Re: [PATCH 2/3] mmap: Fix error paths with dup_anon_vma()

* Vlastimil Babka vbabka@suse.cz [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@vger.kernel.org Cc: Jann Horn jannh@google.com Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com

---

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);