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__list_versions will first estimate the required space using the "dm_target_iterate(list_version_get_needed, &needed)" call and then will fill the space using the "dm_target_iterate(list_version_get_info, &iter_info)" call. Each of these calls locks the targets using the "down_read(&_lock)" and "up_read(&_lock)" calls, however between the first and second "dm_target_iterate" there is no lock held and the target modules can be loaded at this point, so the second "dm_target_iterate" call may need more space than what was the first "dm_target_iterate" returned. The code tries to handle this overflow (see the beginning of list_version_get_info), however this handling is incorrect. The code sets "param->data_size = param->data_start + needed" and "iter_info.end = (char *)vers+len" - "needed" is the size returned by the first dm_target_iterate call; "len" is the size of the buffer allocated by userspace. "len" may be greater than "needed"; in this case, the code will write up to "len" bytes into the buffer, however param->data_size is set to "needed", so it may write data past the param->data_size value. The ioctl interface copies only up to param->data_size into userspace, thus part of the result will be truncated. Fix this bug by setting "iter_info.end = (char *)vers + needed;" - this guarantees that the second "dm_target_iterate" call will write only up to the "needed" buffer and it will exit with "DM_BUFFER_FULL_FLAG" if it overflows the "needed" space - in this case, userspace will allocate a larger buffer and retry. Note that there is also a bug in list_version_get_needed - we need to add "strlen(tt->name) + 1" to the needed size, not "strlen(tt->name)". Cc: stable@vger.kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@kernel.org> |
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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.