Re: AW: AW: PROBLEM: Kernel Oops in UDP stack

[Paolo Abeni]

On Wed, 2018-08-01 at 10:35 +0000, Marcel Hellwig wrote:
> > > [<c0228adc>] (udp_recvmsg+0x284/0x33c) from [<c02306e0>] (inet_recvmsg+0x38/0x4c): net/ipv4/udp.c:1234
> > 
> >              sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
> > 
> > Unaligned access trap (virtual address c14fe63a), so either sin or ip_hdr(skb) are not on a 32bit alignment
> > 
> > Can you produce the disassembly of the trapping instruction ?
> 
> https://gist.github.com/hellow554/6b11c6c0827d5db80a7e66f71f5636ff#file-net_uipv4_udp-lst-L1892-L1895
> 
> 		sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
> c0228ad8:	e5943080 	ldr	r3, [r4, #128]	; 0x80
> c0228adc:	e593300c 	ldr	r3, [r3, #12]
> c0228ae0: 	e5823004	str	r3, [r2, #4]

I *think* pskb_trim_rcsum() in __udp4_lib_rcv() can copy the ipv4
header to an unaligned address, for cloned skbs. If I understood
correctly the relevant socket is a mcast one, so cloned skbs can land
there.

Paolo