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47c460efc4
xfs: fix realtime geometry integer overflows While reading through the realtime geometry support code in xfsprogs, I noticed a discrepancy between the sb_rextslog computation used when writing out the superblock during mkfs and the validation code used in xfs_repair. This discrepancy would lead to system failure for a runt rt volume having more than 1 rt block but zero rt extents in length. Most people aren't going to configure a 1M extent size for their 360k rt floppy disk volume, but I did! In the process of studying that code, it occurred to me that there is a second bug in the computation -- the use of highbit32 for a 64-bit value means that the upper 32 bits are not considered in the search for a high bit. This causes the creation of a realtime summary file that is the wrong length. If rextents is a multiple of U32_MAX then this will appear to work fine because highbit32 returns -1 for an input of 0; but for all other cases the rt summary is undersized, leading to failures. Fix the first problem by standardizing the computation with a helper in libxfs; and the second problem by correcting the computation. This will cause any existing rt volumes larger than 2^32 blocks to fail validation but they probably were already crashing anyway. This has been lightly tested with fstests. Enjoy! Signed-off-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Chandan Babu R <chandanbabu@kernel.org> * tag 'fix-rtmount-overflows-6.8_2023-12-06' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux: xfs: don't allow overly small or large realtime volumes xfs: fix 32-bit truncation in xfs_compute_rextslog xfs: make rextslog computation consistent with mkfs
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.