linux-kernel - [PATCH 1/5] net: Fix potential deadloop in skb_copy

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Date:   Thu, 6 Aug 2020 19:50:42 +0800
From:   linmiaohe <linmiaohe@...wei.com>
To:     <davem@...emloft.net>, <pabeni@...hat.com>, <willemb@...gle.com>,
        <fw@...len.de>, <pablo@...filter.org>, <edumazet@...gle.com>,
        <steffen.klassert@...unet.com>, <Jason@...c4.com>,
        <rdunlap@...radead.org>, <decui@...rosoft.com>,
        <jakub@...udflare.com>, <jeremy@...zel.net>, <mashirle@...ibm.com>
CC:     <linux-kernel@...r.kernel.org>, <linmiaohe@...wei.com>
Subject: [PATCH 1/5] net: Fix potential deadloop in skb_copy_ubufs()

From: Miaohe Lin <linmiaohe@...wei.com>

We could be trapped in deadloop when we try to copy userspace skb frags
buffers to kernel with a cloned skb:

[kbox] catch panic event, panic reason:kernel stack overflow
[kbox] catch panic event, start logging.
CPU: 3 PID: 4083 Comm: insmod Kdump: loaded Tainted: G       OE  4.19 #6
Hardware name: linux,dummy-virt (DT)
Call trace:
	dump_backtrace+0x0/0x198
	show_stack+0x24/0x30
	dump_stack+0xa4/0xcc
	kbox_panic_notifier_callback+0x1d0/0x310 [kbox]
	notifier_call_chain+0x5c/0xa0
	atomic_notifier_call_chain+0x3c/0x50
	panic+0x164/0x314
	__stack_chk_fail+0x0/0x28
	handle_bad_stack+0xfc/0x108
	__bad_stack+0x90/0x94
	pskb_expand_head+0x0/0x2c8
	pskb_expand_head+0x290/0x2c8
	skb_copy_ubufs+0x3cc/0x520
	pskb_expand_head+0x290/0x2c8
	skb_copy_ubufs+0x3cc/0x520
	pskb_expand_head+0x290/0x2c8
	skb_copy_ubufs+0x3cc/0x520
	pskb_expand_head+0x290/0x2c8
	skb_copy_ubufs+0x3cc/0x520
	...
	pskb_expand_head+0x290/0x2c8
	skb_copy_ubufs+0x3cc/0x520
	...

Reproduce code snippet:
	skb = alloc_skb(UBUF_DATA_LEN, GFP_ATOMIC);
	clone = skb_clone(skb, GFP_ATOMIC);
	skb_zcopy_set_nouarg(clone, NULL);
	pskb_expand_head(skb, 0, 0, GFP_ATOMIC);

Catch this unexpected case and return -EINVAL in skb_orphan_frags() before
we call skb_copy_ubufs() to fix it.

Fixes: a6686f2f382b ("skbuff: skb supports zero-copy buffers")
Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 include/linux/skbuff.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 0c0377fc00c2..167c8f4cb6e3 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2753,6 +2753,9 @@ static inline int skb_orphan_frags(struct sk_buff *skb, gfp_t gfp_mask)
 	if (!skb_zcopy_is_nouarg(skb) &&
 	    skb_uarg(skb)->callback == sock_zerocopy_callback)
 		return 0;
+	/* If the skb is cloned, return error here or we will be trapped in deadloop. */
+	if (unlikely(skb_cloned(skb)))
+		return -EINVAL;
 	return skb_copy_ubufs(skb, gfp_mask);
 }
 
-- 
2.19.1