Re: [PATCH v3] net/core/skbuff: fix passing wrong size to __alloc_skb
From: Alexander Lobakin
Date: Sun Feb 28 2021 - 13:16:13 EST
From: Pavel Skripkin <paskripkin@xxxxxxxxx>
Date: 2021年2月27日 20:51:14 +0300
Hi,
>
syzbot found WARNING in __alloc_pages_nodemask()[1] when order >= MAX_ORDER.
>
It was caused by __netdev_alloc_skb(), which doesn't check len value after adding NET_SKB_PAD.
>
Order will be >= MAX_ORDER and passed to __alloc_pages_nodemask() if size > KMALLOC_MAX_SIZE.
>
Same happens in __napi_alloc_skb.
>
>
static void *kmalloc_large_node(size_t size, gfp_t flags, int node)
>
{
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struct page *page;
>
void *ptr = NULL;
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unsigned int order = get_order(size);
>
...
>
page = alloc_pages_node(node, flags, order);
>
...
>
>
[1] WARNING in __alloc_pages_nodemask+0x5f8/0x730 mm/page_alloc.c:5014
>
Call Trace:
>
__alloc_pages include/linux/gfp.h:511 [inline]
>
__alloc_pages_node include/linux/gfp.h:524 [inline]
>
alloc_pages_node include/linux/gfp.h:538 [inline]
>
kmalloc_large_node+0x60/0x110 mm/slub.c:3999
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__kmalloc_node_track_caller+0x319/0x3f0 mm/slub.c:4496
>
__kmalloc_reserve net/core/skbuff.c:150 [inline]
>
__alloc_skb+0x4e4/0x5a0 net/core/skbuff.c:210
>
__netdev_alloc_skb+0x70/0x400 net/core/skbuff.c:446
>
netdev_alloc_skb include/linux/skbuff.h:2832 [inline]
>
qrtr_endpoint_post+0x84/0x11b0 net/qrtr/qrtr.c:442
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qrtr_tun_write_iter+0x11f/0x1a0 net/qrtr/tun.c:98
>
call_write_iter include/linux/fs.h:1901 [inline]
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new_sync_write+0x426/0x650 fs/read_write.c:518
>
vfs_write+0x791/0xa30 fs/read_write.c:605
>
ksys_write+0x12d/0x250 fs/read_write.c:658
>
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
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entry_SYSCALL_64_after_hwframe+0x44/0xa9
Ah, by the way. Have you tried to seek for the root cause, why
a request for such insanely large (at least 4 Mib) skb happens
in QRTR? I don't believe it's intended to be like this.
Now I feel that silencing this error with early return isn't
really correct approach for this.
>
Reported-by: syzbot+80dccaee7c6630fa9dcf@xxxxxxxxxxxxxxxxxxxxxxxxx
>
Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>
>
>
---
>
Changes from v3:
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* Removed Change-Id and extra tabs in net/core/skbuff.c
>
>
Changes from v2:
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* Added length check to __napi_alloc_skb
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* Added unlikely() in checks
>
>
Change from v1:
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* Added length check to __netdev_alloc_skb
>
---
>
net/core/skbuff.c | 6 ++++++
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1 file changed, 6 insertions(+)
>
>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
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index 785daff48030..ec7ba8728b61 100644
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--- a/net/core/skbuff.c
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+++ b/net/core/skbuff.c
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@@ -443,6 +443,9 @@ struct sk_buff *__netdev_alloc_skb(struct net_device *dev, unsigned int len,
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if (len <= SKB_WITH_OVERHEAD(1024) ||
>
len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
>
(gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
>
+ if (unlikely(len > KMALLOC_MAX_SIZE))
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+ return NULL;
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+
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skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
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if (!skb)
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goto skb_fail;
>
@@ -517,6 +520,9 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
>
if (len <= SKB_WITH_OVERHEAD(1024) ||
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len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
>
(gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
>
+ if (unlikely(len > KMALLOC_MAX_SIZE))
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+ return NULL;
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+
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skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX, NUMA_NO_NODE);
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if (!skb)
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goto skb_fail;
>
--
>
2.25.1
Thanks,
Al