linux-kernel - [PATCH] net: ipv4: ipmr: Prevent information leak in ipmr_sk

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Message-ID: <20251227073743.17272-1-alperyasinak1@gmail.com>
Date: Sat, 27 Dec 2025 10:37:42 +0300
From: Alper Ak <alperyasinak1@...il.com>
To: davem@...emloft.net,
	dsahern@...nel.org,
	edumazet@...gle.com,
	kuba@...nel.org
Cc: Alper Ak <alperyasinak1@...il.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Breno Leitao <leitao@...ian.org>,
	Willem de Bruijn <willemb@...gle.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] net: ipv4: ipmr: Prevent information leak in ipmr_sk_ioctl()

struct sioc_vif_req has a padding hole after the vifi field due to
alignment requirements. These padding bytes were uninitialized,
potentially leaking kernel stack memory to userspace when the
struct is copied via sock_ioctl_inout().

Reported by Smatch:
    net/ipv4/ipmr.c:1575 ipmr_sk_ioctl() warn: check that 'buffer'
    doesn't leak information (struct has a hole after 'vifi')

Fixes: e1d001fa5b47 ("net: ioctl: Use kernel memory on protocol ioctl callbacks")
Signed-off-by: Alper Ak <alperyasinak1@...il.com>
---
 net/ipv4/ipmr.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index ca9eaee4c2ef..18441fbe7ed7 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1571,6 +1571,7 @@ int ipmr_sk_ioctl(struct sock *sk, unsigned int cmd, void __user *arg)
 	/* These userspace buffers will be consumed by ipmr_ioctl() */
 	case SIOCGETVIFCNT: {
 		struct sioc_vif_req buffer;
+		memset(&buffer, 0, sizeof(buffer));
 
 		return sock_ioctl_inout(sk, cmd, arg, &buffer,
 				      sizeof(buffer));
-- 
2.43.0