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author | Oleg Nesterov <oleg@redhat.com> | 2010-05-26 23:43:03 +0200 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-05-27 18:12:45 +0200 |
commit | 7d64224217b53b23243fd2aa428001486f2a5da5 (patch) | |
tree | 23219e8d6d81e891fe2571e10be6feab7f81cd49 /kernel/kmod.c | |
parent | call_usermodehelper: no need to unblock signals (diff) | |
download | linux-7d64224217b53b23243fd2aa428001486f2a5da5.tar.xz linux-7d64224217b53b23243fd2aa428001486f2a5da5.zip |
wait_for_helper: SIGCHLD from user-space can lead to use-after-free
1. wait_for_helper() calls allow_signal(SIGCHLD) to ensure the child
can't autoreap itself.
However, this means that a spurious SIGCHILD from user-space can
set TIF_SIGPENDING and:
- kernel_thread() or sys_wait4() can fail due to signal_pending()
- worse, wait4() can fail before ____call_usermodehelper() execs
or exits. In this case the caller may kfree(subprocess_info)
while the child still uses this memory.
Change the code to use SIG_DFL instead of magic "(void __user *)2"
set by allow_signal(). This means that SIGCHLD won't be delivered,
yet the child won't autoreap itsefl.
The problem is minor, only root can send a signal to this kthread.
2. If sys_wait4(&ret) fails it doesn't populate "ret", in this case
wait_for_helper() reports a random value from uninitialized var.
With this patch sys_wait4() should never fail, but still it makes
sense to initialize ret = -ECHILD so that the caller can notice
the problem.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/kmod.c')
-rw-r--r-- | kernel/kmod.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/kmod.c b/kernel/kmod.c index 7efba6f8e3ec..48daed4c51ba 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -175,16 +175,16 @@ static int wait_for_helper(void *data) struct subprocess_info *sub_info = data; pid_t pid; - /* Install a handler: if SIGCLD isn't handled sys_wait4 won't - * populate the status, but will return -ECHILD. */ - allow_signal(SIGCHLD); + /* If SIGCLD is ignored sys_wait4 won't populate the status. */ + spin_lock_irq(¤t->sighand->siglock); + current->sighand->action[SIGCHLD-1].sa.sa_handler = SIG_DFL; + spin_unlock_irq(¤t->sighand->siglock); pid = kernel_thread(____call_usermodehelper, sub_info, SIGCHLD); if (pid < 0) { sub_info->retval = pid; } else { - int ret; - + int ret = -ECHILD; /* * Normally it is bogus to call wait4() from in-kernel because * wait4() wants to write the exit code to a userspace address. |