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The ram pstore backend has always had the crash dumper frontend enabled unconditionally. However, it was possible to effectively disable it by setting a record_size=0. All the machinery would run (storing dumps to the temporary crash buffer), but 0 bytes would ultimately get stored due to there being no przs allocated for dumps. Commit89d328f637("pstore/ram: Correctly calculate usable PRZ bytes"), however, assumed that there would always be at least one allocated dprz for calculating the size of the temporary crash buffer. This was, of course, not the case when record_size=0, and would lead to a NULL deref trying to find the dprz buffer size: BUG: unable to handle kernel NULL pointer dereference at (null) ... IP: ramoops_probe+0x285/0x37e (fs/pstore/ram.c:808) cxt->pstore.bufsize = cxt->dprzs[0]->buffer_size; Instead, we need to only enable the frontends based on the success of the prz initialization and only take the needed actions when those zones are available. (This also fixes a possible error in detecting if the ftrace frontend should be enabled.) Reported-and-tested-by: Yaro Slav <yaro330@gmail.com> Fixes:89d328f637("pstore/ram: Correctly calculate usable PRZ bytes") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.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 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.