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rmap: anon_vma_prepare() can leak anon_vma_chain

PATCH In review Oleg Nesterov 2 participants 2 messages Apr 20, 2010 2 messages not in the archive

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Oleg Nesterov

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PATCH 1/1 rmap: anon_vma_prepare() can leak anon_vma_chain

In reply to a message not in the archive

If find_mergeable_anon_vma() succeeds but another thread installs ->anon_vma before we take ptl, then allocated == NULL but avc should be freed. Change the code to check avc != NULL to detect this case.

Also, a couple of whitespace changes to make the critical section more visible.

Signed-off-by Oleg Nesterov <[email protected]>

---

 mm/rmap.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)
mm/rmap.c renamed from mm/rmap.c~AVP_AVC_LEAK +5 -4
@@ -133,8 +133,8 @@ int anon_vma_prepare(struct vm_area_stru
 				goto out_enomem_free_avc;
 			allocated = anon_vma;
 		}
-		spin_lock(&anon_vma->lock);
 
+		spin_lock(&anon_vma->lock);
 		/* page_table_lock to protect against threads */
 		spin_lock(&mm->page_table_lock);
 		if (likely(!vma->anon_vma)) {

@@ -144,14 +144,15 @@ int anon_vma_prepare(struct vm_area_stru
 			list_add(&avc->same_vma, &vma->anon_vma_chain);
 			list_add(&avc->same_anon_vma, &anon_vma->head);
 			allocated = NULL;
+			avc = NULL;
 		}
 		spin_unlock(&mm->page_table_lock);
-
 		spin_unlock(&anon_vma->lock);
-		if (unlikely(allocated)) {
+
+		if (unlikely(allocated))
 			anon_vma_free(allocated);
+		if (unlikely(avc))
 			anon_vma_chain_free(avc);
-		}
 	}
 	return 0;