__bpfilter_process_sockopt never initialized the pos variable passed to
the pipe write.  This has been mostly harmless in the past as pipes
ignore the offset, but the switch to kernel_write no verified the
position, which can lead to a failure depending on the exact stack
initialization patter.  Initialize the variable to zero to make
rw_verify_area happy.

Fixes: 6955a76fbcd5 ("bpfilter: switch to kernel_write")
Reported-by: Christian Brauner <redacted>
Reported-by: Rodrigo Madera <redacted>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Rodrigo Madera <redacted>
---
 net/bpfilter/bpfilter_kern.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
index 1905e01c3aa9a7..4494ea6056cdb8 100644
--- a/net/bpfilter/bpfilter_kern.c
+++ b/net/bpfilter/bpfilter_kern.c

@@ -39,7 +39,7 @@ static int __bpfilter_process_sockopt(struct sock *sk, int optname,
 {
 	struct mbox_request req;
 	struct mbox_reply reply;
-	loff_t pos;
+	loff_t pos = 0;
 	ssize_t n;
 	int ret = -EFAULT;
 

-- 
2.27.0