* Vlastimil Babka <vbabka@xxxxxxx> [230929 06:08]:
> 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?
Fair point. I'll address this in v3.
>
> > }
> >
> > @@ -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);
>
