From 6668ed271eaefaa63e686bdfbedaeb7b8e492722 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Sep 2026 10:43:19 +0200 Subject: selftests/bpf: Reject graph kptr use after RCU unlock Add a sleepable verifier test that loads a graph-node local kptr in an explicit RCU read-side critical section, then passes its node to bpf_rbtree_remove() after the section ends. Before the verifier fix, the stale NON_OWN_REF flag makes the node look like a live borrowed reference and the program is accepted. After the fix, the pointer is demoted without NON_OWN_REF and the graph kfunc argument is rejected. Also exercise a graph kptr loaded while a spin lock provides implicit RCU protection. The pointer must be invalidated when the lock is released, which guards the required ordering between non-owning-reference invalidation and RCU demotion. Update the existing fault-protected load test state description. The post-unlock pointer no longer carries NON_OWN_REF, but remains readable because the load is rewritten to use BPF_PROBE_MEM. Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com Signed-off-by: Alexei Starovoitov --- fs/btrfs/lru_cache.h | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 71 insertions(+) create mode 100644 fs/btrfs/lru_cache.h (limited to 'fs/btrfs/lru_cache.h') diff --git a/fs/btrfs/lru_cache.h b/fs/btrfs/lru_cache.h new file mode 100644 index 000000000..07f1bb1c6 --- /dev/null +++ b/fs/btrfs/lru_cache.h @@ -0,0 +1,71 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef BTRFS_LRU_CACHE_H +#define BTRFS_LRU_CACHE_H + +#include +#include +#include + +/* + * A cache entry. This is meant to be embedded in a structure of a user of + * this module. Similar to how struct list_head and struct rb_node are used. + * + * Note: it should be embedded as the first element in a struct (offset 0), and + * this module assumes it was allocated with kmalloc(), so it calls kfree() when + * it needs to free an entry. + */ +struct btrfs_lru_cache_entry { + struct list_head lru_list; + u64 key; + /* + * Optional generation associated to a key. Use 0 if not needed/used. + * Entries with the same key and different generations are stored in a + * linked list, so use this only for cases where there's a small number + * of different generations. + */ + u64 gen; + /* + * The maple tree uses unsigned long type for the keys, which is 32 bits + * on 32 bits systems, and 64 bits on 64 bits systems. So if we want to + * use something like inode numbers as keys, which are always a u64, we + * have to deal with this in a special way - we store the key in the + * entry itself, as a u64, and the values inserted into the maple tree + * are linked lists of entries - so in case we are on a 64 bits system, + * that list always has a single entry, while on 32 bits systems it + * may have more than one, with each entry having the same value for + * their lower 32 bits of the u64 key. + */ + struct list_head list; +}; + +struct btrfs_lru_cache { + struct list_head lru_list; + struct maple_tree entries; + /* Number of entries stored in the cache. */ + unsigned int size; + /* Maximum number of entries the cache can have. */ + unsigned int max_size; +}; + +#define btrfs_lru_cache_for_each_entry_safe(cache, entry, tmp) \ + list_for_each_entry_safe_reverse((entry), (tmp), &(cache)->lru_list, lru_list) + +static inline struct btrfs_lru_cache_entry *btrfs_lru_cache_lru_entry( + struct btrfs_lru_cache *cache) +{ + return list_first_entry_or_null(&cache->lru_list, + struct btrfs_lru_cache_entry, lru_list); +} + +void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size); +struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache, + u64 key, u64 gen); +int btrfs_lru_cache_store(struct btrfs_lru_cache *cache, + struct btrfs_lru_cache_entry *new_entry, + gfp_t gfp); +void btrfs_lru_cache_remove(struct btrfs_lru_cache *cache, + struct btrfs_lru_cache_entry *entry); +void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache); + +#endif -- cgit v1.3.1