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Lorenzo Stoakes 00ca0f2e86 mm/mempolicy: correctly update prev when policy is equal on mbind 
The refactoring in commit f4e9e0e694 ("mm/mempolicy: fix use-after-free
of VMA iterator") introduces a subtle bug which arises when attempting to
apply a new NUMA policy across a range of VMAs in mbind_range().

The refactoring passes a **prev pointer to keep track of the previous VMA
in order to reduce duplication, and in all but one case it keeps this
correctly updated.

The bug arises when a VMA within the specified range has an equivalent
policy as determined by mpol_equal() - which unlike other cases, does not
update prev.

This can result in a situation where, later in the iteration, a VMA is
found whose policy does need to change.  At this point, vma_merge() is
invoked with prev pointing to a VMA which is before the previous VMA.

Since vma_merge() discovers the curr VMA by looking for the one
immediately after prev, it will now be in a situation where this VMA is
incorrect and the merge will not proceed correctly.

This is checked in the VM_WARN_ON() invariant case with end >
curr->vm_end, which, if a merge is possible, results in a warning (if
CONFIG_DEBUG_VM is specified).

I note that vma_merge() performs these invariant checks only after
merge_prev/merge_next are checked, which is debatable as it hides this
issue if no merge is possible even though a buggy situation has arisen.

The solution is simply to update the prev pointer even when policies are
equal.

This caused a bug to arise in the 6.2.y stable tree, and this patch
resolves this bug.

Link: https://lkml.kernel.org/r/83f1d612acb519d777bebf7f3359317c4e7f4265.1682866629.git.lstoakes@gmail.com
Fixes: f4e9e0e694 ("mm/mempolicy: fix use-after-free of VMA iterator")
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
  Link: https://lore.kernel.org/oe-lkp/202304292203.44ddeff6-oliver.sang@intel.com
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 		2023-05-02 17:23:27 -07:00
Documentation * Improve AMX documentation along with example code 2023-04-28 09:32:34 -07:00
LICENSES
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arch Add support for new Linear Address Masking CPU feature. This is similar 2023-04-28 09:43:49 -07:00
block Driver core changes for 6.4-rc1 2023-04-27 11:53:57 -07:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto modules-6.4-rc1 2023-04-27 16:36:55 -07:00
drivers Add support for new Linear Address Masking CPU feature. This is similar 2023-04-28 09:43:49 -07:00
fs Add support for new Linear Address Masking CPU feature. This is similar 2023-04-28 09:43:49 -07:00
include Add support for new Linear Address Masking CPU feature. This is similar 2023-04-28 09:43:49 -07:00
init - Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of 2023-04-27 19:42:02 -07:00
io_uring Networking changes for 6.4. 2023-04-26 16:07:23 -07:00
ipc
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kernel relayfs: fix out-of-bounds access in relay_file_read 2023-05-02 17:23:27 -07:00
lib Mainly singleton patches all over the place. Series of note are: 2023-04-27 19:57:00 -07:00
mm mm/mempolicy: correctly update prev when policy is equal on mbind 2023-05-02 17:23:27 -07:00
net - Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of 2023-04-27 19:42:02 -07:00
rust
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samples - Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of 2023-04-27 19:42:02 -07:00
scripts Mainly singleton patches all over the place. Series of note are: 2023-04-27 19:57:00 -07:00
security - Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of 2023-04-27 19:42:02 -07:00
sound Mainly singleton patches all over the place. Series of note are: 2023-04-27 19:57:00 -07:00
tools Add support for new Linear Address Masking CPU feature. This is similar 2023-04-28 09:43:49 -07:00
usr
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virt
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.gitignore linux-kselftest-kunit-6.4-rc1 2023-04-24 12:31:32 -07:00
.mailmap Mainly singleton patches all over the place. Series of note are: 2023-04-27 19:57:00 -07:00
.rustfmt.toml
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COPYING
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CREDITS Char/Misc drivers for 6.4-rc1 2023-04-27 12:07:50 -07:00
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MAINTAINERS Mainly singleton patches all over the place. Series of note are: 2023-04-27 19:57:00 -07:00
Makefile
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README
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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.