Re: [PATCH] fsverity: RCU-delay the freeing of struct fsverity_info

[Eric Biggers <ebiggers@kernel.org>]

On Thu, Oct 01, 2026 at 10:13:49AM -0700, Eric Biggers wrote:
> __fsverity_get_info() calls rhashtable_lookup_fast(), which just uses
> rcu_read_lock() and doesn't directly synchronize with
> fsverity_remove_info().
> 
> For the same inode this isn't a problem: its fsverity_info is removed
> only at inode eviction time or upon failure to enable verity, when the
> inode no longer needs its fsverity_info and it will no longer be
> accessed via that inode.
> 
> However, this is broken and can cause a use-after-free for concurrent
> __fsverity_get_info() for *different* inodes.  Those rely on following
> fsverity_info::rhash_head in the rhashtable under rcu_read_lock() only.
> They also use fsverity_info::inode to do the key comparison.
> 
> Fix this by RCU-delaying the freeing of 'struct fsverity_info' after
> it's been removed from the rhashtable.
> 
> Fixes: f77f281b6118 ("fsverity: use a hashtable to find the fsverity_info")
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> ---
>  fs/verity/fsverity_private.h | 15 ++++++++++++++-
>  fs/verity/open.c             | 13 ++++++++++++-
>  2 files changed, 26 insertions(+), 2 deletions(-)

Applied to https://git.kernel.org/pub/scm/fs/fsverity/linux.git/log/?h=for-current

- Eric