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author | Oleg Nesterov <oleg@redhat.com> | 2010-05-26 17:43:03 -0400 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-05-27 12:12:45 -0400 |
commit | 7d64224217b53b23243fd2aa428001486f2a5da5 (patch) | |
tree | 23219e8d6d81e891fe2571e10be6feab7f81cd49 /scripts | |
parent | 363da4022c2753bf4b4b54a1bb9e4527fdcb9d5d (diff) |
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 'scripts')
0 files changed, 0 insertions, 0 deletions