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Subject[ 04/42] btree: fix tree corruption in btree_get_prev()
3.4-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Roland Dreier <roland@purestorage.com>

commit cbf8ae32f66a9ceb8907ad9e16663c2a29e48990 upstream.

The memory the parameter __key points to is used as an iterator in
btree_get_prev(), so if we save off a bkey() pointer in retry_key and
then assign that to __key, we'll end up corrupting the btree internals
when we do eg

longcpy(__key, bkey(geo, node, i), geo->keylen);

to return the key value. What we should do instead is use longcpy() to
copy the key value that retry_key points to __key.

This can cause a btree to get corrupted by seemingly read-only
operations such as btree_for_each_safe.

[akpm@linux-foundation.org: avoid the double longcpy()]
Signed-off-by: Roland Dreier <roland@purestorage.com>
Acked-by: Joern Engel <joern@logfs.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
lib/btree.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/lib/btree.c
+++ b/lib/btree.c
@@ -319,8 +319,8 @@ void *btree_get_prev(struct btree_head *

if (head->height == 0)
return NULL;
-retry:
longcpy(key, __key, geo->keylen);
+retry:
dec_key(geo, key);

node = head->node;
@@ -351,7 +351,7 @@ retry:
}
miss:
if (retry_key) {
- __key = retry_key;
+ longcpy(key, retry_key, geo->keylen);
retry_key = NULL;
goto retry;
}



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