linux-kernel - Re: [PATCH] net/core/skbuff.c: __netdev_alloc_skb fix when len is greater than KMALLOC_MAX

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Date:   Mon, 01 Mar 2021 16:40:36 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
        kuba@...nel.org, linmiaohe@...wei.com,
        Sabyrzhan Tasbolatov <snovitoll@...il.com>,
        Alexander Lobakin <alobakin@...me>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+80dccaee7c6630fa9dcf@...kaller.appspotmail.com
Subject: Re: [PATCH] net/core/skbuff.c: __netdev_alloc_skb fix when len is
 greater than KMALLOC_MAX_SIZE

Hi, thanks for your reply!

On Mon, 2021-03-01 at 14:09 +0100, Eric Dumazet wrote:
> 
> On 2/26/21 8:11 PM, Pavel Skripkin wrote:
> > 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.
> > 
> > static void *kmalloc_large_node(size_t size, gfp_t flags, int node)
> > {
> > 	struct page *page;
> > 	void *ptr = NULL;
> > 	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
> >  __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
> >  qrtr_tun_write_iter+0x11f/0x1a0 net/qrtr/tun.c:98
> >  call_write_iter include/linux/fs.h:1901 [inline]
> >  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
> >  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > 
> > Reported-by: syzbot+80dccaee7c6630fa9dcf@...kaller.appspotmail.com
> > Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
> > Change-Id: I480a6d6f818a4c0a387db0cd3f230b68a7daeb16
> > ---
> >  net/core/skbuff.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index 785daff48030..dc28c8f7bf5f 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -443,6 +443,9 @@ struct sk_buff *__netdev_alloc_skb(struct
> > net_device *dev, unsigned int len,
> >  	if (len <= SKB_WITH_OVERHEAD(1024) ||
> >  	    len > SKB_WITH_OVERHEAD(PAGE_SIZE) ||
> >  	    (gfp_mask & (__GFP_DIRECT_RECLAIM | GFP_DMA))) {
> > +		if (len > KMALLOC_MAX_SIZE)
> > +			return NULL;
> > +
> >  		skb = __alloc_skb(len, gfp_mask, SKB_ALLOC_RX,
> > NUMA_NO_NODE);
> >  		if (!skb)
> >  			goto skb_fail;
> > 
> 
> 
> No, please fix the offender instead.

Yesterday I already send newer patch version to Alexander Lobakin,
where I added __GFP_NOWARN in qrtr_endpoint_post(). I think, You can
check it in this thread. 

> 
> Offender tentative fix was in 
> 
> commit 2a80c15812372e554474b1dba0b1d8e467af295d
> Author: Sabyrzhan Tasbolatov <snovitoll@...il.com>
> Date:   Tue Feb 2 15:20:59 2021 +0600
> 
>     net/qrtr: restrict user-controlled length in
> qrtr_tun_write_iter()
> 

This patch fixes kzalloc() call, but the warning was caused by
__netdev_alloc_skb().  

> 
> qrtr maintainers have to tell us what is the maximum datagram length
> they need to support.
> 
> 
> 
With regards,
Pavel Skripkin