Commit a811dc61 authored Jan 12, 2019 by Tycho Andersen Committed by James Morris Jan 15, 2019

seccomp: fix UAF in user-trap code

On the failure path, we do an fput() of the listener fd if the filter fails
to install (e.g. because of a TSYNC race that's lost, or if the thread is
killed, etc.). fput() doesn't actually release the fd, it just ads it to a
work queue. Then the thread proceeds to free the filter, even though the
listener struct file has a reference to it.

To fix this, on the failure path let's set the private data to null, so we
know in ->release() to ignore the filter.

Reported-by: <syzbot+981c26489b2d1c6316ba@syzkaller.appspotmail.com>
Fixes: 6a21cc50 ("seccomp: add a return code to trap to userspace")
Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.morris@microsoft.com>

parent 7939f8be

kernel/seccomp.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -976,6 +976,9 @@ static int seccomp_notify_release(struct inode inode, struct file file)
		struct seccomp_filter *filter = file->private_data;
		struct seccomp_knotif *knotif;

		if (!filter)
		return 0;

		mutex_lock(&filter->notify_lock);

		/*
		@@ -1300,6 +1303,7 @@ out:
		out_put_fd:
		if (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) {
		if (ret < 0) {
		listener_f->private_data = NULL;
		fput(listener_f);
		put_unused_fd(listener);
		} else {

Admin message