On 9/27/23 18:07, Liam R. Howlett wrote:
> When the calling function fails after the dup_anon_vma(), the
> duplication of the anon_vma is not being undone. Add the necessary
> unlink_anon_vma() call to the error paths that are missing them.
>
> This issue showed up during inspection of the error path in vma_merge()
> for an unrelated vma iterator issue.
>
> Users may experience increased memory usage, which may be problematic as
> the failure would likely be caused by a low memory situation.
>
> Fixes: d4af56c5c7c6 ("mm: start tracking VMAs with maple tree")
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Jann Horn <jannh@xxxxxxxxxx>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
> mm/mmap.c | 20 ++++++++++++++------
> 1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index b5bc4ca9bdc4..2f0ee489db8a 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -587,7 +587,7 @@ static inline void vma_complete(struct vma_prepare *vp,
> * Returns: 0 on success.
> */
> static inline int dup_anon_vma(struct vm_area_struct *dst,
> - struct vm_area_struct *src)
> + struct vm_area_struct *src, struct vm_area_struct **dup)
> {
> /*
> * Easily overlooked: when mprotect shifts the boundary, make sure the
> @@ -597,6 +597,7 @@ static inline int dup_anon_vma(struct vm_area_struct *dst,
> if (src->anon_vma && !dst->anon_vma) {
> vma_assert_write_locked(dst);
> dst->anon_vma = src->anon_vma;
> + *dup = dst;
> return anon_vma_clone(dst, src);
So the code is simpler that way and seems current callers are fine, but
shouldn't we rather only assign *dup if the clone succeeds?
> }
>
> @@ -624,6 +625,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
> unsigned long start, unsigned long end, pgoff_t pgoff,
> struct vm_area_struct *next)
> {
> + struct vm_area_struct *anon_dup = NULL;
> bool remove_next = false;
> struct vma_prepare vp;
>
> @@ -633,7 +635,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
>
> remove_next = true;
> vma_start_write(next);
> - ret = dup_anon_vma(vma, next);
> + ret = dup_anon_vma(vma, next, &anon_dup);
> if (ret)
> return ret;
> }
> @@ -661,6 +663,8 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
> return 0;
>
> nomem:
> + if (anon_dup)
> + unlink_anon_vmas(anon_dup);
> return -ENOMEM;
> }
>
> @@ -860,6 +864,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> {
> struct vm_area_struct *curr, *next, *res;
> struct vm_area_struct *vma, *adjust, *remove, *remove2;
> + struct vm_area_struct *anon_dup = NULL;
> struct vma_prepare vp;
> pgoff_t vma_pgoff;
> int err = 0;
> @@ -927,18 +932,18 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> vma_start_write(next);
> remove = next; /* case 1 */
> vma_end = next->vm_end;
> - err = dup_anon_vma(prev, next);
> + err = dup_anon_vma(prev, next, &anon_dup);
> if (curr) { /* case 6 */
> vma_start_write(curr);
> remove = curr;
> remove2 = next;
> if (!next->anon_vma)
> - err = dup_anon_vma(prev, curr);
> + err = dup_anon_vma(prev, curr, &anon_dup);
> }
> } else if (merge_prev) { /* case 2 */
> if (curr) {
> vma_start_write(curr);
> - err = dup_anon_vma(prev, curr);
> + err = dup_anon_vma(prev, curr, &anon_dup);
> if (end == curr->vm_end) { /* case 7 */
> remove = curr;
> } else { /* case 5 */
> @@ -954,7 +959,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> vma_end = addr;
> adjust = next;
> adj_start = -(prev->vm_end - addr);
> - err = dup_anon_vma(next, prev);
> + err = dup_anon_vma(next, prev, &anon_dup);
> } else {
> /*
> * Note that cases 3 and 8 are the ONLY ones where prev
> @@ -1018,6 +1023,9 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
> return res;
>
> prealloc_fail:
> + if (anon_dup)
> + unlink_anon_vmas(anon_dup);
> +
> anon_vma_fail:
> if (merge_prev)
> vma_next(vmi);
