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. Suggested-by: Jann Horn <jannh@xxxxxxxxxx> Reported-by: syzbot+91cf8da9401355f946c3@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/all/67536a25.050a0220.a30f1.0149.GAE@xxxxxxxxxx/ Fixes: 5ac87a885aec ("mm: defer second attempt at merge on mmap()") Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> --- mm/vma.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/vma.c b/mm/vma.c index 8a454a7bbc80..1ec349141f5e 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -2460,10 +2460,13 @@ unsigned long __mmap_region(struct file *file, unsigned long addr, /* 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); -- 2.47.1
