Re: [PATCH bpf-next v2 1/4] skmsg: null check for sg_page in sk_msg_recvmsg

[John Fastabend <john.fastabend@gmail.com>]

Eric Dumazet wrote:
> On Tue, Jun 25, 2024 at 10:25 AM Geliang Tang <geliang@kernel.org> wrote:
> >
> > From: Geliang Tang <tanggeliang@kylinos.cn>
> >
> > Run the following BPF selftests on Loongarch:
> >
> > ./test_progs -t sockmap_basic
> >
> > A Kernel panic occurs:
> >
> > '''
> >  Oops[#1]:
> >  CPU: 22 PID: 2824 Comm: test_progs Tainted: G           OE      6.10.0-rc2+ #18
> >  Hardware name: LOONGSON Dabieshan/Loongson-TC542F0, BIOS Loongson-UDK2018-V4.0.11
> >  pc 9000000004162774 ra 90000000048bf6c0 tp 90001000aa16c000 sp 90001000aa16fb90
> >  a0 0000000000000000 a1 0000000000000000 a2 0000000000000000 a3 90001000aa16fd70
> >  a4 0000000000000800 a5 0000000000000000 a6 000055557b63aae8 a7 00000000000000cf
> >  t0 0000000000000000 t1 0000000000004000 t2 0000000000000048 t3 0000000000000000
> >  t4 0000000000000001 t5 0000000000000002 t6 0000000000000001 t7 0000000000000002
> >  t8 0000000000000018 u0 9000000004856150 s9 0000000000000000 s0 0000000000000000
> >  s1 0000000000000000 s2 90001000aa16fd70 s3 0000000000000000 s4 0000000000000000
> >  s5 0000000000004000 s6 900010009284dc00 s7 0000000000000001 s8 900010009284dc00
> >     ra: 90000000048bf6c0 sk_msg_recvmsg+0x120/0x560
> >    ERA: 9000000004162774 copy_page_to_iter+0x74/0x1c0
> >   CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
> >   PRMD: 0000000c (PPLV0 +PIE +PWE)
> >   EUEN: 00000007 (+FPE +SXE +ASXE -BTE)
> >   ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
> >  ESTAT: 00010000 [PIL] (IS= ECode=1 EsubCode=0)
> >   BADV: 0000000000000040
> >   PRID: 0014c011 (Loongson-64bit, Loongson-3C5000)
> >  Modules linked in: bpf_testmod(OE) xt_CHECKSUM xt_MASQUERADE xt_conntrack
> >  Process test_progs (pid: 2824, threadinfo=0000000000863a31, task=000000001cba0874)
> >  Stack : 0000000000000001 fffffffffffffffc 0000000000000000 0000000000000000
> >          0000000000000018 0000000000000000 0000000000000000 90000000048bf6c0
> >          90000000052cd638 90001000aa16fd70 900010008bf51580 900010009284f000
> >          90000000049f2b90 900010009284f188 900010009284f178 90001000861d4780
> >          9000100084dccd00 0000000000000800 0000000000000007 fffffffffffffff2
> >          000000000453e92f 90000000049aae34 90001000aa16fd60 900010009284f000
> >          0000000000000000 0000000000000000 900010008bf51580 90000000049f2b90
> >          0000000000000001 0000000000000000 9000100084dc3a10 900010009284f1ac
> >          90001000aa16fd40 0000555559953278 0000000000000001 0000000000000000
> >          90001000aa16fdc8 9000000005a5a000 90001000861d4780 0000000000000800
> >          ...
> >  Call Trace:
> >  [<9000000004162774>] copy_page_to_iter+0x74/0x1c0
> >  [<90000000048bf6c0>] sk_msg_recvmsg+0x120/0x560
> >  [<90000000049f2b90>] tcp_bpf_recvmsg_parser+0x170/0x4e0
> >  [<90000000049aae34>] inet_recvmsg+0x54/0x100
> >  [<900000000481ad5c>] sock_recvmsg+0x7c/0xe0
> >  [<900000000481e1a8>] __sys_recvfrom+0x108/0x1c0
> >  [<900000000481e27c>] sys_recvfrom+0x1c/0x40
> >  [<9000000004c076ec>] do_syscall+0x8c/0xc0
> >  [<9000000003731da4>] handle_syscall+0xc4/0x160
> >
> >  Code: 0010b09b  440125a0  0011df8d <28c10364> 0012b70c  00133305  0013b1ac  0010dc84  00151585
> >
> >  ---[ end trace 0000000000000000 ]---
> >  Kernel panic - not syncing: Fatal exception
> >  Kernel relocated by 0x3510000
> >   .text @ 0x9000000003710000
> >   .data @ 0x9000000004d70000
> >   .bss  @ 0x9000000006469400
> >  ---[ end Kernel panic - not syncing: Fatal exception ]---
> > '''
> >
> > This is because "sg_page(sge)" is NULL in that case. This patch adds null
> > check for it in sk_msg_recvmsg() to fix this error.
> >
> > Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
> > Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> > ---
> >  net/core/skmsg.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> > index fd20aae30be2..bafcc1e2eadf 100644
> > --- a/net/core/skmsg.c
> > +++ b/net/core/skmsg.c
> > @@ -432,6 +432,8 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg,
> >                         sge = sk_msg_elem(msg_rx, i);
> >                         copy = sge->length;
> >                         page = sg_page(sge);
> > +                       if (!page)
> > +                               goto out;
> >                         if (copied + copy > len)
> >                                 copy = len - copied;
> >                         copy = copy_page_to_iter(page, sge->offset, copy, iter);
> > --
> > 2.43.0
> >
> 
> This looks pretty much random to me.
> 
> Please find the root cause, instead of desperately trying to fix 'tests'.

If this happens then either we put a bad msg_rx on the queue see a few lines
up and we need to sort out why that msg_rx was built. Or we walked off the
end of a scatter gather list and need to see why this test isn't sufficient?

  } while ((i != msg_rx->sg.end) && !sg_is_last(sge))

is this happening every time you run the command or did you run this for
a long iteration and eventually hit this? I don't see why this would be
specific to your arch though.