[PATCH net v5] skmsg: skip zero length skb in sk_msg_recvmsg

[PATCH net v5] skmsg: skip zero length skb in sk_msg_recvmsg

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

Run this BPF selftests (./test_progs -t sockmap_basic) on a Loongarch
platform, 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
   ... ...
   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=...)
Stack : ...
        ...
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: ...

---[ 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 crash happens every time when running sockmap_skb_verdict_shutdown
subtest in sockmap_basic.

This crash is because a NULL pointer is passed to page_address() in
sk_msg_recvmsg(). Due to the difference implementations depending on the
architecture, page_address(NULL) will trigger a panic on Loongarch
platform but not on X86 platform. So this bug was hidden on X86 platform
for a while, but now it is exposed on Loongarch platform.

The root cause is a zero length skb (skb->len == 0) is put on the queue.

This zero length skb is a TCP FIN packet, which is sent by shutdown(),
invoked in test_sockmap_skb_verdict_shutdown():

	shutdown(p1, SHUT_WR);

In this case, in sk_psock_skb_ingress_enqueue(), num_sge is zero, and no
page is put to this sge (see sg_set_page in sg_set_page), but this empty
sge is queued into ingress_msg list.

And in sk_msg_recvmsg(), this empty sge is used, and a NULL page is got by
sg_page(sge). Pass this NULL page to copy_page_to_iter(), which passes it
to kmap_local_page() and to page_address(), then kernel panics.

To solve this, we should skip this zero length skb. So in sk_msg_recvmsg(),
if copy is zero, that means it's a zero length skb, skip invoking
copy_page_to_iter(). We are using the EFAULT return triggered by
copy_page_to_iter to check for is_fin in tcp_bpf.c.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Suggested-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
v5:
 - update v5 as John suggested.
 - skmsg: skip zero length skb in sk_msg_recvmsg

v4:
 - skmsg: skip empty sge in sk_msg_recvmsg

v3:
 - skmsg: prevent empty ingress skb from enqueuing
   
v2:
 - skmsg: null check for sg_page in sk_msg_recvmsg
---
 net/core/skmsg.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index fd20aae30be2..bbf40b999713 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -434,7 +434,8 @@ int sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr *msg,
 			page = sg_page(sge);
 			if (copied + copy > len)
 				copy = len - copied;
-			copy = copy_page_to_iter(page, sge->offset, copy, iter);
+			if (copy)
+				copy = copy_page_to_iter(page, sge->offset, copy, iter);
 			if (!copy) {
 				copied = copied ? copied : -EFAULT;
 				goto out;
-- 
2.43.0

RE: [PATCH net v5] skmsg: skip zero length skb in sk_msg_recvmsg

[John Fastabend]

Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> Run this BPF selftests (./test_progs -t sockmap_basic) on a Loongarch
> platform, 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
>    ... ...
>    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=...)
> Stack : ...
>         ...
> 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: ...
> 
> ---[ 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 crash happens every time when running sockmap_skb_verdict_shutdown
> subtest in sockmap_basic.
> 
> This crash is because a NULL pointer is passed to page_address() in
> sk_msg_recvmsg(). Due to the difference implementations depending on the
> architecture, page_address(NULL) will trigger a panic on Loongarch
> platform but not on X86 platform. So this bug was hidden on X86 platform
> for a while, but now it is exposed on Loongarch platform.
> 
> The root cause is a zero length skb (skb->len == 0) is put on the queue.
> 
> This zero length skb is a TCP FIN packet, which is sent by shutdown(),
> invoked in test_sockmap_skb_verdict_shutdown():
> 
> 	shutdown(p1, SHUT_WR);
> 
> In this case, in sk_psock_skb_ingress_enqueue(), num_sge is zero, and no
> page is put to this sge (see sg_set_page in sg_set_page), but this empty
> sge is queued into ingress_msg list.
> 
> And in sk_msg_recvmsg(), this empty sge is used, and a NULL page is got by
> sg_page(sge). Pass this NULL page to copy_page_to_iter(), which passes it
> to kmap_local_page() and to page_address(), then kernel panics.
> 
> To solve this, we should skip this zero length skb. So in sk_msg_recvmsg(),
> if copy is zero, that means it's a zero length skb, skip invoking
> copy_page_to_iter(). We are using the EFAULT return triggered by
> copy_page_to_iter to check for is_fin in tcp_bpf.c.
> 
> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
> Suggested-by: John Fastabend <john.fastabend@gmail.com>
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> ---
> v5:
>  - update v5 as John suggested.
>  - skmsg: skip zero length skb in sk_msg_recvmsg
> 
> v4:
>  - skmsg: skip empty sge in sk_msg_recvmsg
> 
> v3:
>  - skmsg: prevent empty ingress skb from enqueuing
>    
> v2:
>  - skmsg: null check for sg_page in sk_msg_recvmsg
> ---
>  net/core/skmsg.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

I don't have any better ideas so lets use this.

Reviewed-by: John Fastabend <john.fastabend@gmail.com>

Re: [PATCH net v5] skmsg: skip zero length skb in sk_msg_recvmsg

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Wed,  3 Jul 2024 16:39:31 +0800 you wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> Run this BPF selftests (./test_progs -t sockmap_basic) on a Loongarch
> platform, 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
>    ... ...
>    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=...)
> Stack : ...
>         ...
> 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
> 
> [...]

Here is the summary with links:
  - [net,v5] skmsg: skip zero length skb in sk_msg_recvmsg
    https://git.kernel.org/bpf/bpf/c/f0c180256937

You are awesome, thank you!
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