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From: Eric Dumazet To: Paolo Abeni , netdev@vger.kernel.org Cc: Jakub Kicinski , mptcp@lists.01.org References: <5370c0ae03449239e3d1674ddcfb090cf6f20abe.1606253206.git.pabeni@redhat.com> <665bb3a603afebdcc85878f6b45bcf0313607994.camel@redhat.com> <2ac90c38-c82a-8aeb-2c01-b44a6de1bf57@gmail.com> Message-ID: Date: Wed, 2 Dec 2020 17:45:59 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 12/2/20 5:32 PM, Eric Dumazet wrote: > > > On 12/2/20 5:30 PM, Eric Dumazet wrote: >> >> >> On 12/2/20 5:10 PM, Eric Dumazet wrote: >>> >>> >>> On 12/2/20 4:37 PM, Paolo Abeni wrote: >>>> On Wed, 2020-12-02 at 14:18 +0100, Eric Dumazet wrote: >>>>> >>>>> On 11/24/20 10:51 PM, Paolo Abeni wrote: >>>>>> We can enter the main mptcp_recvmsg() loop even when >>>>>> no subflows are connected. As note by Eric, that would >>>>>> result in a divide by zero oops on ack generation. >>>>>> >>>>>> Address the issue by checking the subflow status before >>>>>> sending the ack. >>>>>> >>>>>> Additionally protect mptcp_recvmsg() against invocation >>>>>> with weird socket states. >>>>>> >>>>>> v1 -> v2: >>>>>> - removed unneeded inline keyword - Jakub >>>>>> >>>>>> Reported-and-suggested-by: Eric Dumazet >>>>>> Fixes: ea4ca586b16f ("mptcp: refine MPTCP-level ack scheduling") >>>>>> Signed-off-by: Paolo Abeni >>>>>> --- >>>>>> net/mptcp/protocol.c | 67 ++++++++++++++++++++++++++++++++------------ >>>>>> 1 file changed, 49 insertions(+), 18 deletions(-) >>>>>> >>>>> >>>>> Looking at mptcp recvmsg(), it seems that a read(fd, ..., 0) will >>>>> trigger an infinite loop if there is available data in receive queue ? >>>> >>>> Thank you for looking into this! >>>> >>>> I can't reproduce the issue with the following packetdrill ?!? >>>> >>>> +0.0 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress) >>>> +0.1 > S 0:0(0) >>>> +0.1 < S. 0:0(0) ack 1 win 65535 >>>> +0.1 > . 1:1(0) ack 1 >>>> +0.1 fcntl(3, F_SETFL, O_RDWR) = 0 >>>> +0.1 < . 1:201(200) ack 1 win 225 >>>> +0.1 > . 1:1(0) ack 201 >>>> +0.1 read(3, ..., 0) = 0 >>>> >>>> The main recvmsg() loop is interrupted by the following check: >>>> >>>> if (copied >= target) >>>> break; >>> >>> @copied should be 0, and @target should be 1 >>> >>> Are you sure the above condition is triggering ? >>> >>> Maybe read(fd, ..., 0) does not reach recvmsg() at all. >> >> Yes, sock_read_iter() has a shortcut : >> >> if (!iov_iter_count(to)) /* Match SYS5 behaviour */ >> res = sock_recvmsg(sock, &msg, msg.msg_flags); > > No idea what went wrong with my copy/paste. > > The real code is more like : > > if (!iov_iter_count(to)) /* Match SYS5 behaviour */ > return 0; > Packetdrill recvmsg syntax would be something like +0 recvmsg(3, {msg_name(...)=..., msg_iov(1)=[{..., 0}], msg_flags=0 }, 0) = 0