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| author | Lorenzo Stoakes <lstoakes@gmail.com> | 2023-04-30 16:07:07 +0100 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-05-02 17:23:27 -0700 |
| commit | 00ca0f2e86bf40b016a646e6323a8941a09cf106 (patch) | |
| tree | c3a77c2377f4c9662143d1c095efbf71ebb2d67a | |
| parent | 43ec16f1450f4936025a9bdf1a273affdb9732c1 (diff) | |
| download | lwn-00ca0f2e86bf40b016a646e6323a8941a09cf106.tar.gz lwn-00ca0f2e86bf40b016a646e6323a8941a09cf106.zip | |
mm/mempolicy: correctly update prev when policy is equal on mbind
The refactoring in commit f4e9e0e69468 ("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: f4e9e0e69468 ("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>
| -rw-r--r-- | mm/mempolicy.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 2068b594dc88..1756389a0609 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -808,8 +808,10 @@ static int mbind_range(struct vma_iterator *vmi, struct vm_area_struct *vma, vmstart = vma->vm_start; } - if (mpol_equal(vma_policy(vma), new_pol)) + if (mpol_equal(vma_policy(vma), new_pol)) { + *prev = vma; return 0; + } pgoff = vma->vm_pgoff + ((vmstart - vma->vm_start) >> PAGE_SHIFT); merged = vma_merge(vmi, vma->vm_mm, *prev, vmstart, vmend, vma->vm_flags, |