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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , David Ahern Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Levi Zim Message-ID: <675695f1265b2_1abf20862@john.notmuch> In-Reply-To: <20241130-tcp-bpf-sendmsg-v1-2-bae583d014f3@outlook.com> References: <20241130-tcp-bpf-sendmsg-v1-0-bae583d014f3@outlook.com> <20241130-tcp-bpf-sendmsg-v1-2-bae583d014f3@outlook.com> Subject: RE: [PATCH net 2/2] tcp_bpf: fix copied value in tcp_bpf_sendmsg Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Levi Zim via B4 Relay wrote: > From: Levi Zim > > 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 > --- > 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 > >