93c99f21db
Let's say a socket send()s "hello" with MSG_OOB and "world" without flags,
>>> from socket import *
>>> c1, c2 = socketpair(AF_UNIX)
>>> c1.send(b'hello', MSG_OOB)
5
>>> c1.send(b'world')
5
and its peer recv()s "hell" and "o".
>>> c2.recv(10)
b'hell'
>>> c2.recv(1, MSG_OOB)
b'o'
Now the consumed OOB skb stays at the head of recvq to return a correct
value for ioctl(SIOCATMARK), which is broken now and fixed by a later
patch.
Then, if peer issues recv() with MSG_DONTWAIT, manage_oob() returns NULL,
so recv() ends up with -EAGAIN.
>>> c2.setblocking(False) # This causes -EAGAIN even with available data
>>> c2.recv(5)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
BlockingIOError: [Errno 11] Resource temporarily unavailable
However, next recv() will return the following available data, "world".
>>> c2.recv(5)
b'world'
When the consumed OOB skb is at the head of the queue, we need to fetch
the next skb to fix the weird behaviour.
Note that the issue does not happen without MSG_DONTWAIT because we can
retry after manage_oob().
This patch also adds a test case that covers the issue.
Without fix:
# RUN msg_oob.no_peek.ex_oob_break ...
# msg_oob.c:134:ex_oob_break:AF_UNIX :Resource temporarily unavailable
# msg_oob.c:135:ex_oob_break:Expected:ld
# msg_oob.c:137:ex_oob_break:Expected ret[0] (-1) == expected_len (2)
# ex_oob_break: Test terminated by assertion
# FAIL msg_oob.no_peek.ex_oob_break
not ok 8 msg_oob.no_peek.ex_oob_break
With fix:
# RUN msg_oob.no_peek.ex_oob_break ...
# OK msg_oob.no_peek.ex_oob_break
ok 8 msg_oob.no_peek.ex_oob_break
Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.