Linux kernel source tree
2d7b30aef3
There's a race in between the rxrpc I/O thread recording the end of the
receive phase of a call and recvmsg() examining the state of the call to
determine whether it has completed.
The problem is that call->_state records the I/O thread's view of the call,
not the application's view (which may lag), so that alone is not
sufficient. To this end, the application also checks whether there is
anything left in call->recvmsg_queue for it to pick up. The call must be
in state RXRPC_CALL_COMPLETE and the recvmsg_queue empty for the call to be
considered fully complete.
In rxrpc_input_queue_data(), the latest skbuff is added to the queue and
then, if it was marked as LAST_PACKET, the state is advanced... But this
is two separate operations with no locking around them.
As a consequence, the lack of locking means that sendmsg() can jump into
the gap on a service call and attempt to send the reply - but then get
rejected because the I/O thread hasn't advanced the state yet.
Simply flipping the order in which things are done isn't an option as that
impacts the client side, causing the checks in rxrpc_kernel_check_life() as
to whether the call is still alive to race instead.
Fix this by moving the update of call->_state inside the skb queue
spinlocked section where the packet is queued on the I/O thread side.
rxrpc's recvmsg() will then automatically sync against this because it has
to take the call->recvmsg_queue spinlock in order to dequeue the last
packet.
rxrpc's sendmsg() doesn't need amending as the app shouldn't be calling it
to send a reply until recvmsg() indicates it has returned all of the
request.
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.