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Date:   Sat, 29 Apr 2023 14:36:40 +0300
From:   Ido Schimmel <idosch@idosch.org>
To:     syzbot <syzbot+ef6edd9f1baaa54d6235@syzkaller.appspotmail.com>
Cc:     davem@davemloft.net, edumazet@google.com, glider@google.com,
        kuba@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, pabeni@redhat.com,
        syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [net?] KMSAN: uninit-value in ethnl_set_linkmodes (2)
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On Fri, Apr 28, 2023 at 08:11:48PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    81af97bdef5e printk: Export console trace point for kcsan/..
> git tree:       https://github.com/google/kmsan.git master
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=10d4b844280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=ee7e125556b25104
> dashboard link: https://syzkaller.appspot.com/bug?extid=ef6edd9f1baaa54d6235
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1543bf0c280000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=158f4664280000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/00b0f311889c/disk-81af97bd.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/a3291e9cce5a/vmlinux-81af97bd.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/09b5e66af8b4/bzImage-81af97bd.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+ef6edd9f1baaa54d6235@syzkaller.appspotmail.com
> 
> =====================================================
> BUG: KMSAN: uninit-value in ethnl_update_linkmodes net/ethtool/linkmodes.c:273 [inline]
> BUG: KMSAN: uninit-value in ethnl_set_linkmodes+0x190b/0x19d0 net/ethtool/linkmodes.c:333
>  ethnl_update_linkmodes net/ethtool/linkmodes.c:273 [inline]
>  ethnl_set_linkmodes+0x190b/0x19d0 net/ethtool/linkmodes.c:333
>  ethnl_default_set_doit+0x88d/0xde0 net/ethtool/netlink.c:640
>  genl_family_rcv_msg_doit net/netlink/genetlink.c:968 [inline]
>  genl_family_rcv_msg net/netlink/genetlink.c:1048 [inline]
>  genl_rcv_msg+0x141a/0x14c0 net/netlink/genetlink.c:1065
>  netlink_rcv_skb+0x3f8/0x750 net/netlink/af_netlink.c:2577
>  genl_rcv+0x40/0x60 net/netlink/genetlink.c:1076
>  netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
>  netlink_unicast+0xf41/0x1270 net/netlink/af_netlink.c:1365
>  netlink_sendmsg+0x127d/0x1430 net/netlink/af_netlink.c:1942
>  sock_sendmsg_nosec net/socket.c:724 [inline]
>  sock_sendmsg net/socket.c:747 [inline]
>  ____sys_sendmsg+0xa24/0xe40 net/socket.c:2501
>  ___sys_sendmsg+0x2a1/0x3f0 net/socket.c:2555
>  __sys_sendmsg net/socket.c:2584 [inline]
>  __do_sys_sendmsg net/socket.c:2593 [inline]
>  __se_sys_sendmsg net/socket.c:2591 [inline]
>  __x64_sys_sendmsg+0x36b/0x540 net/socket.c:2591
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Uninit was stored to memory at:
>  tun_get_link_ksettings+0x37/0x60 drivers/net/tun.c:3544
>  __ethtool_get_link_ksettings+0x17b/0x260 net/ethtool/ioctl.c:441
>  ethnl_set_linkmodes+0xee/0x19d0 net/ethtool/linkmodes.c:327
>  ethnl_default_set_doit+0x88d/0xde0 net/ethtool/netlink.c:640
>  genl_family_rcv_msg_doit net/netlink/genetlink.c:968 [inline]
>  genl_family_rcv_msg net/netlink/genetlink.c:1048 [inline]
>  genl_rcv_msg+0x141a/0x14c0 net/netlink/genetlink.c:1065
>  netlink_rcv_skb+0x3f8/0x750 net/netlink/af_netlink.c:2577
>  genl_rcv+0x40/0x60 net/netlink/genetlink.c:1076
>  netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
>  netlink_unicast+0xf41/0x1270 net/netlink/af_netlink.c:1365
>  netlink_sendmsg+0x127d/0x1430 net/netlink/af_netlink.c:1942
>  sock_sendmsg_nosec net/socket.c:724 [inline]
>  sock_sendmsg net/socket.c:747 [inline]
>  ____sys_sendmsg+0xa24/0xe40 net/socket.c:2501
>  ___sys_sendmsg+0x2a1/0x3f0 net/socket.c:2555
>  __sys_sendmsg net/socket.c:2584 [inline]
>  __do_sys_sendmsg net/socket.c:2593 [inline]
>  __se_sys_sendmsg net/socket.c:2591 [inline]
>  __x64_sys_sendmsg+0x36b/0x540 net/socket.c:2591
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Uninit was stored to memory at:
>  tun_set_link_ksettings+0x37/0x60 drivers/net/tun.c:3553
>  ethtool_set_link_ksettings+0x600/0x690 net/ethtool/ioctl.c:609
>  __dev_ethtool net/ethtool/ioctl.c:3024 [inline]
>  dev_ethtool+0x1db9/0x2a70 net/ethtool/ioctl.c:3078
>  dev_ioctl+0xb07/0x1270 net/core/dev_ioctl.c:524
>  sock_do_ioctl+0x295/0x540 net/socket.c:1213
>  sock_ioctl+0x729/0xd90 net/socket.c:1316
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:870 [inline]
>  __se_sys_ioctl+0x222/0x400 fs/ioctl.c:856
>  __x64_sys_ioctl+0x96/0xe0 fs/ioctl.c:856
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Local variable link_ksettings created at:
>  ethtool_set_link_ksettings+0x54/0x690 net/ethtool/ioctl.c:577
>  __dev_ethtool net/ethtool/ioctl.c:3024 [inline]
>  dev_ethtool+0x1db9/0x2a70 net/ethtool/ioctl.c:3078
> 
> CPU: 1 PID: 4952 Comm: syz-executor743 Not tainted 6.3.0-syzkaller-g81af97bdef5e #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
> =====================================================
> 
> 
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.

The problem seems to be that 'struct ethtool_link_ksettings::lanes' is
not initialized in load_link_ksettings_from_user(). We can zero it
there, but a more robust approach would be to initialize the structure
in ethtool_set_link_ksettings().

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git main

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From 409e045251b2b08871072e2697dc195450ef378a Mon Sep 17 00:00:00 2001
From: Ido Schimmel <idosch@nvidia.com>
Date: Sat, 29 Apr 2023 14:18:05 +0300
Subject: [PATCH] fix

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
---
 net/ethtool/ioctl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 59adc4e6e9ee..6bb778e10461 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -574,8 +574,8 @@ static int ethtool_get_link_ksettings(struct net_device *dev,
 static int ethtool_set_link_ksettings(struct net_device *dev,
 				      void __user *useraddr)
 {
+	struct ethtool_link_ksettings link_ksettings = {};
 	int err;
-	struct ethtool_link_ksettings link_ksettings;
 
 	ASSERT_RTNL();
 
-- 
2.40.0


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