENING))) + if (ignore_state || ptrace_freeze_traced(child)) ret = 0; - spin_unlock_irq(&child->sighand->siglock); } read_unlock(&tasklist_lock); - if (!ret && !ignore_state) - ret = wait_task_inactive(child, TASK_TRACED) ? 0 : -ESRCH; + if (!ret && !ignore_state) { + if (!wait_task_inactive(child, __TASK_TRACED)) { + /* + * This can only happen if may_ptrace_stop() fails and + * ptrace_stop() changes ->state back to TASK_RUNNING, + * so we should not worry about leaking __TASK_TRACED. + */ + WARN_ON(child->state == __TASK_TRACED); + ret = -ESRCH; + } + } - /* All systems go.. */ return ret; } @@ -900,6 +939,8 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr, goto out_put_task_struct; ret = arch_ptrace(child, request, addr, data); + if (ret || request != PTRACE_DETACH) + ptrace_unfreeze_traced(child); out_put_task_struct: put_task_struct(child); @@ -1039,8 +1080,11 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid, ret = ptrace_check_attach(child, request == PTRACE_KILL || request == PTRACE_INTERRUPT); - if (!ret) + if (!ret) { ret = compat_arch_ptrace(child, request, addr, data); + if (ret || request != PTRACE_DETACH) + ptrace_unfreeze_traced(child); + } out_put_task_struct: put_task_struct(child); -- cgit v1.2.3