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Date:   Fri, 10 Aug 2018 07:36:04 +0200
From:   Steffen Klassert <steffen.klassert@secunet.com>
To:     bai <baijiaju1990@gmail.com>
CC:     <herbert@gondor.apana.org.au>, <davem@davemloft.net>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] net: xfrm: Two possible sleep-in-atomic-context bugs
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On Fri, Aug 10, 2018 at 10:02:42AM +0800, bai wrote:
> The code may sleep in interrupt handler.
> xfrm_trans_reinject() is an interrupt handler set in tasklet_init().
> The function call paths (from bottom to top) in Linux-4.16 are:
> 
> [FUNC] schedule_timeout
> net/core/sock.c, 2044: schedule_timeout in sock_wait_for_wmem
> net/core/sock.c, 2083: sock_wait_for_wmem in sock_alloc_send_pskb
> net/core/sock.c, 2102: sock_alloc_send_pskb in sock_alloc_send_skb
> net/ipv6/mcast.c, 1989: sock_alloc_send_skb in igmp6_send

igmp6_send calls sock_alloc_send_skb with 'noblock = 1',
this means that sock_wait_for_wmem is not executed in
sock_alloc_send_pskb.

> net/ipv6/mcast.c, 2391: igmp6_send in igmp6_join_group
> net/ipv6/mcast.c, 670: igmp6_join_group in igmp6_group_added
> net/ipv6/mcast.c, 914: igmp6_group_added in ipv6_dev_mc_inc
> net/ipv6/ndisc.c, 379: ipv6_dev_mc_inc in pndisc_constructor
> net/core/neighbour.c, 640: [FUNC_PTR]pndisc_constructor in pneigh_lookup
> net/ipv6/ip6_output.c, 483: pneigh_lookup in ip6_forward
> ./include/net/dst.h, 449: [FUNC_PTR]ip6_forward in dst_input
> net/ipv6/ip6_input.c, 71: dst_input in ip6_rcv_finish
> net/xfrm/xfrm_input.c, 511: [FUNC_PTR]ip6_rcv_finish in xfrm_trans_reinject
> 
> [FUNC] kmalloc(GFP_KERNEL)
> net/core/neighbour.c, 630: kmalloc in pneigh_lookup
> net/ipv6/ip6_output.c, 483: pneigh_lookup in ip6_forward

ip6_forward calls pneigh_lookup with 'creat = 0',
this means that pneigh_lookup does not do the kmalloc.

> ./include/net/dst.h, 449: [FUNC_PTR]ip6_forward in dst_input
> net/ipv6/ip6_input.c, 71: dst_input in ip6_rcv_finish
> net/xfrm/xfrm_input.c, 511: [FUNC_PTR]ip6_rcv_finish in xfrm_trans_reinject
> 
> Note that [FUNC_PTR] means a function pointer call is used.
> 
> I do not find a good way to fix them, so I only report.
> These possible bugs are found by my static analysis tool (DSAC) and checked
> by my code review.

Both codepaths are ok, maybe you should fix your tool ;-)