cbfs_private.c

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/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0-or-later */
 
#include <commonlib/bsd/cbfs_private.h>
#include <assert.h>
 
static enum cb_err read_next_header(cbfs_dev_t dev, size_t *offset, struct cbfs_file *buffer,
                                    const size_t devsize)
{
        DEBUG("Looking for next file @%#zx...\n", *offset);
        *offset = ALIGN_UP(*offset, CBFS_ALIGNMENT);
        while (*offset + sizeof(*buffer) < devsize) {
                if (cbfs_dev_read(dev, buffer, *offset, sizeof(*buffer)) != sizeof(*buffer))
                        return CB_CBFS_IO;
 
                if (memcmp(buffer->magic, CBFS_FILE_MAGIC, sizeof(buffer->magic)) == 0)
                        return CB_SUCCESS;
 
                *offset += CBFS_ALIGNMENT;
        }
 
        DEBUG("End of CBFS reached\n");
        return CB_CBFS_NOT_FOUND;
}
 
enum cb_err cbfs_walk(cbfs_dev_t dev, enum cb_err (*walker)(cbfs_dev_t dev, size_t offset,
                                                            const union cbfs_mdata *mdata,
                                                            size_t already_read, void *arg),
                      void *arg, struct vb2_hash *metadata_hash, enum cbfs_walk_flags flags)
{
        const bool do_hash = CBFS_ENABLE_HASHING && metadata_hash;
        const size_t devsize = cbfs_dev_size(dev);
        struct vb2_digest_context dc;
        vb2_error_t vbrv;
 
        assert(CBFS_ENABLE_HASHING || (!metadata_hash && !(flags & CBFS_WALK_WRITEBACK_HASH)));
        if (do_hash && (vbrv = vb2_digest_init(&dc, metadata_hash->algo))) {
                ERROR("Metadata hash digest (%d) init error: %#x\n", metadata_hash->algo, vbrv);
                return CB_ERR_ARG;
        }
 
        size_t offset = 0;
        enum cb_err ret_header;
        enum cb_err ret_walker = CB_CBFS_NOT_FOUND;
        union cbfs_mdata mdata;
        while ((ret_header = read_next_header(dev, &offset, &mdata.h, devsize)) == CB_SUCCESS) {
                const uint32_t attr_offset = be32toh(mdata.h.attributes_offset);
                const uint32_t data_offset = be32toh(mdata.h.offset);
                const uint32_t data_length = be32toh(mdata.h.len);
                const uint32_t type = be32toh(mdata.h.type);
                const bool empty = (type == CBFS_TYPE_DELETED || type == CBFS_TYPE_NULL);
 
                DEBUG("Found CBFS header @%#zx (type %d, attr +%#x, data +%#x, length %#x)\n",
                      offset, type, attr_offset, data_offset, data_length);
                if (data_offset > sizeof(mdata) || data_length > devsize ||
                    offset + data_offset + data_length > devsize) {
                        ERROR("File @%#zx too large\n", offset);
                        offset += CBFS_ALIGNMENT;
                        continue;
                }
 
                if (empty && !(flags & CBFS_WALK_INCLUDE_EMPTY))
                        goto next_file;
 
                /* When hashing we need to read everything. Otherwise skip the attributes.
                   attr_offset may be 0, which means there are no attributes. */
                ssize_t todo;
                if (do_hash || attr_offset == 0)
                        todo = data_offset - sizeof(mdata.h);
                else
                        todo = attr_offset - sizeof(mdata.h);
                if (todo <= 0 || data_offset < attr_offset) {
                        ERROR("Corrupt file header @%#zx\n", offset);
                        goto next_file;
                }
 
                /* Read the rest of the metadata (filename, and possibly attributes). */
                assert(todo > 0 && todo <= sizeof(mdata) - sizeof(mdata.h));
                if (cbfs_dev_read(dev, mdata.raw + sizeof(mdata.h),
                                  offset + sizeof(mdata.h), todo) != todo)
                        return CB_CBFS_IO;
                /* Force filename null-termination, just in case. */
                mdata.raw[attr_offset ? attr_offset - 1 : data_offset - 1] = '\0';
                DEBUG("File name: '%s'\n", mdata.h.filename);
 
                if (do_hash && !empty && vb2_digest_extend(&dc, mdata.raw, data_offset))
                        return CB_ERR;
 
                if (walker && ret_walker == CB_CBFS_NOT_FOUND)
                        ret_walker = walker(dev, offset, &mdata, sizeof(mdata.h) + todo, arg);
 
                /* Return IO errors immediately. For others, finish the hash first if needed. */
                if (ret_walker == CB_CBFS_IO || (ret_walker != CB_CBFS_NOT_FOUND && !do_hash))
                        return ret_walker;
 
next_file:
                offset += data_offset + data_length;
        }
 
        if (ret_header != CB_CBFS_NOT_FOUND)
                return ret_header;
 
        if (do_hash) {
                uint8_t real_hash[VB2_MAX_DIGEST_SIZE];
                size_t hash_size = vb2_digest_size(metadata_hash->algo);
                if (vb2_digest_finalize(&dc, real_hash, hash_size))
                        return CB_ERR;
                if (flags & CBFS_WALK_WRITEBACK_HASH)
                        memcpy(metadata_hash->raw, real_hash, hash_size);
                else if (memcmp(metadata_hash->raw, real_hash, hash_size) != 0)
                        return CB_CBFS_HASH_MISMATCH;
        }
 
        return ret_walker;
}
 
enum cb_err cbfs_copy_fill_metadata(union cbfs_mdata *dst, const union cbfs_mdata *src,
                                    size_t already_read, cbfs_dev_t dev, size_t offset)
{
        /* First, copy the stuff that cbfs_walk() already read for us. */
        memcpy(dst, src, already_read);
 
        /* Then read in whatever metadata may be left (will only happen in non-hashing case). */
        const size_t todo = be32toh(src->h.offset) - already_read;
        assert(todo <= sizeof(*dst) - already_read);
        if (todo && cbfs_dev_read(dev, dst->raw + already_read, offset + already_read,
                                  todo) != todo)
                return CB_CBFS_IO;
        return CB_SUCCESS;
}
 
struct cbfs_lookup_args {
        union cbfs_mdata *mdata_out;
        const char *name;
        size_t namesize;
        size_t *data_offset_out;
};
 
static enum cb_err lookup_walker(cbfs_dev_t dev, size_t offset, const union cbfs_mdata *mdata,
                                 size_t already_read, void *arg)
{
        struct cbfs_lookup_args *args = arg;
        /* Check if the name we're looking for could fit, then we can safely memcmp() it. */
        if (args->namesize > already_read - offsetof(union cbfs_mdata, h.filename) ||
            memcmp(args->name, mdata->h.filename, args->namesize) != 0)
                return CB_CBFS_NOT_FOUND;
 
        LOG("Found '%s' @%#zx size %#x\n", args->name, offset, be32toh(mdata->h.len));
        if (cbfs_copy_fill_metadata(args->mdata_out, mdata, already_read, dev, offset))
                return CB_CBFS_IO;
 
        *args->data_offset_out = offset + be32toh(mdata->h.offset);
        return CB_SUCCESS;
}
 
enum cb_err cbfs_lookup(cbfs_dev_t dev, const char *name, union cbfs_mdata *mdata_out,
                        size_t *data_offset_out, struct vb2_hash *metadata_hash)
{
        struct cbfs_lookup_args args = {
                .mdata_out = mdata_out,
                .name = name,
                .namesize = strlen(name) + 1,   /* Count trailing \0 so we can memcmp() it. */
                .data_offset_out = data_offset_out,
        };
        return cbfs_walk(dev, lookup_walker, &args, metadata_hash, 0);
}
 
const void *cbfs_find_attr(const union cbfs_mdata *mdata, uint32_t attr_tag, size_t size_check)
{
        uint32_t offset = be32toh(mdata->h.attributes_offset);
        uint32_t end = be32toh(mdata->h.offset);
 
        if (!offset)
                return NULL;
 
        while (offset + sizeof(struct cbfs_file_attribute) <= end) {
                const struct cbfs_file_attribute *attr = (const void *)mdata->raw + offset;
                const uint32_t tag = be32toh(attr->tag);
                const uint32_t len = be32toh(attr->len);
 
                if (len < sizeof(struct cbfs_file_attribute) || len > end - offset) {
                        ERROR("Attribute %s[%x] invalid length: %u\n",
                              mdata->h.filename, tag, len);
                        return NULL;
                }
                if (tag == attr_tag) {
                        if (size_check && len != size_check) {
                                ERROR("Attribute %s[%x] size mismatch: %u != %zu\n",
                                      mdata->h.filename, tag, len, size_check);
                                return NULL;
                        }
                        return attr;
                }
                offset += len;
        }
 
        return NULL;
}
 
const struct vb2_hash *cbfs_file_hash(const union cbfs_mdata *mdata)
{
        /* Hashes are variable-length attributes, so need to manually check the length. */
        const struct cbfs_file_attr_hash *attr =
                cbfs_find_attr(mdata, CBFS_FILE_ATTR_TAG_HASH, 0);
        if (!attr)
                return NULL;    /* no hash */
        const size_t asize = be32toh(attr->len);
 
        const struct vb2_hash *hash = &attr->hash;
        const size_t hsize = vb2_digest_size(hash->algo);
        if (!hsize) {
                ERROR("Hash algo %u for '%s' unsupported.\n", hash->algo, mdata->h.filename);
                return NULL;
        }
        if (hsize != asize - offsetof(struct cbfs_file_attr_hash, hash.raw)) {
                ERROR("Hash attribute size for '%s' (%zu) incorrect for algo %u.\n",
                      mdata->h.filename, asize, hash->algo);
                return NULL;
        }
        return hash;
}