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rmap: anon_vma_prepare() can leak anon_vma_chain

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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]>
This commit is contained in:
Oleg Nesterov 2010-04-23 13:18:01 -04:00 • committed by Linus Torvalds
commit 31f2b0ebc0
1 changed files with 5 additions and 4 deletions
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9
mm/rmap.c
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@ -133,8 +133,8 @@ int anon_vma_prepare(struct vm_area_struct *vma)
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_struct *vma)
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;