netdev - [PATCH net] net: qrtr: Fix an uninit variable access bug in qrtr_tx

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Date:   Mon, 3 Apr 2023 15:54:17 +0800
From:   Ziyang Xuan <william.xuanziyang@...wei.com>
To:     <mani@...nel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
        <kuba@...nel.org>, <pabeni@...hat.com>, <andersson@...nel.org>,
        <luca@...tu.xyz>, <linux-arm-msm@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: [PATCH net] net: qrtr: Fix an uninit variable access bug in qrtr_tx_resume()

Syzbot reported a bug as following:

=====================================================
BUG: KMSAN: uninit-value in qrtr_tx_resume+0x185/0x1f0 net/qrtr/af_qrtr.c:230
 qrtr_tx_resume+0x185/0x1f0 net/qrtr/af_qrtr.c:230
 qrtr_endpoint_post+0xf85/0x11b0 net/qrtr/af_qrtr.c:519
 qrtr_tun_write_iter+0x270/0x400 net/qrtr/tun.c:108
 call_write_iter include/linux/fs.h:2189 [inline]
 aio_write+0x63a/0x950 fs/aio.c:1600
 io_submit_one+0x1d1c/0x3bf0 fs/aio.c:2019
 __do_sys_io_submit fs/aio.c:2078 [inline]
 __se_sys_io_submit+0x293/0x770 fs/aio.c:2048
 __x64_sys_io_submit+0x92/0xd0 fs/aio.c:2048
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Uninit was created at:
 slab_post_alloc_hook mm/slab.h:766 [inline]
 slab_alloc_node mm/slub.c:3452 [inline]
 __kmem_cache_alloc_node+0x71f/0xce0 mm/slub.c:3491
 __do_kmalloc_node mm/slab_common.c:967 [inline]
 __kmalloc_node_track_caller+0x114/0x3b0 mm/slab_common.c:988
 kmalloc_reserve net/core/skbuff.c:492 [inline]
 __alloc_skb+0x3af/0x8f0 net/core/skbuff.c:565
 __netdev_alloc_skb+0x120/0x7d0 net/core/skbuff.c:630
 qrtr_endpoint_post+0xbd/0x11b0 net/qrtr/af_qrtr.c:446
 qrtr_tun_write_iter+0x270/0x400 net/qrtr/tun.c:108
 call_write_iter include/linux/fs.h:2189 [inline]
 aio_write+0x63a/0x950 fs/aio.c:1600
 io_submit_one+0x1d1c/0x3bf0 fs/aio.c:2019
 __do_sys_io_submit fs/aio.c:2078 [inline]
 __se_sys_io_submit+0x293/0x770 fs/aio.c:2048
 __x64_sys_io_submit+0x92/0xd0 fs/aio.c:2048
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

It is because that skb->len requires at least sizeof(struct qrtr_ctrl_pkt)
in qrtr_tx_resume(). And skb->len equals to size in qrtr_endpoint_post().
But size is less than sizeof(struct qrtr_ctrl_pkt) when qrtr_cb->type
equals to QRTR_TYPE_RESUME_TX in qrtr_endpoint_post() under the syzbot
scenario. This triggers the uninit variable access bug.

Add size check when qrtr_cb->type equals to QRTR_TYPE_RESUME_TX in
qrtr_endpoint_post() to fix the bug.

Fixes: 5fdeb0d372ab ("net: qrtr: Implement outgoing flow control")
Reported-by: syzbot+4436c9630a45820fda76@...kaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=c14607f0963d27d5a3d5f4c8639b500909e43540
Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>
---
 net/qrtr/af_qrtr.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/qrtr/af_qrtr.c b/net/qrtr/af_qrtr.c
index 3a70255c8d02..631e81a8a368 100644
--- a/net/qrtr/af_qrtr.c
+++ b/net/qrtr/af_qrtr.c
@@ -498,6 +498,10 @@ int qrtr_endpoint_post(struct qrtr_endpoint *ep, const void *data, size_t len)
 	if (!size || len != ALIGN(size, 4) + hdrlen)
 		goto err;
 
+	if (cb->type == QRTR_TYPE_RESUME_TX &&
+	    size < sizeof(struct qrtr_ctrl_pkt))
+		goto err;
+
 	if (cb->dst_port != QRTR_PORT_CTRL && cb->type != QRTR_TYPE_DATA &&
 	    cb->type != QRTR_TYPE_RESUME_TX)
 		goto err;
-- 
2.25.1