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When iterating over the ring buffer while the ring buffer is active, the writer can corrupt the reader. There's barriers to help detect this and handle it, but that code missed the case where the last event was at the very end of the page and has only 4 bytes left. The checks to detect the corruption by the writer to reads needs to see the length of the event. If the length in the first 4 bytes is zero then the length is stored in the second 4 bytes. But if the writer is in the process of updating that code, there's a small window where the length in the first 4 bytes could be zero even though the length is only 4 bytes. That will cause rb_event_length() to read the next 4 bytes which could happen to be off the allocated page. To protect against this, fail immediately if the next event pointer is less than 8 bytes from the end of the commit (last byte of data), as all events must be a minimum of 8 bytes anyway. Link: https://lore.kernel.org/all/20230905141245.26470-1-Tze-nan.Wu@mediatek.com/ Link: https://lore.kernel.org/linux-trace-kernel/20230907122820.0899019c@gandalf.local.home Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Reported-by: Tze-nan Wu <Tze-nan.Wu@mediatek.com> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> |
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| 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 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.