fsverity updates for 6.4

Several cleanups and fixes for fs/verity/, including a couple minor
 fixes to the changes in 6.3 that added support for Merkle tree block
 sizes less than the page size.
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Merge tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux

Pull fsverity updates from Eric Biggers:
 "Several cleanups and fixes for fs/verity/, including a couple minor
  fixes to the changes in 6.3 that added support for Merkle tree block
  sizes less than the page size"

* tag 'fsverity-for-linus' of git://git.kernel.org/pub/scm/fs/fsverity/linux:
  fsverity: reject FS_IOC_ENABLE_VERITY on mode 3 fds
  fsverity: explicitly check for buffer overflow in build_merkle_tree()
  fsverity: use WARN_ON_ONCE instead of WARN_ON
  fs-verity: simplify sysctls with register_sysctl()
  fs/buffer.c: use b_folio for fsverity work

fs/buffer.c

@@ -308,20 +308,19 @@ static void verify_bh(struct work_struct *work)
 	struct buffer_head *bh = ctx->bh;
 	bool valid;
 
-	valid = fsverity_verify_blocks(page_folio(bh->b_page), bh->b_size,
-				       bh_offset(bh));
+	valid = fsverity_verify_blocks(bh->b_folio, bh->b_size, bh_offset(bh));
 	end_buffer_async_read(bh, valid);
 	kfree(ctx);
 }
 
 static bool need_fsverity(struct buffer_head *bh)
 {
-	struct page *page = bh->b_page;
-	struct inode *inode = page->mapping->host;
+	struct folio *folio = bh->b_folio;
+	struct inode *inode = folio->mapping->host;
 
 	return fsverity_active(inode) &&
 		/* needed by ext4 */
-		page->index < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
+		folio->index < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
 }
 
 static void decrypt_bh(struct work_struct *work)

fs/verity/enable.c

@@ -13,6 +13,7 @@
 
 struct block_buffer {
 	u32 filled;
+	bool is_root_hash;
 	u8 *data;
 };
 
@@ -24,6 +25,14 @@ static int hash_one_block(struct inode *inode,
 	struct block_buffer *next = cur + 1;
 	int err;
 
+	/*
+	 * Safety check to prevent a buffer overflow in case of a filesystem bug
+	 * that allows the file size to change despite deny_write_access(), or a
+	 * bug in the Merkle tree logic itself
+	 */
+	if (WARN_ON_ONCE(next->is_root_hash && next->filled != 0))
+		return -EINVAL;
+
 	/* Zero-pad the block if it's shorter than the block size. */
 	memset(&cur->data[cur->filled], 0, params->block_size - cur->filled);
 
@@ -97,6 +106,7 @@ static int build_merkle_tree(struct file *filp,
 		}
 	}
 	buffers[num_levels].data = root_hash;
+	buffers[num_levels].is_root_hash = true;
 
 	BUILD_BUG_ON(sizeof(level_offset) != sizeof(params->level_start));
 	memcpy(level_offset, params->level_start, sizeof(level_offset));
@@ -165,7 +175,7 @@ static int build_merkle_tree(struct file *filp,
 		}
 	}
 	/* The root hash was filled by the last call to hash_one_block(). */
-	if (WARN_ON(buffers[num_levels].filled != params->digest_size)) {
+	if (WARN_ON_ONCE(buffers[num_levels].filled != params->digest_size)) {
 		err = -EINVAL;
 		goto out;
 	}
@@ -277,7 +287,7 @@ static int enable_verity(struct file *filp,
 		fsverity_err(inode, "%ps() failed with err %d",
 			     vops->end_enable_verity, err);
 		fsverity_free_info(vi);
-	} else if (WARN_ON(!IS_VERITY(inode))) {
+	} else if (WARN_ON_ONCE(!IS_VERITY(inode))) {
 		err = -EINVAL;
 		fsverity_free_info(vi);
 	} else {
@@ -347,6 +357,13 @@ int fsverity_ioctl_enable(struct file *filp, const void __user *uarg)
 	err = file_permission(filp, MAY_WRITE);
 	if (err)
 		return err;
+	/*
+	 * __kernel_read() is used while building the Merkle tree.  So, we can't
+	 * allow file descriptors that were opened for ioctl access only, using
+	 * the special nonstandard access mode 3.  O_RDONLY only, please!
+	 */
+	if (!(filp->f_mode & FMODE_READ))
+		return -EBADF;
 
 	if (IS_APPEND(inode))
 		return -EPERM;

fs/verity/hash_algs.c

@@ -84,9 +84,9 @@ struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
 	}
 
 	err = -EINVAL;
-	if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm)))
+	if (WARN_ON_ONCE(alg->digest_size != crypto_ahash_digestsize(tfm)))
 		goto err_free_tfm;
-	if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm)))
+	if (WARN_ON_ONCE(alg->block_size != crypto_ahash_blocksize(tfm)))
 		goto err_free_tfm;
 
 	err = mempool_init_kmalloc_pool(&alg->req_pool, 1,

fs/verity/open.c

@@ -83,7 +83,7 @@ int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
 	params->log_blocks_per_page = PAGE_SHIFT - log_blocksize;
 	params->blocks_per_page = 1 << params->log_blocks_per_page;
 
-	if (WARN_ON(!is_power_of_2(params->digest_size))) {
+	if (WARN_ON_ONCE(!is_power_of_2(params->digest_size))) {
 		err = -EINVAL;
 		goto out_err;
 	}

fs/verity/signature.c

@@ -88,12 +88,6 @@ int fsverity_verify_signature(const struct fsverity_info *vi,
 #ifdef CONFIG_SYSCTL
 static struct ctl_table_header *fsverity_sysctl_header;
 
-static const struct ctl_path fsverity_sysctl_path[] = {
-	{ .procname = "fs", },
-	{ .procname = "verity", },
-	{ }
-};
-
 static struct ctl_table fsverity_sysctl_table[] = {
 	{
 		.procname       = "require_signatures",
@@ -109,8 +103,7 @@ static struct ctl_table fsverity_sysctl_table[] = {
 
 static int __init fsverity_sysctl_init(void)
 {
-	fsverity_sysctl_header = register_sysctl_paths(fsverity_sysctl_path,
-						       fsverity_sysctl_table);
+	fsverity_sysctl_header = register_sysctl("fs/verity", fsverity_sysctl_table);
 	if (!fsverity_sysctl_header) {
 		pr_err("sysctl registration failed!\n");
 		return -ENOMEM;

include/linux/fsverity.h

@@ -233,18 +233,18 @@ static inline int fsverity_ioctl_read_metadata(struct file *filp,
 static inline bool fsverity_verify_blocks(struct folio *folio, size_t len,
 					  size_t offset)
 {
-	WARN_ON(1);
+	WARN_ON_ONCE(1);
 	return false;
 }
 
 static inline void fsverity_verify_bio(struct bio *bio)
 {
-	WARN_ON(1);
+	WARN_ON_ONCE(1);
 }
 
 static inline void fsverity_enqueue_verify_work(struct work_struct *work)
 {
-	WARN_ON(1);
+	WARN_ON_ONCE(1);
 }
 
 #endif	/* !CONFIG_FS_VERITY */