selftests/bpf: Reject graph kptr use after RCU unlockgrafted

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 <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 291 insertions, 0 deletions

diff --git a/fs/crypto/keysetup_v1.c b/fs/crypto/keysetup_v1.c
new file mode 100644
index 000000000..87fe13ccb
--- /dev/null
+++ b/fs/crypto/keysetup_v1.c
@@ -0,0 +1,291 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Key setup for v1 encryption policies
+ *
+ * Copyright 2015, 2019 Google LLC
+ */
+
+/*
+ * This file implements compatibility functions for the original encryption
+ * policy version ("v1"), including:
+ *
+ * - Deriving per-file encryption keys using the AES-128-ECB based KDF
+ *   (rather than the new method of using HKDF-SHA512)
+ *
+ * - Retrieving fscrypt master keys from process-subscribed keyrings
+ *   (rather than the new method of using a filesystem-level keyring)
+ *
+ * - Handling policies with the DIRECT_KEY flag set using a master key table
+ *   (rather than the new method of implementing DIRECT_KEY with per-mode keys
+ *    managed alongside the master keys in the filesystem-level keyring)
+ */
+
+#include <crypto/aes.h>
+#include <crypto/utils.h>
+#include <keys/user-type.h>
+#include <linux/hashtable.h>
+
+#include "fscrypt_private.h"
+
+/* Table of keys referenced by DIRECT_KEY policies */
+static DEFINE_HASHTABLE(fscrypt_direct_keys, 6); /* 6 bits = 64 buckets */
+static DEFINE_SPINLOCK(fscrypt_direct_keys_lock);
+
+/*
+ * Search the current task's subscribed keyrings for a "logon" key with
+ * description prefix:descriptor, and if found acquire a read lock on it and
+ * return a pointer to its validated payload in *payload_ret.
+ */
+static struct key *
+find_and_lock_process_key(const char *prefix,
+			  const u8 descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE],
+			  unsigned int min_keysize,
+			  const struct fscrypt_key **payload_ret)
+{
+	char *description;
+	struct key *key;
+	const struct user_key_payload *ukp;
+	const struct fscrypt_key *payload;
+
+	description = kasprintf(GFP_KERNEL, "%s%*phN", prefix,
+				FSCRYPT_KEY_DESCRIPTOR_SIZE, descriptor);
+	if (!description)
+		return ERR_PTR(-ENOMEM);
+
+	key = request_key(&key_type_logon, description, NULL);
+	kfree(description);
+	if (IS_ERR(key))
+		return key;
+
+	down_read(&key->sem);
+	ukp = user_key_payload_locked(key);
+
+	if (!ukp) /* was the key revoked before we acquired its semaphore? */
+		goto invalid;
+
+	payload = (const struct fscrypt_key *)ukp->data;
+
+	if (ukp->datalen != sizeof(struct fscrypt_key) ||
+	    payload->size < 1 || payload->size > sizeof(payload->raw)) {
+		fscrypt_warn(NULL,
+			     "key with description '%s' has invalid payload",
+			     key->description);
+		goto invalid;
+	}
+
+	if (payload->size < min_keysize) {
+		fscrypt_warn(NULL,
+			     "key with description '%s' is too short (got %u bytes, need %u+ bytes)",
+			     key->description, payload->size, min_keysize);
+		goto invalid;
+	}
+
+	*payload_ret = payload;
+	return key;
+
+invalid:
+	up_read(&key->sem);
+	key_put(key);
+	return ERR_PTR(-ENOKEY);
+}
+
+/* Master key referenced by DIRECT_KEY policy */
+struct fscrypt_direct_key {
+	struct super_block		*dk_sb;
+	struct hlist_node		dk_node;
+	refcount_t			dk_refcount;
+	const struct fscrypt_mode	*dk_mode;
+	struct fscrypt_prepared_key	dk_key;
+	u8				dk_descriptor[FSCRYPT_KEY_DESCRIPTOR_SIZE];
+	u8				dk_raw[FSCRYPT_MAX_RAW_KEY_SIZE];
+};
+
+static void free_direct_key(struct fscrypt_direct_key *dk)
+{
+	if (dk) {
+		fscrypt_destroy_prepared_key(dk->dk_sb, &dk->dk_key);
+		kfree_sensitive(dk);
+	}
+}
+
+void fscrypt_put_direct_key(struct fscrypt_direct_key *dk)
+{
+	if (!refcount_dec_and_lock(&dk->dk_refcount, &fscrypt_direct_keys_lock))
+		return;
+	hash_del(&dk->dk_node);
+	spin_unlock(&fscrypt_direct_keys_lock);
+
+	free_direct_key(dk);
+}
+
+/*
+ * Find/insert the given key into the fscrypt_direct_keys table.  If found, it
+ * is returned with elevated refcount, and 'to_insert' is freed if non-NULL.  If
+ * not found, 'to_insert' is inserted and returned if it's non-NULL; otherwise
+ * NULL is returned.
+ */
+static struct fscrypt_direct_key *
+find_or_insert_direct_key(struct fscrypt_direct_key *to_insert,
+			  const u8 *raw_key,
+			  const struct fscrypt_inode_info *ci)
+{
+	unsigned long hash_key;
+	struct fscrypt_direct_key *dk;
+
+	/*
+	 * Careful: to avoid potentially leaking secret key bytes via timing
+	 * information, we must key the hash table by descriptor rather than by
+	 * raw key, and use crypto_memneq() when comparing raw keys.
+	 */
+
+	BUILD_BUG_ON(sizeof(hash_key) > FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	memcpy(&hash_key, ci->ci_policy.v1.master_key_descriptor,
+	       sizeof(hash_key));
+
+	spin_lock(&fscrypt_direct_keys_lock);
+	hash_for_each_possible(fscrypt_direct_keys, dk, dk_node, hash_key) {
+		if (memcmp(ci->ci_policy.v1.master_key_descriptor,
+			   dk->dk_descriptor, FSCRYPT_KEY_DESCRIPTOR_SIZE) != 0)
+			continue;
+		/* The sb is used at eviction time, so it must be the same. */
+		if (ci->ci_inode->i_sb != dk->dk_sb)
+			continue;
+		if (ci->ci_mode != dk->dk_mode)
+			continue;
+		if (!fscrypt_is_key_prepared(&dk->dk_key, ci))
+			continue;
+		if (crypto_memneq(raw_key, dk->dk_raw, ci->ci_mode->keysize))
+			continue;
+		/*
+		 * Use an existing prepared key with the same (descriptor, sb,
+		 * mode, inlinecrypt, raw_key) combination.
+		 */
+		refcount_inc(&dk->dk_refcount);
+		spin_unlock(&fscrypt_direct_keys_lock);
+		free_direct_key(to_insert);
+		return dk;
+	}
+	if (to_insert)
+		hash_add(fscrypt_direct_keys, &to_insert->dk_node, hash_key);
+	spin_unlock(&fscrypt_direct_keys_lock);
+	return to_insert;
+}
+
+/* Prepare to encrypt directly using the master key in the given mode */
+static struct fscrypt_direct_key *
+fscrypt_get_direct_key(const struct fscrypt_inode_info *ci, const u8 *raw_key)
+{
+	struct fscrypt_direct_key *dk;
+	int err;
+
+	/* Is there already a tfm for this key? */
+	dk = find_or_insert_direct_key(NULL, raw_key, ci);
+	if (dk)
+		return dk;
+
+	/* Nope, allocate one. */
+	dk = kzalloc_obj(*dk);
+	if (!dk)
+		return ERR_PTR(-ENOMEM);
+	dk->dk_sb = ci->ci_inode->i_sb;
+	refcount_set(&dk->dk_refcount, 1);
+	dk->dk_mode = ci->ci_mode;
+	err = fscrypt_prepare_key(&dk->dk_key, raw_key, ci);
+	if (err)
+		goto err_free_dk;
+	memcpy(dk->dk_descriptor, ci->ci_policy.v1.master_key_descriptor,
+	       FSCRYPT_KEY_DESCRIPTOR_SIZE);
+	memcpy(dk->dk_raw, raw_key, ci->ci_mode->keysize);
+
+	return find_or_insert_direct_key(dk, raw_key, ci);
+
+err_free_dk:
+	free_direct_key(dk);
+	return ERR_PTR(err);
+}
+
+/* v1 policy, DIRECT_KEY: use the master key directly */
+static int setup_v1_file_key_direct(struct fscrypt_inode_info *ci,
+				    const u8 *raw_master_key)
+{
+	struct fscrypt_direct_key *dk;
+
+	dk = fscrypt_get_direct_key(ci, raw_master_key);
+	if (IS_ERR(dk))
+		return PTR_ERR(dk);
+	ci->ci_direct_key = dk;
+	ci->ci_enc_key = dk->dk_key;
+	return 0;
+}
+
+/*
+ * v1 policy, !DIRECT_KEY: derive the file's encryption key.
+ *
+ * The v1 key derivation function generates the derived key by encrypting the
+ * master key with AES-128-ECB using the file's nonce as the AES key.  This
+ * provides a unique derived key with sufficient entropy for each inode.
+ * However, it's nonstandard, non-extensible, doesn't evenly distribute the
+ * entropy from the master key, and is trivially reversible: an attacker who
+ * compromises a derived key can "decrypt" it to get back to the master key,
+ * then derive any other key.  For all new code, use HKDF instead.
+ *
+ * The master key must be at least as long as the derived key.  If the master
+ * key is longer, then only the first ci->ci_mode->keysize bytes are used.
+ */
+static int setup_v1_file_key_derived(struct fscrypt_inode_info *ci,
+				     const u8 *raw_master_key)
+{
+	const unsigned int derived_keysize = ci->ci_mode->keysize;
+	u8 derived_key[FSCRYPT_MAX_RAW_KEY_SIZE];
+	struct aes_enckey aes;
+	int err;
+
+	if (WARN_ON_ONCE(derived_keysize > FSCRYPT_MAX_RAW_KEY_SIZE ||
+			 derived_keysize % AES_BLOCK_SIZE != 0))
+		return -EINVAL;
+
+	static_assert(FSCRYPT_FILE_NONCE_SIZE == AES_KEYSIZE_128);
+	aes_prepareenckey(&aes, ci->ci_nonce, FSCRYPT_FILE_NONCE_SIZE);
+	for (unsigned int i = 0; i < derived_keysize; i += AES_BLOCK_SIZE)
+		aes_encrypt(&aes, &derived_key[i], &raw_master_key[i]);
+
+	err = fscrypt_set_per_file_enc_key(ci, derived_key);
+
+	memzero_explicit(derived_key, sizeof(derived_key));
+	/* No need to zeroize 'aes', as its key is not secret. */
+	return err;
+}
+
+int fscrypt_setup_v1_file_key(struct fscrypt_inode_info *ci,
+			      const u8 *raw_master_key)
+{
+	if (ci->ci_policy.v1.flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY)
+		return setup_v1_file_key_direct(ci, raw_master_key);
+	else
+		return setup_v1_file_key_derived(ci, raw_master_key);
+}
+
+int
+fscrypt_setup_v1_file_key_via_subscribed_keyrings(struct fscrypt_inode_info *ci)
+{
+	const struct super_block *sb = ci->ci_inode->i_sb;
+	struct key *key;
+	const struct fscrypt_key *payload;
+	int err;
+
+	key = find_and_lock_process_key(FSCRYPT_KEY_DESC_PREFIX,
+					ci->ci_policy.v1.master_key_descriptor,
+					ci->ci_mode->keysize, &payload);
+	if (key == ERR_PTR(-ENOKEY) && sb->s_cop->legacy_key_prefix) {
+		key = find_and_lock_process_key(sb->s_cop->legacy_key_prefix,
+						ci->ci_policy.v1.master_key_descriptor,
+						ci->ci_mode->keysize, &payload);
+	}
+	if (IS_ERR(key))
+		return PTR_ERR(key);
+
+	err = fscrypt_setup_v1_file_key(ci, payload->raw);
+	up_read(&key->sem);
+	key_put(key);
+	return err;
+}