diff options
author | Oleg Nesterov <oleg@redhat.com> | 2015-04-16 12:47:29 -0700 |
---|---|---|
committer | Willy Tarreau <w@1wt.eu> | 2015-09-18 13:51:59 +0200 |
commit | f97672b998cec03dceb5a326ab671f120253554e (patch) | |
tree | 864aa9cb9c4ef3a205d41578b68e6d186f80dc3a /kernel | |
parent | 804be11691680c2816f2978189ced2782e99935a (diff) |
ptrace: fix race between ptrace_resume() and wait_task_stopped()
commit b72c186999e689cb0b055ab1c7b3cd8fffbeb5ed upstream.
ptrace_resume() is called when the tracee is still __TASK_TRACED. We set
tracee->exit_code and then wake_up_state() changes tracee->state. If the
tracer's sub-thread does wait() in between, task_stopped_code(ptrace => T)
wrongly looks like another report from tracee.
This confuses debugger, and since wait_task_stopped() clears ->exit_code
the tracee can miss a signal.
Test-case:
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/ptrace.h>
#include <pthread.h>
#include <assert.h>
int pid;
void *waiter(void *arg)
{
int stat;
for (;;) {
assert(pid == wait(&stat));
assert(WIFSTOPPED(stat));
if (WSTOPSIG(stat) == SIGHUP)
continue;
assert(WSTOPSIG(stat) == SIGCONT);
printf("ERR! extra/wrong report:%x\n", stat);
}
}
int main(void)
{
pthread_t thread;
pid = fork();
if (!pid) {
assert(ptrace(PTRACE_TRACEME, 0,0,0) == 0);
for (;;)
kill(getpid(), SIGHUP);
}
assert(pthread_create(&thread, NULL, waiter, NULL) == 0);
for (;;)
ptrace(PTRACE_CONT, pid, 0, SIGCONT);
return 0;
}
Note for stable: the bug is very old, but without 9899d11f6544 "ptrace:
ensure arch_ptrace/ptrace_request can never race with SIGKILL" the fix
should use lock_task_sighand(child).
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Pavel Labath <labath@google.com>
Tested-by: Pavel Labath <labath@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit e3f81ba2f0546f030fc234f7aade3016532c75b1)
Signed-off-by: Willy Tarreau <w@1wt.eu>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/ptrace.c | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 4185220acbef..03da336f13cd 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -516,6 +516,8 @@ static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info) static int ptrace_resume(struct task_struct *child, long request, long data) { + bool need_siglock; + if (!valid_signal(data)) return -EIO; @@ -543,8 +545,26 @@ static int ptrace_resume(struct task_struct *child, long request, long data) user_disable_single_step(child); } + /* + * Change ->exit_code and ->state under siglock to avoid the race + * with wait_task_stopped() in between; a non-zero ->exit_code will + * wrongly look like another report from tracee. + * + * Note that we need siglock even if ->exit_code == data and/or this + * status was not reported yet, the new status must not be cleared by + * wait_task_stopped() after resume. + * + * If data == 0 we do not care if wait_task_stopped() reports the old + * status and clears the code too; this can't race with the tracee, it + * takes siglock after resume. + */ + need_siglock = data && !thread_group_empty(current); + if (need_siglock) + spin_lock_irq(&child->sighand->siglock); child->exit_code = data; wake_up_state(child, __TASK_TRACED); + if (need_siglock) + spin_unlock_irq(&child->sighand->siglock); return 0; } |