linuxdebug/fs/btrfs/verity.c

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2024-07-16 15:50:57 +02:00
// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/rwsem.h>
#include <linux/xattr.h>
#include <linux/security.h>
#include <linux/posix_acl_xattr.h>
#include <linux/iversion.h>
#include <linux/fsverity.h>
#include <linux/sched/mm.h>
#include "ctree.h"
#include "btrfs_inode.h"
#include "transaction.h"
#include "disk-io.h"
#include "locking.h"
/*
* Implementation of the interface defined in struct fsverity_operations.
*
* The main question is how and where to store the verity descriptor and the
* Merkle tree. We store both in dedicated btree items in the filesystem tree,
* together with the rest of the inode metadata. This means we'll need to do
* extra work to encrypt them once encryption is supported in btrfs, but btrfs
* has a lot of careful code around i_size and it seems better to make a new key
* type than try and adjust all of our expectations for i_size.
*
* Note that this differs from the implementation in ext4 and f2fs, where
* this data is stored as if it were in the file, but past EOF. However, btrfs
* does not have a widespread mechanism for caching opaque metadata pages, so we
* do pretend that the Merkle tree pages themselves are past EOF for the
* purposes of caching them (as opposed to creating a virtual inode).
*
* fs verity items are stored under two different key types on disk.
* The descriptor items:
* [ inode objectid, BTRFS_VERITY_DESC_ITEM_KEY, offset ]
*
* At offset 0, we store a btrfs_verity_descriptor_item which tracks the
* size of the descriptor item and some extra data for encryption.
* Starting at offset 1, these hold the generic fs verity descriptor.
* The latter are opaque to btrfs, we just read and write them as a blob for
* the higher level verity code. The most common descriptor size is 256 bytes.
*
* The merkle tree items:
* [ inode objectid, BTRFS_VERITY_MERKLE_ITEM_KEY, offset ]
*
* These also start at offset 0, and correspond to the merkle tree bytes.
* So when fsverity asks for page 0 of the merkle tree, we pull up one page
* starting at offset 0 for this key type. These are also opaque to btrfs,
* we're blindly storing whatever fsverity sends down.
*
* Another important consideration is the fact that the Merkle tree data scales
* linearly with the size of the file (with 4K pages/blocks and SHA-256, it's
* ~1/127th the size) so for large files, writing the tree can be a lengthy
* operation. For that reason, we guard the whole enable verity operation
* (between begin_enable_verity and end_enable_verity) with an orphan item.
* Again, because the data can be pretty large, it's quite possible that we
* could run out of space writing it, so we try our best to handle errors by
* stopping and rolling back rather than aborting the victim transaction.
*/
#define MERKLE_START_ALIGN 65536
/*
* Compute the logical file offset where we cache the Merkle tree.
*
* @inode: inode of the verity file
*
* For the purposes of caching the Merkle tree pages, as required by
* fs-verity, it is convenient to do size computations in terms of a file
* offset, rather than in terms of page indices.
*
* Use 64K to be sure it's past the last page in the file, even with 64K pages.
* That rounding operation itself can overflow loff_t, so we do it in u64 and
* check.
*
* Returns the file offset on success, negative error code on failure.
*/
static loff_t merkle_file_pos(const struct inode *inode)
{
u64 sz = inode->i_size;
u64 rounded = round_up(sz, MERKLE_START_ALIGN);
if (rounded > inode->i_sb->s_maxbytes)
return -EFBIG;
return rounded;
}
/*
* Drop all the items for this inode with this key_type.
*
* @inode: inode to drop items for
* @key_type: type of items to drop (BTRFS_VERITY_DESC_ITEM or
* BTRFS_VERITY_MERKLE_ITEM)
*
* Before doing a verity enable we cleanup any existing verity items.
* This is also used to clean up if a verity enable failed half way through.
*
* Returns number of dropped items on success, negative error code on failure.
*/
static int drop_verity_items(struct btrfs_inode *inode, u8 key_type)
{
struct btrfs_trans_handle *trans;
struct btrfs_root *root = inode->root;
struct btrfs_path *path;
struct btrfs_key key;
int count = 0;
int ret;
path = btrfs_alloc_path();
if (!path)
return -ENOMEM;
while (1) {
/* 1 for the item being dropped */
trans = btrfs_start_transaction(root, 1);
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
goto out;
}
/*
* Walk backwards through all the items until we find one that
* isn't from our key type or objectid
*/
key.objectid = btrfs_ino(inode);
key.type = key_type;
key.offset = (u64)-1;
ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
if (ret > 0) {
ret = 0;
/* No more keys of this type, we're done */
if (path->slots[0] == 0)
break;
path->slots[0]--;
} else if (ret < 0) {
btrfs_end_transaction(trans);
goto out;
}
btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
/* No more keys of this type, we're done */
if (key.objectid != btrfs_ino(inode) || key.type != key_type)
break;
/*
* This shouldn't be a performance sensitive function because
* it's not used as part of truncate. If it ever becomes
* perf sensitive, change this to walk forward and bulk delete
* items
*/
ret = btrfs_del_items(trans, root, path, path->slots[0], 1);
if (ret) {
btrfs_end_transaction(trans);
goto out;
}
count++;
btrfs_release_path(path);
btrfs_end_transaction(trans);
}
ret = count;
btrfs_end_transaction(trans);
out:
btrfs_free_path(path);
return ret;
}
/*
* Drop all verity items
*
* @inode: inode to drop verity items for
*
* In most contexts where we are dropping verity items, we want to do it for all
* the types of verity items, not a particular one.
*
* Returns: 0 on success, negative error code on failure.
*/
int btrfs_drop_verity_items(struct btrfs_inode *inode)
{
int ret;
ret = drop_verity_items(inode, BTRFS_VERITY_DESC_ITEM_KEY);
if (ret < 0)
return ret;
ret = drop_verity_items(inode, BTRFS_VERITY_MERKLE_ITEM_KEY);
if (ret < 0)
return ret;
return 0;
}
/*
* Insert and write inode items with a given key type and offset.
*
* @inode: inode to insert for
* @key_type: key type to insert
* @offset: item offset to insert at
* @src: source data to write
* @len: length of source data to write
*
* Write len bytes from src into items of up to 2K length.
* The inserted items will have key (ino, key_type, offset + off) where off is
* consecutively increasing from 0 up to the last item ending at offset + len.
*
* Returns 0 on success and a negative error code on failure.
*/
static int write_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
const char *src, u64 len)
{
struct btrfs_trans_handle *trans;
struct btrfs_path *path;
struct btrfs_root *root = inode->root;
struct extent_buffer *leaf;
struct btrfs_key key;
unsigned long copy_bytes;
unsigned long src_offset = 0;
void *data;
int ret = 0;
path = btrfs_alloc_path();
if (!path)
return -ENOMEM;
while (len > 0) {
/* 1 for the new item being inserted */
trans = btrfs_start_transaction(root, 1);
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
break;
}
key.objectid = btrfs_ino(inode);
key.type = key_type;
key.offset = offset;
/*
* Insert 2K at a time mostly to be friendly for smaller leaf
* size filesystems
*/
copy_bytes = min_t(u64, len, 2048);
ret = btrfs_insert_empty_item(trans, root, path, &key, copy_bytes);
if (ret) {
btrfs_end_transaction(trans);
break;
}
leaf = path->nodes[0];
data = btrfs_item_ptr(leaf, path->slots[0], void);
write_extent_buffer(leaf, src + src_offset,
(unsigned long)data, copy_bytes);
offset += copy_bytes;
src_offset += copy_bytes;
len -= copy_bytes;
btrfs_release_path(path);
btrfs_end_transaction(trans);
}
btrfs_free_path(path);
return ret;
}
/*
* Read inode items of the given key type and offset from the btree.
*
* @inode: inode to read items of
* @key_type: key type to read
* @offset: item offset to read from
* @dest: Buffer to read into. This parameter has slightly tricky
* semantics. If it is NULL, the function will not do any copying
* and will just return the size of all the items up to len bytes.
* If dest_page is passed, then the function will kmap_local the
* page and ignore dest, but it must still be non-NULL to avoid the
* counting-only behavior.
* @len: length in bytes to read
* @dest_page: copy into this page instead of the dest buffer
*
* Helper function to read items from the btree. This returns the number of
* bytes read or < 0 for errors. We can return short reads if the items don't
* exist on disk or aren't big enough to fill the desired length. Supports
* reading into a provided buffer (dest) or into the page cache
*
* Returns number of bytes read or a negative error code on failure.
*/
static int read_key_bytes(struct btrfs_inode *inode, u8 key_type, u64 offset,
char *dest, u64 len, struct page *dest_page)
{
struct btrfs_path *path;
struct btrfs_root *root = inode->root;
struct extent_buffer *leaf;
struct btrfs_key key;
u64 item_end;
u64 copy_end;
int copied = 0;
u32 copy_offset;
unsigned long copy_bytes;
unsigned long dest_offset = 0;
void *data;
char *kaddr = dest;
int ret;
path = btrfs_alloc_path();
if (!path)
return -ENOMEM;
if (dest_page)
path->reada = READA_FORWARD;
key.objectid = btrfs_ino(inode);
key.type = key_type;
key.offset = offset;
ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
if (ret < 0) {
goto out;
} else if (ret > 0) {
ret = 0;
if (path->slots[0] == 0)
goto out;
path->slots[0]--;
}
while (len > 0) {
leaf = path->nodes[0];
btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
if (key.objectid != btrfs_ino(inode) || key.type != key_type)
break;
item_end = btrfs_item_size(leaf, path->slots[0]) + key.offset;
if (copied > 0) {
/*
* Once we've copied something, we want all of the items
* to be sequential
*/
if (key.offset != offset)
break;
} else {
/*
* Our initial offset might be in the middle of an
* item. Make sure it all makes sense.
*/
if (key.offset > offset)
break;
if (item_end <= offset)
break;
}
/* desc = NULL to just sum all the item lengths */
if (!dest)
copy_end = item_end;
else
copy_end = min(offset + len, item_end);
/* Number of bytes in this item we want to copy */
copy_bytes = copy_end - offset;
/* Offset from the start of item for copying */
copy_offset = offset - key.offset;
if (dest) {
if (dest_page)
kaddr = kmap_local_page(dest_page);
data = btrfs_item_ptr(leaf, path->slots[0], void);
read_extent_buffer(leaf, kaddr + dest_offset,
(unsigned long)data + copy_offset,
copy_bytes);
if (dest_page)
kunmap_local(kaddr);
}
offset += copy_bytes;
dest_offset += copy_bytes;
len -= copy_bytes;
copied += copy_bytes;
path->slots[0]++;
if (path->slots[0] >= btrfs_header_nritems(path->nodes[0])) {
/*
* We've reached the last slot in this leaf and we need
* to go to the next leaf.
*/
ret = btrfs_next_leaf(root, path);
if (ret < 0) {
break;
} else if (ret > 0) {
ret = 0;
break;
}
}
}
out:
btrfs_free_path(path);
if (!ret)
ret = copied;
return ret;
}
/*
* Delete an fsverity orphan
*
* @trans: transaction to do the delete in
* @inode: inode to orphan
*
* Capture verity orphan specific logic that is repeated in the couple places
* we delete verity orphans. Specifically, handling ENOENT and ignoring inodes
* with 0 links.
*
* Returns zero on success or a negative error code on failure.
*/
static int del_orphan(struct btrfs_trans_handle *trans, struct btrfs_inode *inode)
{
struct btrfs_root *root = inode->root;
int ret;
/*
* If the inode has no links, it is either already unlinked, or was
* created with O_TMPFILE. In either case, it should have an orphan from
* that other operation. Rather than reference count the orphans, we
* simply ignore them here, because we only invoke the verity path in
* the orphan logic when i_nlink is 1.
*/
if (!inode->vfs_inode.i_nlink)
return 0;
ret = btrfs_del_orphan_item(trans, root, btrfs_ino(inode));
if (ret == -ENOENT)
ret = 0;
return ret;
}
/*
* Rollback in-progress verity if we encounter an error.
*
* @inode: inode verity had an error for
*
* We try to handle recoverable errors while enabling verity by rolling it back
* and just failing the operation, rather than having an fs level error no
* matter what. However, any error in rollback is unrecoverable.
*
* Returns 0 on success, negative error code on failure.
*/
static int rollback_verity(struct btrfs_inode *inode)
{
struct btrfs_trans_handle *trans = NULL;
struct btrfs_root *root = inode->root;
int ret;
ASSERT(inode_is_locked(&inode->vfs_inode));
truncate_inode_pages(inode->vfs_inode.i_mapping, inode->vfs_inode.i_size);
clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &inode->runtime_flags);
ret = btrfs_drop_verity_items(inode);
if (ret) {
btrfs_handle_fs_error(root->fs_info, ret,
"failed to drop verity items in rollback %llu",
(u64)inode->vfs_inode.i_ino);
goto out;
}
/*
* 1 for updating the inode flag
* 1 for deleting the orphan
*/
trans = btrfs_start_transaction(root, 2);
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
trans = NULL;
btrfs_handle_fs_error(root->fs_info, ret,
"failed to start transaction in verity rollback %llu",
(u64)inode->vfs_inode.i_ino);
goto out;
}
inode->ro_flags &= ~BTRFS_INODE_RO_VERITY;
btrfs_sync_inode_flags_to_i_flags(&inode->vfs_inode);
ret = btrfs_update_inode(trans, root, inode);
if (ret) {
btrfs_abort_transaction(trans, ret);
goto out;
}
ret = del_orphan(trans, inode);
if (ret) {
btrfs_abort_transaction(trans, ret);
goto out;
}
out:
if (trans)
btrfs_end_transaction(trans);
return ret;
}
/*
* Finalize making the file a valid verity file
*
* @inode: inode to be marked as verity
* @desc: contents of the verity descriptor to write (not NULL)
* @desc_size: size of the verity descriptor
*
* Do the actual work of finalizing verity after successfully writing the Merkle
* tree:
*
* - write out the descriptor items
* - mark the inode with the verity flag
* - delete the orphan item
* - mark the ro compat bit
* - clear the in progress bit
*
* Returns 0 on success, negative error code on failure.
*/
static int finish_verity(struct btrfs_inode *inode, const void *desc,
size_t desc_size)
{
struct btrfs_trans_handle *trans = NULL;
struct btrfs_root *root = inode->root;
struct btrfs_verity_descriptor_item item;
int ret;
/* Write out the descriptor item */
memset(&item, 0, sizeof(item));
btrfs_set_stack_verity_descriptor_size(&item, desc_size);
ret = write_key_bytes(inode, BTRFS_VERITY_DESC_ITEM_KEY, 0,
(const char *)&item, sizeof(item));
if (ret)
goto out;
/* Write out the descriptor itself */
ret = write_key_bytes(inode, BTRFS_VERITY_DESC_ITEM_KEY, 1,
desc, desc_size);
if (ret)
goto out;
/*
* 1 for updating the inode flag
* 1 for deleting the orphan
*/
trans = btrfs_start_transaction(root, 2);
if (IS_ERR(trans)) {
ret = PTR_ERR(trans);
goto out;
}
inode->ro_flags |= BTRFS_INODE_RO_VERITY;
btrfs_sync_inode_flags_to_i_flags(&inode->vfs_inode);
ret = btrfs_update_inode(trans, root, inode);
if (ret)
goto end_trans;
ret = del_orphan(trans, inode);
if (ret)
goto end_trans;
clear_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &inode->runtime_flags);
btrfs_set_fs_compat_ro(root->fs_info, VERITY);
end_trans:
btrfs_end_transaction(trans);
out:
return ret;
}
/*
* fsverity op that begins enabling verity.
*
* @filp: file to enable verity on
*
* Begin enabling fsverity for the file. We drop any existing verity items, add
* an orphan and set the in progress bit.
*
* Returns 0 on success, negative error code on failure.
*/
static int btrfs_begin_enable_verity(struct file *filp)
{
struct btrfs_inode *inode = BTRFS_I(file_inode(filp));
struct btrfs_root *root = inode->root;
struct btrfs_trans_handle *trans;
int ret;
ASSERT(inode_is_locked(file_inode(filp)));
if (test_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &inode->runtime_flags))
return -EBUSY;
/*
* This should almost never do anything, but theoretically, it's
* possible that we failed to enable verity on a file, then were
* interrupted or failed while rolling back, failed to cleanup the
* orphan, and finally attempt to enable verity again.
*/
ret = btrfs_drop_verity_items(inode);
if (ret)
return ret;
/* 1 for the orphan item */
trans = btrfs_start_transaction(root, 1);
if (IS_ERR(trans))
return PTR_ERR(trans);
ret = btrfs_orphan_add(trans, inode);
if (!ret)
set_bit(BTRFS_INODE_VERITY_IN_PROGRESS, &inode->runtime_flags);
btrfs_end_transaction(trans);
return 0;
}
/*
* fsverity op that ends enabling verity.
*
* @filp: file we are finishing enabling verity on
* @desc: verity descriptor to write out (NULL in error conditions)
* @desc_size: size of the verity descriptor (variable with signatures)
* @merkle_tree_size: size of the merkle tree in bytes
*
* If desc is null, then VFS is signaling an error occurred during verity
* enable, and we should try to rollback. Otherwise, attempt to finish verity.
*
* Returns 0 on success, negative error code on error.
*/
static int btrfs_end_enable_verity(struct file *filp, const void *desc,
size_t desc_size, u64 merkle_tree_size)
{
struct btrfs_inode *inode = BTRFS_I(file_inode(filp));
int ret = 0;
int rollback_ret;
ASSERT(inode_is_locked(file_inode(filp)));
if (desc == NULL)
goto rollback;
ret = finish_verity(inode, desc, desc_size);
if (ret)
goto rollback;
return ret;
rollback:
rollback_ret = rollback_verity(inode);
if (rollback_ret)
btrfs_err(inode->root->fs_info,
"failed to rollback verity items: %d", rollback_ret);
return ret;
}
/*
* fsverity op that gets the struct fsverity_descriptor.
*
* @inode: inode to get the descriptor of
* @buf: output buffer for the descriptor contents
* @buf_size: size of the output buffer. 0 to query the size
*
* fsverity does a two pass setup for reading the descriptor, in the first pass
* it calls with buf_size = 0 to query the size of the descriptor, and then in
* the second pass it actually reads the descriptor off disk.
*
* Returns the size on success or a negative error code on failure.
*/
int btrfs_get_verity_descriptor(struct inode *inode, void *buf, size_t buf_size)
{
u64 true_size;
int ret = 0;
struct btrfs_verity_descriptor_item item;
memset(&item, 0, sizeof(item));
ret = read_key_bytes(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY, 0,
(char *)&item, sizeof(item), NULL);
if (ret < 0)
return ret;
if (item.reserved[0] != 0 || item.reserved[1] != 0)
return -EUCLEAN;
true_size = btrfs_stack_verity_descriptor_size(&item);
if (true_size > INT_MAX)
return -EUCLEAN;
if (buf_size == 0)
return true_size;
if (buf_size < true_size)
return -ERANGE;
ret = read_key_bytes(BTRFS_I(inode), BTRFS_VERITY_DESC_ITEM_KEY, 1,
buf, buf_size, NULL);
if (ret < 0)
return ret;
if (ret != true_size)
return -EIO;
return true_size;
}
/*
* fsverity op that reads and caches a merkle tree page.
*
* @inode: inode to read a merkle tree page for
* @index: page index relative to the start of the merkle tree
* @num_ra_pages: number of pages to readahead. Optional, we ignore it
*
* The Merkle tree is stored in the filesystem btree, but its pages are cached
* with a logical position past EOF in the inode's mapping.
*
* Returns the page we read, or an ERR_PTR on error.
*/
static struct page *btrfs_read_merkle_tree_page(struct inode *inode,
pgoff_t index,
unsigned long num_ra_pages)
{
struct page *page;
u64 off = (u64)index << PAGE_SHIFT;
loff_t merkle_pos = merkle_file_pos(inode);
int ret;
if (merkle_pos < 0)
return ERR_PTR(merkle_pos);
if (merkle_pos > inode->i_sb->s_maxbytes - off - PAGE_SIZE)
return ERR_PTR(-EFBIG);
index += merkle_pos >> PAGE_SHIFT;
again:
page = find_get_page_flags(inode->i_mapping, index, FGP_ACCESSED);
if (page) {
if (PageUptodate(page))
return page;
lock_page(page);
/*
* We only insert uptodate pages, so !Uptodate has to be
* an error
*/
if (!PageUptodate(page)) {
unlock_page(page);
put_page(page);
return ERR_PTR(-EIO);
}
unlock_page(page);
return page;
}
page = __page_cache_alloc(mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS));
if (!page)
return ERR_PTR(-ENOMEM);
/*
* Merkle item keys are indexed from byte 0 in the merkle tree.
* They have the form:
*
* [ inode objectid, BTRFS_MERKLE_ITEM_KEY, offset in bytes ]
*/
ret = read_key_bytes(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY, off,
page_address(page), PAGE_SIZE, page);
if (ret < 0) {
put_page(page);
return ERR_PTR(ret);
}
if (ret < PAGE_SIZE)
memzero_page(page, ret, PAGE_SIZE - ret);
SetPageUptodate(page);
ret = add_to_page_cache_lru(page, inode->i_mapping, index, GFP_NOFS);
if (!ret) {
/* Inserted and ready for fsverity */
unlock_page(page);
} else {
put_page(page);
/* Did someone race us into inserting this page? */
if (ret == -EEXIST)
goto again;
page = ERR_PTR(ret);
}
return page;
}
/*
* fsverity op that writes a Merkle tree block into the btree.
*
* @inode: inode to write a Merkle tree block for
* @buf: Merkle tree data block to write
* @index: index of the block in the Merkle tree
* @log_blocksize: log base 2 of the Merkle tree block size
*
* Note that the block size could be different from the page size, so it is not
* safe to assume that index is a page index.
*
* Returns 0 on success or negative error code on failure
*/
static int btrfs_write_merkle_tree_block(struct inode *inode, const void *buf,
u64 index, int log_blocksize)
{
u64 off = index << log_blocksize;
u64 len = 1ULL << log_blocksize;
loff_t merkle_pos = merkle_file_pos(inode);
if (merkle_pos < 0)
return merkle_pos;
if (merkle_pos > inode->i_sb->s_maxbytes - off - len)
return -EFBIG;
return write_key_bytes(BTRFS_I(inode), BTRFS_VERITY_MERKLE_ITEM_KEY,
off, buf, len);
}
const struct fsverity_operations btrfs_verityops = {
.begin_enable_verity = btrfs_begin_enable_verity,
.end_enable_verity = btrfs_end_enable_verity,
.get_verity_descriptor = btrfs_get_verity_descriptor,
.read_merkle_tree_page = btrfs_read_merkle_tree_page,
.write_merkle_tree_block = btrfs_write_merkle_tree_block,
};