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43fb2b30ee
Before the cited commit, the kernel unconditionally embedded SCM
credentials to skb for embryo sockets even when both the sender
and listener disabled SO_PASSCRED and SO_PASSPIDFD.
Now, the credentials are added to skb only when configured by the
sender or the listener.
However, as reported in the link below, it caused a regression for
some programs that assume credentials are included in every skb,
but sometimes not now.
The only problematic scenario would be that a socket starts listening
before setting the option. Then, there will be 2 types of non-small
race window, where a client can send skb without credentials, which
the peer receives as an "invalid" message (and aborts the connection
it seems ?):
Client Server
------ ------
s1.listen() <-- No SO_PASS{CRED,PIDFD}
s2.connect()
s2.send() <-- w/o cred
s1.setsockopt(SO_PASS{CRED,PIDFD})
s2.send() <-- w/ cred
or
Client Server
------ ------
s1.listen() <-- No SO_PASS{CRED,PIDFD}
s2.connect()
s2.send() <-- w/o cred
s3, _ = s1.accept() <-- Inherit cred options
s2.send() <-- w/o cred but not set yet
s3.setsockopt(SO_PASS{CRED,PIDFD})
s2.send() <-- w/ cred
It's unfortunate that buggy programs depend on the behaviour,
but let's restore the previous behaviour.
Fixes: 3f84d577b7 ("af_unix: Inherit sk_flags at connect().")
Reported-by: Jacek Łuczak <difrost.kernel@gmail.com>
Closes: https://lore.kernel.org/all/68d38b0b-1666-4974-85d4-15575789c8d4@gmail.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Tested-by: Christian Heusel <christian@heusel.eu>
Tested-by: André Almeida <andrealmeid@igalia.com>
Tested-by: Jacek Łuczak <difrost.kernel@gmail.com>
Link: https://patch.msgid.link/20250611202758.3075858-1-kuni1840@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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.