Levi Zim via B4 Relay wrote:
> From: Levi Zim <rsworktech@xxxxxxxxxxx>
>
> bpf kselftest sockhash::test_txmsg_cork_hangs in test_sockmap.c triggers a
> kernel NULL pointer dereference:
Is it just the cork test that causes issue?
>
> 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.
The intent was to ensure we allocate a buffer large enough to fit the
data. I guess the cork + send here is not allocating enough bytes?
>
> This commit changes it to use the real copied bytes.
>
> Signed-off-by: Levi Zim <rsworktech@xxxxxxxxxxx>
> ---
> net/ipv4/tcp_bpf.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
> index 370993c03d31363c0f82a003d9e5b0ca3bbed721..8e46c4d618cbbff0d120fe4cd917624e5d5cae15 100644
> --- a/net/ipv4/tcp_bpf.c
> +++ b/net/ipv4/tcp_bpf.c
> @@ -496,7 +496,7 @@ static int tcp_bpf_send_verdict(struct sock *sk, struct sk_psock *psock,
> static int tcp_bpf_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
> {
> struct sk_msg tmp, *msg_tx = NULL;
> - int copied = 0, err = 0;
> + int copied = 0, err = 0, ret = 0;
> struct sk_psock *psock;
> long timeo;
> int flags;
> @@ -539,14 +539,14 @@ static int tcp_bpf_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
> copy = msg_tx->sg.size - osize;
> }
>
> - err = sk_msg_memcopy_from_iter(sk, &msg->msg_iter, msg_tx,
> + ret = sk_msg_memcopy_from_iter(sk, &msg->msg_iter, msg_tx,
> copy);
> - if (err < 0) {
> + if (ret < 0) {
> sk_msg_trim(sk, msg_tx, osize);
> goto out_err;
> }
>
> - copied += copy;
> + copied += ret;
> if (psock->cork_bytes) {
> if (size > psock->cork_bytes)
> psock->cork_bytes = 0;
>
> --
> 2.47.1
>
>
