From e58c3805ed325fe2d4ae2dd467c0486cc860b733 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Thu, 1 Oct 2026 10:13:49 -0700 Subject: [PATCH] fsverity: RCU-delay the freeing of struct fsverity_info __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 Reviewed-by: Christoph Hellwig Reviewed-by: Sandeep Dhavale Link: https://patch.msgid.link/20261001171349.81454-1-ebiggers@kernel.org Signed-off-by: Eric Biggers --- fs/verity/fsverity_private.h | 15 ++++++++++++++- fs/verity/open.c | 13 ++++++++++++- 2 files changed, 26 insertions(+), 2 deletions(-) diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h index 881d46f25e08..6f85f63861aa 100644 --- a/fs/verity/fsverity_private.h +++ b/fs/verity/fsverity_private.h @@ -11,6 +11,7 @@ #define pr_fmt(fmt) "fs-verity: " fmt #include +#include #include /* @@ -76,7 +77,19 @@ struct merkle_tree_params { struct fsverity_info { struct rhash_head rhash_head; struct merkle_tree_params tree_params; - u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE]; + union { + u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE]; + + /* + * Used for final freeing of the struct, in which case root_hash + * is no longer needed. Specifically, the only fields needed + * besides the rcu_head are those needed by fsverity_free_info() + * itself, and those that can be accessed by fsverity_get_info() + * (rhash_head and inode) during the RCU-protected rhashtable + * chain search trying to find another inode's fsverity_info. + */ + struct rcu_head rcu_head; + }; u8 file_digest[FS_VERITY_MAX_DIGEST_SIZE]; struct inode *inode; unsigned long *hash_block_verified; diff --git a/fs/verity/open.c b/fs/verity/open.c index d0c56a7faa3b..52c8cd014921 100644 --- a/fs/verity/open.c +++ b/fs/verity/open.c @@ -399,11 +399,22 @@ void fsverity_free_info(struct fsverity_info *vi) kmem_cache_free(fsverity_info_cachep, vi); } +static void fsverity_free_info_rcu(struct rcu_head *head) +{ + fsverity_free_info(container_of(head, struct fsverity_info, rcu_head)); +} + void fsverity_remove_info(struct fsverity_info *vi) { rhashtable_remove_fast(&fsverity_info_hash, &vi->rhash_head, fsverity_info_hash_params); - fsverity_free_info(vi); + /* + * The freeing must be RCU-delayed because __fsverity_get_info() for a + * *different* inode's fsverity_info in the same rhashtable hash chain + * can still be accessing *this* fsverity_info's rhash_head and inode + * fields as part of the RCU-protected hash chain search. + */ + call_rcu(&vi->rcu_head, fsverity_free_info_rcu); } void fsverity_cleanup_inode(struct inode *inode)