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, 191 insertions, 0 deletions

diff --git a/fs/verity/measure.c b/fs/verity/measure.c
new file mode 100644
index 000000000..68dfccb69
--- /dev/null
+++ b/fs/verity/measure.c
@@ -0,0 +1,191 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Ioctl to get a verity file's digest
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <linux/export.h>
+#include <linux/uaccess.h>
+
+/**
+ * fsverity_ioctl_measure() - get a verity file's digest
+ * @filp: file to get digest of
+ * @_uarg: user pointer to fsverity_digest
+ *
+ * Retrieve the file digest that the kernel is enforcing for reads from a verity
+ * file.  See the "FS_IOC_MEASURE_VERITY" section of
+ * Documentation/filesystems/fsverity.rst for the documentation.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_ioctl_measure(struct file *filp, void __user *_uarg)
+{
+	const struct inode *inode = file_inode(filp);
+	struct fsverity_digest __user *uarg = _uarg;
+	const struct fsverity_info *vi;
+	const struct fsverity_hash_alg *hash_alg;
+	struct fsverity_digest arg;
+
+	vi = fsverity_get_info(inode);
+	if (!vi)
+		return -ENODATA; /* not a verity file */
+	hash_alg = vi->tree_params.hash_alg;
+
+	/*
+	 * The user specifies the digest_size their buffer has space for; we can
+	 * return the digest if it fits in the available space.  We write back
+	 * the actual size, which may be shorter than the user-specified size.
+	 */
+
+	if (get_user(arg.digest_size, &uarg->digest_size))
+		return -EFAULT;
+	if (arg.digest_size < hash_alg->digest_size)
+		return -EOVERFLOW;
+
+	memset(&arg, 0, sizeof(arg));
+	arg.digest_algorithm = hash_alg - fsverity_hash_algs;
+	arg.digest_size = hash_alg->digest_size;
+
+	if (copy_to_user(uarg, &arg, sizeof(arg)))
+		return -EFAULT;
+
+	if (copy_to_user(uarg->digest, vi->file_digest, hash_alg->digest_size))
+		return -EFAULT;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(fsverity_ioctl_measure);
+
+/**
+ * fsverity_get_digest() - get a verity file's digest
+ * @inode: inode to get digest of
+ * @raw_digest: (out) the raw file digest
+ * @alg: (out) the digest's algorithm, as a FS_VERITY_HASH_ALG_* value
+ * @halg: (out) the digest's algorithm, as a HASH_ALGO_* value
+ *
+ * Retrieves the fsverity digest of the given file. The
+ * fsverity_ensure_verity_info() must be called on the inode beforehand;
+ * otherwise this function will not recognize when fsverity is enabled.
+ *
+ * The file's fsverity digest consists of @raw_digest in combination with either
+ * @alg or @halg.  (The caller can choose which one of @alg or @halg to use.)
+ *
+ * IMPORTANT: Callers *must* make use of one of the two algorithm IDs, since
+ * @raw_digest is meaningless without knowing which algorithm it uses!  fsverity
+ * provides no security guarantee for users who ignore the algorithm ID, even if
+ * they use the digest size (since algorithms can share the same digest size).
+ *
+ * Return: The size of the raw digest in bytes, or 0 if the file doesn't have
+ *	   fsverity enabled.
+ */
+int fsverity_get_digest(struct inode *inode,
+			u8 raw_digest[FS_VERITY_MAX_DIGEST_SIZE],
+			u8 *alg, enum hash_algo *halg)
+{
+	const struct fsverity_info *vi;
+	const struct fsverity_hash_alg *hash_alg;
+
+	vi = fsverity_get_info(inode);
+	if (!vi)
+		return 0; /* not a verity file */
+
+	hash_alg = vi->tree_params.hash_alg;
+	memcpy(raw_digest, vi->file_digest, hash_alg->digest_size);
+	if (alg)
+		*alg = hash_alg - fsverity_hash_algs;
+	if (halg)
+		*halg = hash_alg->algo_id;
+	return hash_alg->digest_size;
+}
+EXPORT_SYMBOL_GPL(fsverity_get_digest);
+
+#ifdef CONFIG_BPF_SYSCALL
+
+/* bpf kfuncs */
+__bpf_kfunc_start_defs();
+
+/**
+ * bpf_get_fsverity_digest: read fsverity digest of file
+ * @file: file to get digest from
+ * @digest_p: (out) dynptr for struct fsverity_digest
+ *
+ * Read fsverity_digest of *file* into *digest_ptr*.
+ *
+ * Return: 0 on success, a negative value on error.
+ */
+__bpf_kfunc int bpf_get_fsverity_digest(struct file *file, const struct bpf_dynptr *digest_p)
+{
+	const struct bpf_dynptr_kern *digest_ptr = (struct bpf_dynptr_kern *)digest_p;
+	const struct inode *inode = file_inode(file);
+	u64 dynptr_sz = __bpf_dynptr_size(digest_ptr);
+	struct fsverity_digest *arg;
+	const struct fsverity_info *vi;
+	const struct fsverity_hash_alg *hash_alg;
+	u64 out_digest_sz;
+
+	if (dynptr_sz < sizeof(struct fsverity_digest))
+		return -EINVAL;
+
+	arg = __bpf_dynptr_data_rw(digest_ptr, dynptr_sz);
+	if (!arg)
+		return -EINVAL;
+
+	if (!IS_ALIGNED((uintptr_t)arg, __alignof__(*arg)))
+		return -EINVAL;
+
+	vi = fsverity_get_info(inode);
+	if (!vi)
+		return -ENODATA; /* not a verity file */
+
+	hash_alg = vi->tree_params.hash_alg;
+
+	out_digest_sz = dynptr_sz - sizeof(struct fsverity_digest);
+	if (out_digest_sz < hash_alg->digest_size)
+		return -EOVERFLOW;
+
+	arg->digest_algorithm = hash_alg - fsverity_hash_algs;
+	arg->digest_size = hash_alg->digest_size;
+
+	/* copy digest */
+	memcpy(arg->digest, vi->file_digest, hash_alg->digest_size);
+
+	/* fill the extra buffer with zeros */
+	if (out_digest_sz > hash_alg->digest_size)
+		memset(arg->digest + hash_alg->digest_size, 0,
+		       out_digest_sz - hash_alg->digest_size);
+
+	return 0;
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(fsverity_set_ids)
+BTF_ID_FLAGS(func, bpf_get_fsverity_digest)
+BTF_KFUNCS_END(fsverity_set_ids)
+
+static int bpf_get_fsverity_digest_filter(const struct bpf_prog *prog, u32 kfunc_id)
+{
+	if (!btf_id_set8_contains(&fsverity_set_ids, kfunc_id))
+		return 0;
+
+	/* Only allow to attach from LSM hooks, to avoid recursion */
+	return prog->type != BPF_PROG_TYPE_LSM ? -EACCES : 0;
+}
+
+static const struct btf_kfunc_id_set bpf_fsverity_set = {
+	.owner = THIS_MODULE,
+	.set = &fsverity_set_ids,
+	.filter = bpf_get_fsverity_digest_filter,
+};
+
+void __init fsverity_init_bpf(void)
+{
+	register_btf_kfunc_id_set(BPF_PROG_TYPE_LSM, &bpf_fsverity_set);
+}
+
+#endif /* CONFIG_BPF_SYSCALL */