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869ae85dae
It is possible to expose non-zeroed post-EOF data in XFS if the new
EOF page is dirty, backed by an unwritten block and the truncate
happens to race with writeback. iomap_truncate_page() will not zero
the post-EOF portion of the page if the underlying block is
unwritten. The subsequent call to truncate_setsize() will, but
doesn't dirty the page. Therefore, if writeback happens to complete
after iomap_truncate_page() (so it still sees the unwritten block)
but before truncate_setsize(), the cached page becomes inconsistent
with the on-disk block. A mapped read after the associated page is
reclaimed or invalidated exposes non-zero post-EOF data.
For example, consider the following sequence when run on a kernel
modified to explicitly flush the new EOF page within the race
window:
$ xfs_io -fc "falloc 0 4k" -c fsync /mnt/file
$ xfs_io -c "pwrite 0 4k" -c "truncate 1k" /mnt/file
...
$ xfs_io -c "mmap 0 4k" -c "mread -v 1k 8" /mnt/file
00000400: 00 00 00 00 00 00 00 00 ........
$ umount /mnt/; mount <dev> /mnt/
$ xfs_io -c "mmap 0 4k" -c "mread -v 1k 8" /mnt/file
00000400: cd cd cd cd cd cd cd cd ........
Update xfs_setattr_size() to explicitly flush the new EOF page prior
to the page truncate to ensure iomap has the latest state of the
underlying block.
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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.