From a811dc61559e0c8003f1086c2a4dc8e4d5ae4cb8 Mon Sep 17 00:00:00 2001 From: Tycho Andersen Date: Sat, 12 Jan 2019 11:24:20 -0700 Subject: [PATCH] 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: 6a21cc50f0c7 ("seccomp: add a return code to trap to userspace") Signed-off-by: Tycho Andersen Acked-by: Kees Cook Signed-off-by: James Morris --- kernel/seccomp.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/seccomp.c b/kernel/seccomp.c index d7f5388..e815781 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -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 { -- 2.7.4