netdev - [PATCH net] net/bpfilter: initialize pos in __bpfilter_process

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Message-Id: <20200730160900.187157-1-hch@lst.de>
Date:   Thu, 30 Jul 2020 18:09:00 +0200
From:   Christoph Hellwig <hch@....de>
To:     davem@...emloft.net, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>,
        Rodrigo Madera <rodrigo.madera@...il.com>
Subject: [PATCH net] net/bpfilter: initialize pos in __bpfilter_process_sockopt

__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 <christian.brauner@...ntu.com>
Reported-by: Rodrigo Madera <rodrigo.madera@...il.com>
Signed-off-by: Christoph Hellwig <hch@....de>
Tested-by: Rodrigo Madera <rodrigo.madera@...il.com>
---
 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