@@ -1,4 +1,5 @@
# SPDX-License-Identifier: GPL-2.0
obj-$(CONFIG_FS_VERITY) += hash_algs.o \
- init.o
+ init.o \
+ open.o
@@ -15,8 +15,7 @@
#define pr_fmt(fmt) "fs-verity: " fmt
#include <crypto/sha.h>
-#include <linux/fs.h>
-#include <uapi/linux/fsverity.h>
+#include <linux/fsverity.h>
struct ahash_request;
@@ -59,6 +58,40 @@ struct merkle_tree_params {
u64 level_start[FS_VERITY_MAX_LEVELS];
};
+/**
+ * fsverity_info - cached verity metadata for an inode
+ *
+ * When a verity file is first opened, an instance of this struct is allocated
+ * and stored in ->i_verity_info; it remains until the inode is evicted. It
+ * caches information about the Merkle tree that's needed to efficiently verify
+ * data read from the file. It also caches the file measurement. The Merkle
+ * tree pages themselves are not cached here, but the filesystem may cache them.
+ */
+struct fsverity_info {
+ struct merkle_tree_params tree_params;
+ u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
+ u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
+ const struct inode *inode;
+};
+
+/*
+ * Merkle tree properties. The file measurement is the hash of this structure.
+ */
+struct fsverity_descriptor {
+ __u8 version; /* must be 1 */
+ __u8 hash_algorithm; /* Merkle tree hash algorithm */
+ __u8 log_blocksize; /* log2 of size of data and tree blocks */
+ __u8 salt_size; /* size of salt in bytes; 0 if none */
+ __le32 sig_size; /* reserved, must be 0 */
+ __le64 data_size; /* size of file the Merkle tree is built over */
+ __u8 root_hash[64]; /* Merkle tree root hash */
+ __u8 salt[32]; /* salt prepended to each hashed block */
+ __u8 __reserved[144]; /* must be 0's */
+};
+
+/* Arbitrary limit to bound the kmalloc() size. Can be changed. */
+#define FS_VERITY_MAX_DESCRIPTOR_SIZE 16384
+
/* hash_algs.c */
extern struct fsverity_hash_alg fsverity_hash_algs[];
@@ -85,4 +118,21 @@ fsverity_msg(const struct inode *inode, const char *level,
#define fsverity_err(inode, fmt, ...) \
fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
+/* open.c */
+
+int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
+ const struct inode *inode,
+ unsigned int hash_algorithm,
+ unsigned int log_blocksize,
+ const u8 *salt, size_t salt_size);
+
+struct fsverity_info *fsverity_create_info(const struct inode *inode,
+ const void *desc, size_t desc_size);
+
+void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
+
+void fsverity_free_info(struct fsverity_info *vi);
+
+int __init fsverity_init_info_cache(void);
+
#endif /* _FSVERITY_PRIVATE_H */
@@ -33,8 +33,14 @@ void fsverity_msg(const struct inode *inode, const char *level,
static int __init fsverity_init(void)
{
+ int err;
+
fsverity_check_hash_algs();
+ err = fsverity_init_info_cache();
+ if (err)
+ return err;
+
pr_debug("Initialized fs-verity\n");
return 0;
}
new file mode 100644
@@ -0,0 +1,318 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/open.c: opening fs-verity files
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#include "fsverity_private.h"
+
+#include <linux/slab.h>
+
+static struct kmem_cache *fsverity_info_cachep;
+
+/**
+ * fsverity_init_merkle_tree_params() - initialize Merkle tree parameters
+ * @params: the parameters struct to initialize
+ * @inode: the inode for which the Merkle tree is being built
+ * @hash_algorithm: number of hash algorithm to use
+ * @log_blocksize: log base 2 of block size to use
+ * @salt: pointer to salt (optional)
+ * @salt_size: size of salt, possibly 0
+ *
+ * Validate the hash algorithm and block size, then compute the tree topology
+ * (num levels, num blocks in each level, etc.) and initialize @params.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
+ const struct inode *inode,
+ unsigned int hash_algorithm,
+ unsigned int log_blocksize,
+ const u8 *salt, size_t salt_size)
+{
+ const struct fsverity_hash_alg *hash_alg;
+ int err;
+ u64 blocks;
+ u64 offset;
+ int level;
+
+ memset(params, 0, sizeof(*params));
+
+ hash_alg = fsverity_get_hash_alg(inode, hash_algorithm);
+ if (IS_ERR(hash_alg))
+ return PTR_ERR(hash_alg);
+ params->hash_alg = hash_alg;
+ params->digest_size = hash_alg->digest_size;
+
+ params->hashstate = fsverity_prepare_hash_state(hash_alg, salt,
+ salt_size);
+ if (IS_ERR(params->hashstate)) {
+ err = PTR_ERR(params->hashstate);
+ params->hashstate = NULL;
+ fsverity_err(inode, "Error %d preparing hash state", err);
+ goto out_err;
+ }
+
+ if (log_blocksize != PAGE_SHIFT) {
+ fsverity_warn(inode, "Unsupported log_blocksize: %u",
+ log_blocksize);
+ err = -EINVAL;
+ goto out_err;
+ }
+ params->log_blocksize = log_blocksize;
+ params->block_size = 1 << log_blocksize;
+
+ if (WARN_ON(!is_power_of_2(params->digest_size))) {
+ err = -EINVAL;
+ goto out_err;
+ }
+ if (params->block_size < 2 * params->digest_size) {
+ fsverity_warn(inode,
+ "Merkle tree block size (%u) too small for hash algorithm \"%s\"",
+ params->block_size, hash_alg->name);
+ err = -EINVAL;
+ goto out_err;
+ }
+ params->log_arity = params->log_blocksize - ilog2(params->digest_size);
+ params->hashes_per_block = 1 << params->log_arity;
+
+ pr_debug("Merkle tree uses %s with %u-byte blocks (%u hashes/block), salt=%*phN\n",
+ hash_alg->name, params->block_size, params->hashes_per_block,
+ (int)salt_size, salt);
+
+ /*
+ * Compute the number of levels in the Merkle tree and create a map from
+ * level to the starting block of that level. Level 'num_levels - 1' is
+ * the root and is stored first. Level 0 is the level directly "above"
+ * the data blocks and is stored last.
+ */
+
+ /* Compute number of levels and the number of blocks in each level */
+ blocks = (inode->i_size + params->block_size - 1) >> log_blocksize;
+ pr_debug("Data is %lld bytes (%llu blocks)\n", inode->i_size, blocks);
+ while (blocks > 1) {
+ if (params->num_levels >= FS_VERITY_MAX_LEVELS) {
+ fsverity_err(inode, "Too many levels in Merkle tree");
+ err = -EINVAL;
+ goto out_err;
+ }
+ blocks = (blocks + params->hashes_per_block - 1) >>
+ params->log_arity;
+ /* temporarily using level_start[] to store blocks in level */
+ params->level_start[params->num_levels++] = blocks;
+ }
+
+ /* Compute the starting block of each level */
+ offset = 0;
+ for (level = (int)params->num_levels - 1; level >= 0; level--) {
+ blocks = params->level_start[level];
+ params->level_start[level] = offset;
+ pr_debug("Level %d is %llu blocks starting at index %llu\n",
+ level, blocks, offset);
+ offset += blocks;
+ }
+
+ params->tree_size = offset << log_blocksize;
+ return 0;
+
+out_err:
+ kfree(params->hashstate);
+ memset(params, 0, sizeof(*params));
+ return err;
+}
+
+/* Compute the file measurement by hashing the fsverity_descriptor. */
+static int compute_file_measurement(const struct fsverity_hash_alg *hash_alg,
+ const struct fsverity_descriptor *desc,
+ u8 *measurement)
+{
+ return fsverity_hash_buffer(hash_alg, desc, sizeof(*desc), measurement);
+}
+
+/*
+ * Validate the given fsverity_descriptor and create a new fsverity_info from
+ * it.
+ */
+struct fsverity_info *fsverity_create_info(const struct inode *inode,
+ const void *_desc, size_t desc_size)
+{
+ const struct fsverity_descriptor *desc = _desc;
+ struct fsverity_info *vi;
+ int err;
+
+ if (desc_size < sizeof(*desc)) {
+ fsverity_err(inode, "Unrecognized descriptor size: %zu bytes",
+ desc_size);
+ return ERR_PTR(-EINVAL);
+ }
+
+ if (desc->version != 1) {
+ fsverity_err(inode, "Unrecognized descriptor version: %u",
+ desc->version);
+ return ERR_PTR(-EINVAL);
+ }
+
+ if (desc->sig_size ||
+ memchr_inv(desc->__reserved, 0, sizeof(desc->__reserved))) {
+ fsverity_err(inode, "Reserved bits set in descriptor");
+ return ERR_PTR(-EINVAL);
+ }
+
+ if (desc->salt_size > sizeof(desc->salt)) {
+ fsverity_err(inode, "Invalid salt_size: %u", desc->salt_size);
+ return ERR_PTR(-EINVAL);
+ }
+
+ if (le64_to_cpu(desc->data_size) != inode->i_size) {
+ fsverity_err(inode,
+ "Wrong data_size: %llu (desc) != %lld (inode)",
+ le64_to_cpu(desc->data_size), inode->i_size);
+ return ERR_PTR(-EINVAL);
+ }
+
+ vi = kmem_cache_zalloc(fsverity_info_cachep, GFP_KERNEL);
+ if (!vi)
+ return ERR_PTR(-ENOMEM);
+ vi->inode = inode;
+
+ err = fsverity_init_merkle_tree_params(&vi->tree_params, inode,
+ desc->hash_algorithm,
+ desc->log_blocksize,
+ desc->salt, desc->salt_size);
+ if (err) {
+ fsverity_err(inode,
+ "Error %d initializing Merkle tree parameters",
+ err);
+ goto out;
+ }
+
+ memcpy(vi->root_hash, desc->root_hash, vi->tree_params.digest_size);
+
+ err = compute_file_measurement(vi->tree_params.hash_alg, desc,
+ vi->measurement);
+ if (err) {
+ fsverity_err(inode, "Error %d computing file measurement", err);
+ goto out;
+ }
+ pr_debug("Computed file measurement: %s:%*phN\n",
+ vi->tree_params.hash_alg->name,
+ vi->tree_params.digest_size, vi->measurement);
+out:
+ if (err) {
+ fsverity_free_info(vi);
+ vi = ERR_PTR(err);
+ }
+ return vi;
+}
+
+void fsverity_set_info(struct inode *inode, struct fsverity_info *vi)
+{
+ /*
+ * Multiple processes may race to set ->i_verity_info, so use cmpxchg.
+ * This pairs with the READ_ONCE() in fsverity_get_info().
+ */
+ if (cmpxchg(&inode->i_verity_info, NULL, vi) != NULL)
+ fsverity_free_info(vi);
+}
+
+void fsverity_free_info(struct fsverity_info *vi)
+{
+ if (!vi)
+ return;
+ kfree(vi->tree_params.hashstate);
+ kmem_cache_free(fsverity_info_cachep, vi);
+}
+
+/* Ensure the inode has an ->i_verity_info */
+static int ensure_verity_info(struct inode *inode)
+{
+ struct fsverity_info *vi = fsverity_get_info(inode);
+ struct fsverity_descriptor *desc;
+ int res;
+
+ if (vi)
+ return 0;
+
+ res = inode->i_sb->s_vop->get_verity_descriptor(inode, NULL, 0);
+ if (res < 0) {
+ fsverity_err(inode,
+ "Error %d getting verity descriptor size", res);
+ return res;
+ }
+ if (res > FS_VERITY_MAX_DESCRIPTOR_SIZE) {
+ fsverity_err(inode, "Verity descriptor is too large (%d bytes)",
+ res);
+ return -EMSGSIZE;
+ }
+ desc = kmalloc(res, GFP_KERNEL);
+ if (!desc)
+ return -ENOMEM;
+ res = inode->i_sb->s_vop->get_verity_descriptor(inode, desc, res);
+ if (res < 0) {
+ fsverity_err(inode, "Error %d reading verity descriptor", res);
+ goto out_free_desc;
+ }
+
+ vi = fsverity_create_info(inode, desc, res);
+ if (IS_ERR(vi)) {
+ res = PTR_ERR(vi);
+ goto out_free_desc;
+ }
+
+ fsverity_set_info(inode, vi);
+ res = 0;
+out_free_desc:
+ kfree(desc);
+ return res;
+}
+
+/**
+ * fsverity_file_open() - prepare to open a verity file
+ * @inode: the inode being opened
+ * @filp: the struct file being set up
+ *
+ * When opening a verity file, deny the open if it is for writing. Otherwise,
+ * set up the inode's ->i_verity_info if not already done.
+ *
+ * When combined with fscrypt, this must be called after fscrypt_file_open().
+ * Otherwise, we won't have the key set up to decrypt the verity metadata.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_file_open(struct inode *inode, struct file *filp)
+{
+ if (!IS_VERITY(inode))
+ return 0;
+
+ if (filp->f_mode & FMODE_WRITE) {
+ pr_debug("Denying opening verity file (ino %lu) for write\n",
+ inode->i_ino);
+ return -EPERM;
+ }
+
+ return ensure_verity_info(inode);
+}
+EXPORT_SYMBOL_GPL(fsverity_file_open);
+
+/**
+ * fsverity_cleanup_inode() - free the inode's verity info, if present
+ *
+ * Filesystems must call this on inode eviction to free ->i_verity_info.
+ */
+void fsverity_cleanup_inode(struct inode *inode)
+{
+ fsverity_free_info(inode->i_verity_info);
+ inode->i_verity_info = NULL;
+}
+EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
+
+int __init fsverity_init_info_cache(void)
+{
+ fsverity_info_cachep = KMEM_CACHE_USERCOPY(fsverity_info,
+ SLAB_RECLAIM_ACCOUNT,
+ measurement);
+ if (!fsverity_info_cachep)
+ return -ENOMEM;
+ return 0;
+}
new file mode 100644
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * fs-verity: read-only file-based authenticity protection
+ *
+ * This header declares the interface between the fs/verity/ support layer and
+ * filesystems that support fs-verity.
+ *
+ * Copyright 2019 Google LLC
+ */
+
+#ifndef _LINUX_FSVERITY_H
+#define _LINUX_FSVERITY_H
+
+#include <linux/fs.h>
+#include <uapi/linux/fsverity.h>
+
+/* Verity operations for filesystems */
+struct fsverity_operations {
+
+ /**
+ * Get the verity descriptor of the given inode.
+ *
+ * @inode: an inode with the S_VERITY flag set
+ * @buf: buffer in which to place the verity descriptor
+ * @bufsize: size of @buf, or 0 to retrieve the size only
+ *
+ * If bufsize == 0, then the size of the verity descriptor is returned.
+ * Otherwise the verity descriptor is written to 'buf' and its actual
+ * size is returned; -ERANGE is returned if it's too large. This may be
+ * called by multiple processes concurrently on the same inode.
+ *
+ * Return: the size on success, -errno on failure
+ */
+ int (*get_verity_descriptor)(struct inode *inode, void *buf,
+ size_t bufsize);
+};
+
+#ifdef CONFIG_FS_VERITY
+
+static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
+{
+ /* pairs with the cmpxchg() in fsverity_set_info() */
+ return READ_ONCE(inode->i_verity_info);
+}
+
+/* open.c */
+
+extern int fsverity_file_open(struct inode *inode, struct file *filp);
+extern void fsverity_cleanup_inode(struct inode *inode);
+
+#else /* !CONFIG_FS_VERITY */
+
+static inline struct fsverity_info *fsverity_get_info(const struct inode *inode)
+{
+ return NULL;
+}
+
+/* open.c */
+
+static inline int fsverity_file_open(struct inode *inode, struct file *filp)
+{
+ return IS_VERITY(inode) ? -EOPNOTSUPP : 0;
+}
+
+static inline void fsverity_cleanup_inode(struct inode *inode)
+{
+}
+
+#endif /* !CONFIG_FS_VERITY */
+
+#endif /* _LINUX_FSVERITY_H */