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Ext4 will always create ext4 extended attributes which do not have a
value (where e_value_size is zero) with e_value_offs set to zero. In
most places e_value_offs will not be used in a substantive way if
e_value_size is zero.
There was one exception to this, which is in ext4_xattr_set_entry(),
where if there is a maliciously crafted file system where there is an
extended attribute with e_value_offs is non-zero and e_value_size is
0, the attempt to remove this xattr will result in a negative value
getting passed to memmove, leading to the following sadness:
[ 41.225365] EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null)
[ 44.538641] BUG: unable to handle kernel paging request at ffff9ec9a3000000
[ 44.538733] IP: __memmove+0x81/0x1a0
[ 44.538755] PGD 1249bd067 P4D 1249bd067 PUD 1249c1067 PMD 80000001230000e1
[ 44.538793] Oops: 0003 [#1] SMP PTI
[ 44.539074] CPU: 0 PID: 1470 Comm: poc Not tainted 4.16.0-rc1+ #1
...
[ 44.539475] Call Trace:
[ 44.539832] ext4_xattr_set_entry+0x9e7/0xf80
...
[ 44.539972] ext4_xattr_block_set+0x212/0xea0
...
[ 44.540041] ext4_xattr_set_handle+0x514/0x610
[ 44.540065] ext4_xattr_set+0x7f/0x120
[ 44.540090] __vfs_removexattr+0x4d/0x60
[ 44.540112] vfs_removexattr+0x75/0xe0
[ 44.540132] removexattr+0x4d/0x80
...
[ 44.540279] path_removexattr+0x91/0xb0
[ 44.540300] SyS_removexattr+0xf/0x20
[ 44.540322] do_syscall_64+0x71/0x120
[ 44.540344] entry_SYSCALL_64_after_hwframe+0x21/0x86
https://bugzilla.kernel.org/show_bug.cgi?id=199347
This addresses CVE-2018-10840.
Reported-by: "Xu, Wen" <wen.xu@gatech.edu>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@kernel.org
Fixes:
|
||
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| 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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.