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authorLorenzo Stoakes <lstoakes@gmail.com>2023-04-30 16:07:07 +0100
committerAndrew Morton <akpm@linux-foundation.org>2023-05-02 17:23:27 -0700
commit00ca0f2e86bf40b016a646e6323a8941a09cf106 (patch)
treec3a77c2377f4c9662143d1c095efbf71ebb2d67a /mm
parent43ec16f1450f4936025a9bdf1a273affdb9732c1 (diff)
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>
Diffstat (limited to 'mm')
-rw-r--r--mm/mempolicy.c4
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,