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use RCU when accessing the action chain, to avoid use after free in the traffic path when 'goto chain' is replaced on existing TC actions (see script below). Since the control action is read in the traffic path without holding the action spinlock, we need to explicitly ensure that a->goto_chain is not NULL before dereferencing (i.e it's not sufficient to rely on the value of TC_ACT_GOTO_CHAIN bits). Not doing so caused NULL dereferences in tcf_action_goto_chain_exec() when the following script: # tc chain add dev dd0 chain 42 ingress protocol ip flower \ > ip_proto udp action pass index 4 # tc filter add dev dd0 ingress protocol ip flower \ > ip_proto udp action csum udp goto chain 42 index 66 # tc chain del dev dd0 chain 42 ingress (start UDP traffic towards dd0) # tc action replace action csum udp pass index 66 was run repeatedly for several hours. Suggested-by: Cong Wang <xiyou.wangcong@gmail.com> Suggested-by: Vlad Buslov <vladbu@mellanox.com> Signed-off-by: Davide Caratti <dcaratti@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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 Restructured Text 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.