In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix invalid pointer dereference in __btrfs_run_delayed_refs()
In the beginning of the loop, we try to obtain a locked delayed ref head, if locked_ref is currently NULL, by calling btrfs_select_ref_head(), which can return an error pointer. If the error pointer is -EAGAIN we do a continue and go back to the beginning of the loop, which will not try again to call btrfs_select_ref_head() since locked_ref is no longer NULL but its ERR_PTR(-EAGAIN), and then we do:
spin_lock(&locked_ref->lock);
against a ERR_PTR(-EAGAIN) value, generating an invalid pointer dereference.
Fix this by ensuring that locked_ref is set to NULL when btrfs_select_ref_head() returns ERR_PTR(-EAGAIN) and incrementing count as well, to prevent infinite looping. We do this by doing a goto to the bottom of the loop that already sets locked_ref to NULL and does a cond_resched(), with an increment to count right before the goto. These measures were in place before the refactoring in commit 0110a4c43451 (btrfs: refactor __btrfs_run_delayed_refs loop) but were unintentionally lost afterwards.
References
- https://git.kernel.org/stable/c/015dc4a1e0c2cba551d4620eba13d26d5081dc34
- https://git.kernel.org/stable/c/3b15d02be05e74321adb1e0ae0cb4ccfba7c6cb1
- https://git.kernel.org/stable/c/486f8298b6188ff11ef1f4be7f1d5d2e4d1b1fae
- https://git.kernel.org/stable/c/65770111a2d47c2b15e20b2ba92bb12198f289d4
- https://git.kernel.org/stable/c/9faa6b69ad73f03c7bde53e07d75a28822dc9a1a
- https://git.kernel.org/stable/c/a71143590ce9764dbcb47617647592ff8b4d48bc
- https://git.kernel.org/stable/c/ba9fa2ff5981589bb49094d3358c339b37c47f53
- https://git.kernel.org/stable/c/c372ca227e16bace86f1df1fa4ae6849e2fcfa28