1 files changed, 367 insertions, 0 deletions

diff --git a/fs/ext4/verity.c b/fs/ext4/verity.c
new file mode 100644
index 000000000000..d0d8a9795dd6
--- /dev/null
+++ b/fs/ext4/verity.c
@@ -0,0 +1,367 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/ext4/verity.c: fs-verity support for ext4
+ *
+ * Copyright 2019 Google LLC
+ */
+
+/*
+ * Implementation of fsverity_operations for ext4.
+ *
+ * ext4 stores the verity metadata (Merkle tree and fsverity_descriptor) past
+ * the end of the file, starting at the first 64K boundary beyond i_size.  This
+ * approach works because (a) verity files are readonly, and (b) pages fully
+ * beyond i_size aren't visible to userspace but can be read/written internally
+ * by ext4 with only some relatively small changes to ext4.  This approach
+ * avoids having to depend on the EA_INODE feature and on rearchitecturing
+ * ext4's xattr support to support paging multi-gigabyte xattrs into memory, and
+ * to support encrypting xattrs.  Note that the verity metadata *must* be
+ * encrypted when the file is, since it contains hashes of the plaintext data.
+ *
+ * Using a 64K boundary rather than a 4K one keeps things ready for
+ * architectures with 64K pages, and it doesn't necessarily waste space on-disk
+ * since there can be a hole between i_size and the start of the Merkle tree.
+ */
+
+#include <linux/quotaops.h>
+
+#include "ext4.h"
+#include "ext4_extents.h"
+#include "ext4_jbd2.h"
+
+static inline loff_t ext4_verity_metadata_pos(const struct inode *inode)
+{
+        return round_up(inode->i_size, 65536);
+}
+
+/*
+ * Read some verity metadata from the inode.  __vfs_read() can't be used because
+ * we need to read beyond i_size.
+ */
+static int pagecache_read(struct inode *inode, void *buf, size_t count,
+                          loff_t pos)
+{
+        while (count) {
+                size_t n = min_t(size_t, count,
+                                 PAGE_SIZE - offset_in_page(pos));
+                struct page *page;
+                void *addr;
+
+                page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
+                                         NULL);
+                if (IS_ERR(page))
+                        return PTR_ERR(page);
+
+                addr = kmap_atomic(page);
+                memcpy(buf, addr + offset_in_page(pos), n);
+                kunmap_atomic(addr);
+
+                put_page(page);
+
+                buf += n;
+                pos += n;
+                count -= n;
+        }
+        return 0;
+}
+
+/*
+ * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
+ * kernel_write() can't be used because the file descriptor is readonly.
+ */
+static int pagecache_write(struct inode *inode, const void *buf, size_t count,
+                           loff_t pos)
+{
+        if (pos + count > inode->i_sb->s_maxbytes)
+                return -EFBIG;
+
+        while (count) {
+                size_t n = min_t(size_t, count,
+                                 PAGE_SIZE - offset_in_page(pos));
+                struct page *page;
+                void *fsdata;
+                void *addr;
+                int res;
+
+                res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
+                                            &page, &fsdata);
+                if (res)
+                        return res;
+
+                addr = kmap_atomic(page);
+                memcpy(addr + offset_in_page(pos), buf, n);
+                kunmap_atomic(addr);
+
+                res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
+                                          page, fsdata);
+                if (res < 0)
+                        return res;
+                if (res != n)
+                        return -EIO;
+
+                buf += n;
+                pos += n;
+                count -= n;
+        }
+        return 0;
+}
+
+static int ext4_begin_enable_verity(struct file *filp)
+{
+        struct inode *inode = file_inode(filp);
+        const int credits = 2; /* superblock and inode for ext4_orphan_add() */
+        handle_t *handle;
+        int err;
+
+        if (ext4_verity_in_progress(inode))
+                return -EBUSY;
+
+        /*
+         * Since the file was opened readonly, we have to initialize the jbd
+         * inode and quotas here and not rely on ->open() doing it.  This must
+         * be done before evicting the inline data.
+         */
+
+        err = ext4_inode_attach_jinode(inode);
+        if (err)
+                return err;
+
+        err = dquot_initialize(inode);
+        if (err)
+                return err;
+
+        err = ext4_convert_inline_data(inode);
+        if (err)
+                return err;
+
+        if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
+                ext4_warning_inode(inode,
+                                   "verity is only allowed on extent-based files");
+                return -EOPNOTSUPP;
+        }
+
+        /*
+         * ext4 uses the last allocated block to find the verity descriptor, so
+         * we must remove any other blocks past EOF which might confuse things.
+         */
+        err = ext4_truncate(inode);
+        if (err)
+                return err;
+
+        handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
+        if (IS_ERR(handle))
+                return PTR_ERR(handle);
+
+        err = ext4_orphan_add(handle, inode);
+        if (err == 0)
+                ext4_set_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
+
+        ext4_journal_stop(handle);
+        return err;
+}
+
+/*
+ * ext4 stores the verity descriptor beginning on the next filesystem block
+ * boundary after the Merkle tree.  Then, the descriptor size is stored in the
+ * last 4 bytes of the last allocated filesystem block --- which is either the
+ * block in which the descriptor ends, or the next block after that if there
+ * weren't at least 4 bytes remaining.
+ *
+ * We can't simply store the descriptor in an xattr because it *must* be
+ * encrypted when ext4 encryption is used, but ext4 encryption doesn't encrypt
+ * xattrs.  Also, if the descriptor includes a large signature blob it may be
+ * too large to store in an xattr without the EA_INODE feature.
+ */
+static int ext4_write_verity_descriptor(struct inode *inode, const void *desc,
+                                        size_t desc_size, u64 merkle_tree_size)
+{
+        const u64 desc_pos = round_up(ext4_verity_metadata_pos(inode) +
+                                      merkle_tree_size, i_blocksize(inode));
+        const u64 desc_end = desc_pos + desc_size;
+        const __le32 desc_size_disk = cpu_to_le32(desc_size);
+        const u64 desc_size_pos = round_up(desc_end + sizeof(desc_size_disk),
+                                           i_blocksize(inode)) -
+                                  sizeof(desc_size_disk);
+        int err;
+
+        err = pagecache_write(inode, desc, desc_size, desc_pos);
+        if (err)
+                return err;
+
+        return pagecache_write(inode, &desc_size_disk, sizeof(desc_size_disk),
+                               desc_size_pos);
+}
+
+static int ext4_end_enable_verity(struct file *filp, const void *desc,
+                                  size_t desc_size, u64 merkle_tree_size)
+{
+        struct inode *inode = file_inode(filp);
+        const int credits = 2; /* superblock and inode for ext4_orphan_del() */
+        handle_t *handle;
+        int err = 0;
+        int err2;
+
+        if (desc != NULL) {
+                /* Succeeded; write the verity descriptor. */
+                err = ext4_write_verity_descriptor(inode, desc, desc_size,
+                                                   merkle_tree_size);
+
+                /* Write all pages before clearing VERITY_IN_PROGRESS. */
+                if (!err)
+                        err = filemap_write_and_wait(inode->i_mapping);
+        }
+
+        /* If we failed, truncate anything we wrote past i_size. */
+        if (desc == NULL || err)
+                ext4_truncate(inode);
+
+        /*
+         * We must always clean up by clearing EXT4_STATE_VERITY_IN_PROGRESS and
+         * deleting the inode from the orphan list, even if something failed.
+         * If everything succeeded, we'll also set the verity bit in the same
+         * transaction.
+         */
+
+        ext4_clear_inode_state(inode, EXT4_STATE_VERITY_IN_PROGRESS);
+
+        handle = ext4_journal_start(inode, EXT4_HT_INODE, credits);
+        if (IS_ERR(handle)) {
+                ext4_orphan_del(NULL, inode);
+                return PTR_ERR(handle);
+        }
+
+        err2 = ext4_orphan_del(handle, inode);
+        if (err2)
+                goto out_stop;
+
+        if (desc != NULL && !err) {
+                struct ext4_iloc iloc;
+
+                err = ext4_reserve_inode_write(handle, inode, &iloc);
+                if (err)
+                        goto out_stop;
+                ext4_set_inode_flag(inode, EXT4_INODE_VERITY);
+                ext4_set_inode_flags(inode);
+                err = ext4_mark_iloc_dirty(handle, inode, &iloc);
+        }
+out_stop:
+        ext4_journal_stop(handle);
+        return err ?: err2;
+}
+
+static int ext4_get_verity_descriptor_location(struct inode *inode,
+                                               size_t *desc_size_ret,
+                                               u64 *desc_pos_ret)
+{
+        struct ext4_ext_path *path;
+        struct ext4_extent *last_extent;
+        u32 end_lblk;
+        u64 desc_size_pos;
+        __le32 desc_size_disk;
+        u32 desc_size;
+        u64 desc_pos;
+        int err;
+
+        /*
+         * Descriptor size is in last 4 bytes of last allocated block.
+         * See ext4_write_verity_descriptor().
+         */
+
+        if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)) {
+                EXT4_ERROR_INODE(inode, "verity file doesn't use extents");
+                return -EFSCORRUPTED;
+        }
+
+        path = ext4_find_extent(inode, EXT_MAX_BLOCKS - 1, NULL, 0);
+        if (IS_ERR(path))
+                return PTR_ERR(path);
+
+        last_extent = path[path->p_depth].p_ext;
+        if (!last_extent) {
+                EXT4_ERROR_INODE(inode, "verity file has no extents");
+                ext4_ext_drop_refs(path);
+                kfree(path);
+                return -EFSCORRUPTED;
+        }
+
+        end_lblk = le32_to_cpu(last_extent->ee_block) +
+                   ext4_ext_get_actual_len(last_extent);
+        desc_size_pos = (u64)end_lblk << inode->i_blkbits;
+        ext4_ext_drop_refs(path);
+        kfree(path);
+
+        if (desc_size_pos < sizeof(desc_size_disk))
+                goto bad;
+        desc_size_pos -= sizeof(desc_size_disk);
+
+        err = pagecache_read(inode, &desc_size_disk, sizeof(desc_size_disk),
+                             desc_size_pos);
+        if (err)
+                return err;
+        desc_size = le32_to_cpu(desc_size_disk);
+
+        /*
+         * The descriptor is stored just before the desc_size_disk, but starting
+         * on a filesystem block boundary.
+         */
+
+        if (desc_size > INT_MAX || desc_size > desc_size_pos)
+                goto bad;
+
+        desc_pos = round_down(desc_size_pos - desc_size, i_blocksize(inode));
+        if (desc_pos < ext4_verity_metadata_pos(inode))
+                goto bad;
+
+        *desc_size_ret = desc_size;
+        *desc_pos_ret = desc_pos;
+        return 0;
+
+bad:
+        EXT4_ERROR_INODE(inode, "verity file corrupted; can't find descriptor");
+        return -EFSCORRUPTED;
+}
+
+static int ext4_get_verity_descriptor(struct inode *inode, void *buf,
+                                      size_t buf_size)
+{
+        size_t desc_size = 0;
+        u64 desc_pos = 0;
+        int err;
+
+        err = ext4_get_verity_descriptor_location(inode, &desc_size, &desc_pos);
+        if (err)
+                return err;
+
+        if (buf_size) {
+                if (desc_size > buf_size)
+                        return -ERANGE;
+                err = pagecache_read(inode, buf, desc_size, desc_pos);
+                if (err)
+                        return err;
+        }
+        return desc_size;
+}
+
+static struct page *ext4_read_merkle_tree_page(struct inode *inode,
+                                               pgoff_t index)
+{
+        index += ext4_verity_metadata_pos(inode) >> PAGE_SHIFT;
+
+        return read_mapping_page(inode->i_mapping, index, NULL);
+}
+
+static int ext4_write_merkle_tree_block(struct inode *inode, const void *buf,
+                                        u64 index, int log_blocksize)
+{
+        loff_t pos = ext4_verity_metadata_pos(inode) + (index << log_blocksize);
+
+        return pagecache_write(inode, buf, 1 << log_blocksize, pos);
+}
+
+const struct fsverity_operations ext4_verityops = {
+        .begin_enable_verity    = ext4_begin_enable_verity,
+        .end_enable_verity      = ext4_end_enable_verity,
+        .get_verity_descriptor  = ext4_get_verity_descriptor,
+        .read_merkle_tree_page  = ext4_read_merkle_tree_page,
+        .write_merkle_tree_block = ext4_write_merkle_tree_block,
+};