netdev - Re: [PATCH RFT v2] sh_eth: fix kernel oops in skb

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Date:	Tue, 27 Oct 2015 07:52:11 +0900
From:	Yasushi SHOJI <yashi@...ark-techno.com>
To:	sergei.shtylyov@...entembedded.com
Cc:	netdev@...r.kernel.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH RFT v2] sh_eth: fix kernel oops in skb_put()

Hi Sergei,

Thank you for your patch!

On Sun, 25 Oct 2015 07:42:33 +0900,
Sergei Shtylyov wrote:
> 
> In a low memory situation the following kernel oops occurs:
> 
> Unable to handle kernel NULL pointer dereference at virtual address 00000050
> pgd = 8490c000
> [00000050] *pgd=4651e831, *pte=00000000, *ppte=00000000
> Internal error: Oops: 17 [#1] PREEMPT ARM
> Modules linked in:
> CPU: 0    Not tainted  (3.4-at16 #9)
> PC is at skb_put+0x10/0x98
> LR is at sh_eth_poll+0x2c8/0xa10
> pc : [<8035f780>]    lr : [<8028bf50>]    psr: 60000113
> sp : 84eb1a90  ip : 84eb1ac8  fp : 84eb1ac4
> r10: 0000003f  r9 : 000005ea  r8 : 00000000
> r7 : 00000000  r6 : 940453b0  r5 : 00030000  r4 : 9381b180
> r3 : 00000000  r2 : 00000000  r1 : 000005ea  r0 : 00000000
> Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment user
> Control: 10c53c7d  Table: 4248c059  DAC: 00000015
> Process klogd (pid: 2046, stack limit = 0x84eb02e8)
> [...]
> 
> This is because netdev_alloc_skb() fails and 'mdp->rx_skbuff[entry]' is left
> NULL but sh_eth_rx() later uses it without checking. Add such check...
> 
> Reported-by: Yasushi SHOJI <yashi@...ark-techno.com>
> Signed-off-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
> 
> ---
> This patch is against DaveM's 'net.git' repo.
> 
>  drivers/net/ethernet/renesas/sh_eth.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: net/drivers/net/ethernet/renesas/sh_eth.c
> ===================================================================
> --- net.orig/drivers/net/ethernet/renesas/sh_eth.c
> +++ net/drivers/net/ethernet/renesas/sh_eth.c
> @@ -1481,6 +1481,7 @@ static int sh_eth_rx(struct net_device *
>  		if (mdp->cd->shift_rd0)
>  			desc_status >>= 16;
>  
> +		skb = mdp->rx_skbuff[entry];
>  		if (desc_status & (RD_RFS1 | RD_RFS2 | RD_RFS3 | RD_RFS4 |
>  				   RD_RFS5 | RD_RFS6 | RD_RFS10)) {
>  			ndev->stats.rx_errors++;
> @@ -1496,12 +1497,11 @@ static int sh_eth_rx(struct net_device *
>  				ndev->stats.rx_missed_errors++;
>  			if (desc_status & RD_RFS10)
>  				ndev->stats.rx_over_errors++;
> -		} else {
> +		} else	if (skb) {
>  			if (!mdp->cd->hw_swap)
>  				sh_eth_soft_swap(
>  					phys_to_virt(ALIGN(rxdesc->addr, 4)),
>  					pkt_len + 2);
> -			skb = mdp->rx_skbuff[entry];
>  			mdp->rx_skbuff[entry] = NULL;
>  			if (mdp->cd->rpadir)
>  				skb_reserve(skb, NET_IP_ALIGN);
> 

This certainly prevents from a bad access, however, some odd thing is
going on.  Once I hit a low memory situation with this patch, network
thorough-put and response is very bad.

telnet, ping, wget takes loong time.

PING 172.16.2.13 (172.16.2.13) 56(84) bytes of data.
64 bytes from 172.16.2.13: icmp_seq=5 ttl=64 time=0.223 ms
64 bytes from 172.16.2.13: icmp_seq=6 ttl=64 time=0.195 ms
64 bytes from 172.16.2.13: icmp_seq=7 ttl=64 time=0.203 ms
64 bytes from 172.16.2.13: icmp_seq=8 ttl=64 time=0.219 ms
64 bytes from 172.16.2.13: icmp_seq=9 ttl=64 time=0.165 ms
64 bytes from 172.16.2.13: icmp_seq=10 ttl=64 time=0.171 ms
64 bytes from 172.16.2.13: icmp_seq=1 ttl=64 time=9023 ms
64 bytes from 172.16.2.13: icmp_seq=2 ttl=64 time=8022 ms
64 bytes from 172.16.2.13: icmp_seq=3 ttl=64 time=7014 ms
64 bytes from 172.16.2.13: icmp_seq=4 ttl=64 time=6006 ms

I'll investigate it.
-- 
              yashi
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