4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Nikolay Borisov nborisov@suse.com
[ Upstream commit 9ea2c7c9da13c9073e371c046cbbc45481ecb459 ]
When modifying a tree where the root is at BTRFS_MAX_LEVEL - 1 then the level variable is going to be 7 (this is the max height of the tree). On the other hand btrfs_cow_block is always called with "level + 1" as an index into the nodes and slots arrays. This leads to an out of bounds access. Admittdely this will be benign since an OOB access of the nodes array will likely read the 0th element from the slots array, which in this case is going to be 0 (since we start CoW at the top of the tree). The OOB access into the slots array in turn will read the 0th and 1st values of the locks array, which would both be 0 at the time. However, this benign behavior relies on the fact that the path being passed hasn't been initialised, if it has already been used to query a btree then it could potentially have populated the nodes/slots arrays.
Fix it by explicitly checking if we are at level 7 (the maximum allowed index in nodes/slots arrays) and explicitly call the CoW routine with NULL for parent's node/slot.
Signed-off-by: Nikolay Borisov nborisov@suse.com Fixes-coverity-id: 711515 Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/btrfs/ctree.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)
--- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -2760,6 +2760,8 @@ again: * contention with the cow code */ if (cow) { + bool last_level = (level == (BTRFS_MAX_LEVEL - 1)); + /* * if we don't really need to cow this block * then we don't want to set the path blocking, @@ -2784,9 +2786,13 @@ again: }
btrfs_set_path_blocking(p); - err = btrfs_cow_block(trans, root, b, - p->nodes[level + 1], - p->slots[level + 1], &b); + if (last_level) + err = btrfs_cow_block(trans, root, b, NULL, 0, + &b); + else + err = btrfs_cow_block(trans, root, b, + p->nodes[level + 1], + p->slots[level + 1], &b); if (err) { ret = err; goto done;