linux-kernel - Re: [PATCH net 0/2] Fix NPE discovered by running bpf kselftest

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Message-ID:
 <MEYP282MB23129373641D74DE831E07E9C6342@MEYP282MB2312.AUSP282.PROD.OUTLOOK.COM>
Date: Sun, 1 Dec 2024 09:42:08 +0800
From: Levi Zim <rsworktech@...look.com>
To: John Fastabend <john.fastabend@...il.com>,
 Jakub Sitnicki <jakub@...udflare.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, David Ahern <dsahern@...nel.org>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 0/2] Fix NPE discovered by running bpf kselftest

On 2024-11-30 21:38, Levi Zim via B4 Relay wrote:
> I found that bpf kselftest sockhash::test_txmsg_cork_hangs in
> test_sockmap.c triggers a kernel NULL pointer dereference:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000008
>   ? __die_body+0x6e/0xb0
>   ? __die+0x8b/0xa0
>   ? page_fault_oops+0x358/0x3c0
>   ? local_clock+0x19/0x30
>   ? lock_release+0x11b/0x440
>   ? kernelmode_fixup_or_oops+0x54/0x60
>   ? __bad_area_nosemaphore+0x4f/0x210
>   ? mmap_read_unlock+0x13/0x30
>   ? bad_area_nosemaphore+0x16/0x20
>   ? do_user_addr_fault+0x6fd/0x740
>   ? prb_read_valid+0x1d/0x30
>   ? exc_page_fault+0x55/0xd0
>   ? asm_exc_page_fault+0x2b/0x30
>   ? splice_to_socket+0x52e/0x630
>   ? shmem_file_splice_read+0x2b1/0x310
>   direct_splice_actor+0x47/0x70
>   splice_direct_to_actor+0x133/0x300
>   ? do_splice_direct+0x90/0x90
>   do_splice_direct+0x64/0x90
>   ? __ia32_sys_tee+0x30/0x30
>   do_sendfile+0x214/0x300
>   __se_sys_sendfile64+0x8e/0xb0
>   __x64_sys_sendfile64+0x25/0x30
>   x64_sys_call+0xb82/0x2840
>   do_syscall_64+0x75/0x110
>   entry_SYSCALL_64_after_hwframe+0x4b/0x53
>
> This is caused by tcp_bpf_sendmsg() returning a larger value(12289) than
> size(8192), which causes the while loop in splice_to_socket() to release
> an uninitialized pipe buf.
>
> The underlying cause is that this code assumes sk_msg_memcopy_from_iter()
> will copy all bytes upon success but it actually might only copy part of
> it.
I am not sure what Fixes tag I should put. Git blame leads me to a 
refactor commit
and I am not familiar with this part of code base. Any suggestions?
>
> This series change sk_msg_memcopy_from_iter() to return copied bytes on
> success and tcp_bpf_sendmsg() to use the real copied bytes instead of
> assuming all bytes gets copied.
>
> Signed-off-by: Levi Zim <rsworktech@...look.com>
> ---
> Levi Zim (2):
>        skmsg: return copied bytes in sk_msg_memcopy_from_iter
>        tcp_bpf: fix copied value in tcp_bpf_sendmsg
>
>   net/core/skmsg.c   | 5 +++--
>   net/ipv4/tcp_bpf.c | 8 ++++----
>   2 files changed, 7 insertions(+), 6 deletions(-)
> ---
> base-commit: f1cd565ce57760923d5e0fbd9e9914b415c0620a
> change-id: 20241130-tcp-bpf-sendmsg-ff3c9d84e693
>
> Best regards,