Description

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free warning in btrfs_get_or_create_delayed_node() Previously, btrfs_get_or_create_delayed_node() set the delayed_node's refcount before acquiring the root->delayed_nodes lock. Commit e8513c012de7 ("btrfs: implement ref_tracker for delayed_nodes") moved refcount_set inside the critical section, which means there is no longer a memory barrier between setting the refcount and setting btrfs_inode->delayed_node. Without that barrier, the stores to node->refs and btrfs_inode->delayed_node may become visible out of order. Another thread can then read btrfs_inode->delayed_node and attempt to increment a refcount that hasn't been set yet, leading to a refcounting bug and a use-after-free warning. The fix is to move refcount_set back to where it was to take advantage of the implicit memory barrier provided by lock acquisition. Because the allocations now happen outside of the lock's critical section, they can use GFP_NOFS instead of GFP_ATOMIC.

Weaknesses 1

Affected Products 5

References 2

• git.kernel.org https://git.kernel.org/stable/c/83f59076a1ae6f5c6845d6f7ed3a1a373d883684
  Patch
• git.kernel.org https://git.kernel.org/stable/c/c8385851a5435f4006281828d428e5d0b0bbf8af
  Patch

Remediation

• git.kernel.org https://git.kernel.org/stable/c/83f59076a1ae6f5c6845d6f7ed3a1a373d883684
  Patch
• git.kernel.org https://git.kernel.org/stable/c/c8385851a5435f4006281828d428e5d0b0bbf8af
  Patch