* Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> [241206 16:52]: > 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> My cries to delete this optimisation continue. Reviewed-by: Liam R. Howlett <Liam.Howlett@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
