072222b488
The current code assumes kcm users know they need to look for the strparser offset within their bpf program, which is not documented anywhere and examples laying around do not do. The actual recv function does handle the offset well, so we can create a temporary clone of the skb and pull that one up as required for parsing. The pull itself has a cost if we are pulling beyond the head data, measured to 2-3% latency in a noisy VM with a local client stressing that path. The clone's impact seemed too small to measure. This bug can be exhibited easily by implementing a "trivial" kcm parser taking the first bytes as size, and on the client sending at least two such packets in a single write(). Note that bpf sockmap has the same problem, both for parse and for recv, so it would pulling twice or a real pull within the strparser logic if anyone cares about that. Signed-off-by: Dominique Martinet <asmadeus@codewreck.org> 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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.