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

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Message-Id: <20241130-tcp-bpf-sendmsg-v1-0-bae583d014f3@outlook.com>
Date: Sat, 30 Nov 2024 21:38:21 +0800
From: Levi Zim via B4 Relay <devnull+rsworktech.outlook.com@...nel.org>
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, Levi Zim <rsworktech@...look.com>
Subject: [PATCH net 0/2] Fix NPE discovered by running bpf kselftest

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.

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,
-- 
Levi Zim <rsworktech@...look.com>