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When userspace is adding data to an RPC call for transmission, it must pass
MSG_MORE to sendmsg() if it intends to add more data in future calls to
sendmsg(). Calling sendmsg() without MSG_MORE being asserted closes the
transmission phase of the call (assuming sendmsg() adds all the data
presented) and further attempts to add more data should be rejected.
However, this is no longer the case. The change of call state that was
previously the guard got bumped over to the I/O thread, which leaves a
window for a repeat sendmsg() to insert more data. This previously went
unnoticed, but the more recent patch that changed the structures behind the
Tx queue added a warning:
WARNING: CPU: 3 PID: 6639 at net/rxrpc/sendmsg.c:296 rxrpc_send_data+0x3f2/0x860
and rejected the additional data, returning error EPROTO.
Fix this by adding a guard flag to the call, setting the flag when we queue
the final packet and then rejecting further attempts to add data with
EPROTO.
Fixes: 2d689424b6 ("rxrpc: Move call state changes from sendmsg to I/O thread")
Reported-by: syzbot+ff11be94dfcd7a5af8da@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/6757fb68.050a0220.2477f.005f.GAE@google.com/
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: syzbot+ff11be94dfcd7a5af8da@syzkaller.appspotmail.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Link: https://patch.msgid.link/2870480.1734037462@warthog.procyon.org.uk
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.