rmap: anon_vma_prepare() can leak anon_vma_chain
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]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Pete Zaitcev <[email protected]>
Cc: Borislav Petkov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/mm/rmap.c b/mm/rmap.c
index 526704e..07fc947 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -133,8 +133,8 @@
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 @@
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;
