The patch titled
Subject: mm: correctly reference merged VMA
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-correctly-reference-merged-vma.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-correctly-reference-merged-vma.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Subject: mm: correctly reference merged VMA
Date: Fri, 6 Dec 2024 21:52:29 +0000
On second merge attempt on mmap() we incorrectly discard the possibly
merged VMA, resulting in a possible use-after-free (and most certainly a
reference to the wrong VMA) in this instance in the subsequent
__mmap_complete() invocation.
Correct this mistake by reassigning vma correctly if a merge succeeds in
this case.
Link: https://lkml.kernel.org/r/20241206215229.244413-1-lorenzo.stoakes@xxxxxxxxxx
Fixes: 5ac87a885aec ("mm: defer second attempt at merge on mmap()")
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
Reported-by: syzbot+91cf8da9401355f946c3@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/all/67536a25.050a0220.a30f1.0149.GAE@xxxxxxxxxx/
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vma.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/mm/vma.c~mm-correctly-reference-merged-vma
+++ a/mm/vma.c
@@ -2460,10 +2460,13 @@ unsigned long __mmap_region(struct file
/* If flags changed, we might be able to merge, so try again. */
if (map.retry_merge) {
+ struct vm_area_struct *merged;
VMG_MMAP_STATE(vmg, &map, vma);
vma_iter_config(map.vmi, map.addr, map.end);
- vma_merge_existing_range(&vmg);
+ merged = vma_merge_existing_range(&vmg);
+ if (merged)
+ vma = merged;
}
__mmap_complete(&map, vma);
_
Patches currently in -mm which might be from lorenzo.stoakes@xxxxxxxxxx are
docs-mm-add-vma-locks-documentation.patch
mm-reinstate-ability-to-map-write-sealed-memfd-mappings-read-only.patch
selftests-memfd-add-test-for-mapping-write-sealed-memfd-read-only.patch
mm-correctly-reference-merged-vma.patch
mm-enforce-__must_check-on-vma-merge-and-split.patch
mm-vma-move-brk-internals-to-mm-vmac.patch
mm-vma-move-brk-internals-to-mm-vmac-fix.patch
mm-vma-move-unmapped_area-internals-to-mm-vmac.patch
mm-abstract-get_arg_page-stack-expansion-and-mmap-read-lock.patch
mm-vma-move-stack-expansion-logic-to-mm-vmac.patch
mm-vma-move-__vm_munmap-to-mm-vmac.patch
selftests-mm-add-fork-cow-guard-page-test.patch
