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Diffstat (limited to '')
| -rw-r--r-- | fuse_sideload.c | 503 |
1 files changed, 503 insertions, 0 deletions
diff --git a/fuse_sideload.c b/fuse_sideload.c new file mode 100644 index 000000000..ab91defbf --- /dev/null +++ b/fuse_sideload.c @@ -0,0 +1,503 @@ +/* + * Copyright (C) 2014 The Android Open Source Project + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +// This module creates a special filesystem containing two files. +// +// "/sideload/package.zip" appears to be a normal file, but reading +// from it causes data to be fetched from the adb host. We can use +// this to sideload packages over an adb connection without having to +// store the entire package in RAM on the device. +// +// Because we may not trust the adb host, this filesystem maintains +// the following invariant: each read of a given position returns the +// same data as the first read at that position. That is, once a +// section of the file is read, future reads of that section return +// the same data. (Otherwise, a malicious adb host process could +// return one set of bits when the package is read for signature +// verification, and then different bits for when the package is +// accessed by the installer.) If the adb host returns something +// different than it did on the first read, the reader of the file +// will see their read fail with EINVAL. +// +// The other file, "/sideload/exit", is used to control the subprocess +// that creates this filesystem. Calling stat() on the exit file +// causes the filesystem to be unmounted and the adb process on the +// device shut down. +// +// Note that only the minimal set of file operations needed for these +// two files is implemented. In particular, you can't opendir() or +// readdir() on the "/sideload" directory; ls on it won't work. + +#include <ctype.h> +#include <dirent.h> +#include <errno.h> +#include <fcntl.h> +#include <limits.h> +#include <linux/fuse.h> +#include <pthread.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <sys/inotify.h> +#include <sys/mount.h> +#include <sys/resource.h> +#include <sys/stat.h> +#include <sys/statfs.h> +#include <sys/time.h> +#include <sys/uio.h> +#include <unistd.h> + +#include "mincrypt/sha256.h" +#include "fuse_sideload.h" + +#define PACKAGE_FILE_ID (FUSE_ROOT_ID+1) +#define EXIT_FLAG_ID (FUSE_ROOT_ID+2) + +#define NO_STATUS 1 +#define NO_STATUS_EXIT 2 + +struct fuse_data { + int ffd; // file descriptor for the fuse socket + + struct provider_vtab* vtab; + void* cookie; + + uint64_t file_size; // bytes + + uint32_t block_size; // block size that the adb host is using to send the file to us + uint32_t file_blocks; // file size in block_size blocks + + uid_t uid; + gid_t gid; + + uint32_t curr_block; // cache the block most recently read from the host + uint8_t* block_data; + + uint8_t* extra_block; // another block of storage for reads that + // span two blocks + + uint8_t* hashes; // SHA-256 hash of each block (all zeros + // if block hasn't been read yet) +}; + +static void fuse_reply(struct fuse_data* fd, __u64 unique, const void *data, size_t len) +{ + struct fuse_out_header hdr; + struct iovec vec[2]; + int res; + + hdr.len = len + sizeof(hdr); + hdr.error = 0; + hdr.unique = unique; + + vec[0].iov_base = &hdr; + vec[0].iov_len = sizeof(hdr); + vec[1].iov_base = data; + vec[1].iov_len = len; + + res = writev(fd->ffd, vec, 2); + if (res < 0) { + printf("*** REPLY FAILED *** %d\n", errno); + } +} + +static int handle_init(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) { + const struct fuse_init_in* req = data; + struct fuse_init_out out; + + out.major = FUSE_KERNEL_VERSION; + out.minor = FUSE_KERNEL_MINOR_VERSION; + out.max_readahead = req->max_readahead; + out.flags = 0; + out.max_background = 32; + out.congestion_threshold = 32; + out.max_write = 4096; + fuse_reply(fd, hdr->unique, &out, sizeof(out)); + + return NO_STATUS; +} + +static void fill_attr(struct fuse_attr* attr, struct fuse_data* fd, + uint64_t nodeid, uint64_t size, uint32_t mode) { + memset(attr, 0, sizeof(*attr)); + attr->nlink = 1; + attr->uid = fd->uid; + attr->gid = fd->gid; + attr->blksize = 4096; + + attr->ino = nodeid; + attr->size = size; + attr->blocks = (size == 0) ? 0 : (((size-1) / attr->blksize) + 1); + attr->mode = mode; +} + +static int handle_getattr(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) { + const struct fuse_getattr_in* req = data; + struct fuse_attr_out out; + memset(&out, 0, sizeof(out)); + out.attr_valid = 10; + + if (hdr->nodeid == FUSE_ROOT_ID) { + fill_attr(&(out.attr), fd, hdr->nodeid, 4096, S_IFDIR | 0555); + } else if (hdr->nodeid == PACKAGE_FILE_ID) { + fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444); + } else if (hdr->nodeid == EXIT_FLAG_ID) { + fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0); + } else { + return -ENOENT; + } + + fuse_reply(fd, hdr->unique, &out, sizeof(out)); + return (hdr->nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS; +} + +static int handle_lookup(void* data, struct fuse_data* fd, + const struct fuse_in_header* hdr) { + struct fuse_entry_out out; + memset(&out, 0, sizeof(out)); + out.entry_valid = 10; + out.attr_valid = 10; + + if (strncmp(FUSE_SIDELOAD_HOST_FILENAME, data, + sizeof(FUSE_SIDELOAD_HOST_FILENAME)) == 0) { + out.nodeid = PACKAGE_FILE_ID; + out.generation = PACKAGE_FILE_ID; + fill_attr(&(out.attr), fd, PACKAGE_FILE_ID, fd->file_size, S_IFREG | 0444); + } else if (strncmp(FUSE_SIDELOAD_HOST_EXIT_FLAG, data, + sizeof(FUSE_SIDELOAD_HOST_EXIT_FLAG)) == 0) { + out.nodeid = EXIT_FLAG_ID; + out.generation = EXIT_FLAG_ID; + fill_attr(&(out.attr), fd, EXIT_FLAG_ID, 0, S_IFREG | 0); + } else { + return -ENOENT; + } + + fuse_reply(fd, hdr->unique, &out, sizeof(out)); + return (out.nodeid == EXIT_FLAG_ID) ? NO_STATUS_EXIT : NO_STATUS; +} + +static int handle_open(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) { + const struct fuse_open_in* req = data; + + if (hdr->nodeid == EXIT_FLAG_ID) return -EPERM; + if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT; + + struct fuse_open_out out; + memset(&out, 0, sizeof(out)); + out.fh = 10; // an arbitrary number; we always use the same handle + fuse_reply(fd, hdr->unique, &out, sizeof(out)); + return NO_STATUS; +} + +static int handle_flush(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) { + return 0; +} + +static int handle_release(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) { + return 0; +} + +// Fetch a block from the host into fd->curr_block and fd->block_data. +// Returns 0 on successful fetch, negative otherwise. +static int fetch_block(struct fuse_data* fd, uint32_t block) { + if (block == fd->curr_block) { + return 0; + } + + if (block >= fd->file_blocks) { + memset(fd->block_data, 0, fd->block_size); + fd->curr_block = block; + return 0; + } + + size_t fetch_size = fd->block_size; + if (block * fd->block_size + fetch_size > fd->file_size) { + // If we're reading the last (partial) block of the file, + // expect a shorter response from the host, and pad the rest + // of the block with zeroes. + fetch_size = fd->file_size - (block * fd->block_size); + memset(fd->block_data + fetch_size, 0, fd->block_size - fetch_size); + } + + int result = fd->vtab->read_block(fd->cookie, block, fd->block_data, fetch_size); + if (result < 0) return result; + + fd->curr_block = block; + + // Verify the hash of the block we just got from the host. + // + // - If the hash of the just-received data matches the stored hash + // for the block, accept it. + // - If the stored hash is all zeroes, store the new hash and + // accept the block (this is the first time we've read this + // block). + // - Otherwise, return -EINVAL for the read. + + uint8_t hash[SHA256_DIGEST_SIZE]; + SHA256_hash(fd->block_data, fd->block_size, hash); + uint8_t* blockhash = fd->hashes + block * SHA256_DIGEST_SIZE; + if (memcmp(hash, blockhash, SHA256_DIGEST_SIZE) == 0) { + return 0; + } + + int i; + for (i = 0; i < SHA256_DIGEST_SIZE; ++i) { + if (blockhash[i] != 0) { + fd->curr_block = -1; + return -EIO; + } + } + + memcpy(blockhash, hash, SHA256_DIGEST_SIZE); + return 0; +} + +static int handle_read(void* data, struct fuse_data* fd, const struct fuse_in_header* hdr) { + const struct fuse_read_in* req = data; + struct fuse_out_header outhdr; + struct iovec vec[3]; + int vec_used; + int result; + + if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT; + + uint64_t offset = req->offset; + uint32_t size = req->size; + + // The docs on the fuse kernel interface are vague about what to + // do when a read request extends past the end of the file. We + // can return a short read -- the return structure does include a + // length field -- but in testing that caused the program using + // the file to segfault. (I speculate that this is due to the + // reading program accessing it via mmap; maybe mmap dislikes when + // you return something short of a whole page?) To fix this we + // zero-pad reads that extend past the end of the file so we're + // always returning exactly as many bytes as were requested. + // (Users of the mapped file have to know its real length anyway.) + + outhdr.len = sizeof(outhdr) + size; + outhdr.error = 0; + outhdr.unique = hdr->unique; + vec[0].iov_base = &outhdr; + vec[0].iov_len = sizeof(outhdr); + + uint32_t block = offset / fd->block_size; + result = fetch_block(fd, block); + if (result != 0) return result; + + // Two cases: + // + // - the read request is entirely within this block. In this + // case we can reply immediately. + // + // - the read request goes over into the next block. Note that + // since we mount the filesystem with max_read=block_size, a + // read can never span more than two blocks. In this case we + // copy the block to extra_block and issue a fetch for the + // following block. + + uint32_t block_offset = offset - (block * fd->block_size); + + if (size + block_offset <= fd->block_size) { + // First case: the read fits entirely in the first block. + + vec[1].iov_base = fd->block_data + block_offset; + vec[1].iov_len = size; + vec_used = 2; + } else { + // Second case: the read spills over into the next block. + + memcpy(fd->extra_block, fd->block_data + block_offset, + fd->block_size - block_offset); + vec[1].iov_base = fd->extra_block; + vec[1].iov_len = fd->block_size - block_offset; + + result = fetch_block(fd, block+1); + if (result != 0) return result; + vec[2].iov_base = fd->block_data; + vec[2].iov_len = size - vec[1].iov_len; + vec_used = 3; + } + + if (writev(fd->ffd, vec, vec_used) < 0) { + printf("*** READ REPLY FAILED: %s ***\n", strerror(errno)); + } + return NO_STATUS; +} + +int run_fuse_sideload(struct provider_vtab* vtab, void* cookie, + uint64_t file_size, uint32_t block_size) +{ + int result; + + // If something's already mounted on our mountpoint, try to remove + // it. (Mostly in case of a previous abnormal exit.) + umount2(FUSE_SIDELOAD_HOST_MOUNTPOINT, MNT_FORCE); + + if (block_size < 1024) { + fprintf(stderr, "block size (%u) is too small\n", block_size); + return -1; + } + if (block_size > (1<<22)) { // 4 MiB + fprintf(stderr, "block size (%u) is too large\n", block_size); + return -1; + } + + struct fuse_data fd; + memset(&fd, 0, sizeof(fd)); + fd.vtab = vtab; + fd.cookie = cookie; + fd.file_size = file_size; + fd.block_size = block_size; + fd.file_blocks = (file_size == 0) ? 0 : (((file_size-1) / block_size) + 1); + + if (fd.file_blocks > (1<<18)) { + fprintf(stderr, "file has too many blocks (%u)\n", fd.file_blocks); + result = -1; + goto done; + } + + fd.hashes = (uint8_t*)calloc(fd.file_blocks, SHA256_DIGEST_SIZE); + if (fd.hashes == NULL) { + fprintf(stderr, "failed to allocate %d bites for hashes\n", + fd.file_blocks * SHA256_DIGEST_SIZE); + result = -1; + goto done; + } + + fd.uid = getuid(); + fd.gid = getgid(); + + fd.curr_block = -1; + fd.block_data = (uint8_t*)malloc(block_size); + if (fd.block_data == NULL) { + fprintf(stderr, "failed to allocate %d bites for block_data\n", block_size); + result = -1; + goto done; + } + fd.extra_block = (uint8_t*)malloc(block_size); + if (fd.extra_block == NULL) { + fprintf(stderr, "failed to allocate %d bites for extra_block\n", block_size); + result = -1; + goto done; + } + + fd.ffd = open("/dev/fuse", O_RDWR); + if (fd.ffd < 0) { + perror("open /dev/fuse"); + result = -1; + goto done; + } + + char opts[256]; + snprintf(opts, sizeof(opts), + ("fd=%d,user_id=%d,group_id=%d,max_read=%zu," + "allow_other,rootmode=040000"), + fd.ffd, fd.uid, fd.gid, block_size); + + result = mount("/dev/fuse", FUSE_SIDELOAD_HOST_MOUNTPOINT, + "fuse", MS_NOSUID | MS_NODEV | MS_RDONLY | MS_NOEXEC, opts); + if (result < 0) { + perror("mount"); + goto done; + } + uint8_t request_buffer[sizeof(struct fuse_in_header) + PATH_MAX*8]; + for (;;) { + ssize_t len = read(fd.ffd, request_buffer, sizeof(request_buffer)); + if (len < 0) { + if (errno != EINTR) { + perror("read request"); + if (errno == ENODEV) { + result = -1; + break; + } + } + continue; + } + + if ((size_t)len < sizeof(struct fuse_in_header)) { + fprintf(stderr, "request too short: len=%zu\n", (size_t)len); + continue; + } + + struct fuse_in_header* hdr = (struct fuse_in_header*) request_buffer; + void* data = request_buffer + sizeof(struct fuse_in_header); + + result = -ENOSYS; + + switch (hdr->opcode) { + case FUSE_INIT: + result = handle_init(data, &fd, hdr); + break; + + case FUSE_LOOKUP: + result = handle_lookup(data, &fd, hdr); + break; + + case FUSE_GETATTR: + result = handle_getattr(data, &fd, hdr); + break; + + case FUSE_OPEN: + result = handle_open(data, &fd, hdr); + break; + + case FUSE_READ: + result = handle_read(data, &fd, hdr); + break; + + case FUSE_FLUSH: + result = handle_flush(data, &fd, hdr); + break; + + case FUSE_RELEASE: + result = handle_release(data, &fd, hdr); + break; + + default: + fprintf(stderr, "unknown fuse request opcode %d\n", hdr->opcode); + break; + } + + if (result == NO_STATUS_EXIT) { + result = 0; + break; + } + + if (result != NO_STATUS) { + struct fuse_out_header outhdr; + outhdr.len = sizeof(outhdr); + outhdr.error = result; + outhdr.unique = hdr->unique; + write(fd.ffd, &outhdr, sizeof(outhdr)); + } + } + + done: + fd.vtab->close(fd.cookie); + + result = umount2(FUSE_SIDELOAD_HOST_MOUNTPOINT, MNT_DETACH); + if (result < 0) { + printf("fuse_sideload umount failed: %s\n", strerror(errno)); + } + + if (fd.ffd) close(fd.ffd); + free(fd.hashes); + free(fd.block_data); + free(fd.extra_block); + + return result; +} |