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-rw-r--r--fuse_sideload/fuse_sideload.cpp492
1 files changed, 492 insertions, 0 deletions
diff --git a/fuse_sideload/fuse_sideload.cpp b/fuse_sideload/fuse_sideload.cpp
new file mode 100644
index 000000000..1c7e98f01
--- /dev/null
+++ b/fuse_sideload/fuse_sideload.cpp
@@ -0,0 +1,492 @@
+/*
+ * 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 "fuse_sideload.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h> // PATH_MAX
+#include <linux/fuse.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/param.h> // MIN
+#include <sys/stat.h>
+#include <sys/uio.h>
+#include <unistd.h>
+
+#include <array>
+#include <string>
+#include <vector>
+
+#include <android-base/stringprintf.h>
+#include <android-base/unique_fd.h>
+#include <openssl/sha.h>
+
+static constexpr uint64_t PACKAGE_FILE_ID = FUSE_ROOT_ID + 1;
+static constexpr uint64_t EXIT_FLAG_ID = FUSE_ROOT_ID + 2;
+
+static constexpr int NO_STATUS = 1;
+static constexpr int NO_STATUS_EXIT = 2;
+
+using SHA256Digest = std::array<uint8_t, SHA256_DIGEST_LENGTH>;
+
+struct fuse_data {
+ android::base::unique_fd ffd; // file descriptor for the fuse socket
+
+ provider_vtab vtab;
+
+ 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
+
+ std::vector<SHA256Digest>
+ hashes; // SHA-256 hash of each block (all zeros if block hasn't been read yet)
+};
+
+static void fuse_reply(const fuse_data* fd, uint64_t unique, const void* data, size_t len) {
+ fuse_out_header hdr;
+ hdr.len = len + sizeof(hdr);
+ hdr.error = 0;
+ hdr.unique = unique;
+
+ struct iovec vec[2];
+ vec[0].iov_base = &hdr;
+ vec[0].iov_len = sizeof(hdr);
+ vec[1].iov_base = const_cast<void*>(data);
+ vec[1].iov_len = len;
+
+ int res = writev(fd->ffd, vec, 2);
+ if (res == -1) {
+ printf("*** REPLY FAILED *** %s\n", strerror(errno));
+ }
+}
+
+static int handle_init(void* data, fuse_data* fd, const fuse_in_header* hdr) {
+ const fuse_init_in* req = static_cast<const fuse_init_in*>(data);
+
+ // Kernel 2.6.16 is the first stable kernel with struct fuse_init_out defined (fuse version 7.6).
+ // The structure is the same from 7.6 through 7.22. Beginning with 7.23, the structure increased
+ // in size and added new parameters.
+ if (req->major != FUSE_KERNEL_VERSION || req->minor < 6) {
+ printf("Fuse kernel version mismatch: Kernel version %d.%d, Expected at least %d.6", req->major,
+ req->minor, FUSE_KERNEL_VERSION);
+ return -1;
+ }
+
+ fuse_init_out out;
+ out.minor = MIN(req->minor, FUSE_KERNEL_MINOR_VERSION);
+ size_t fuse_struct_size = sizeof(out);
+#if defined(FUSE_COMPAT_22_INIT_OUT_SIZE)
+ /* FUSE_KERNEL_VERSION >= 23. */
+
+ // If the kernel only works on minor revs older than or equal to 22, then use the older structure
+ // size since this code only uses the 7.22 version of the structure.
+ if (req->minor <= 22) {
+ fuse_struct_size = FUSE_COMPAT_22_INIT_OUT_SIZE;
+ }
+#endif
+
+ out.major = FUSE_KERNEL_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, fuse_struct_size);
+
+ return NO_STATUS;
+}
+
+static void fill_attr(fuse_attr* attr, const fuse_data* fd, uint64_t nodeid, uint64_t size,
+ uint32_t mode) {
+ *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 */, const fuse_data* fd, const fuse_in_header* hdr) {
+ fuse_attr_out 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, const fuse_data* fd, const fuse_in_header* hdr) {
+ if (data == nullptr) return -ENOENT;
+
+ fuse_entry_out out = {};
+ out.entry_valid = 10;
+ out.attr_valid = 10;
+
+ std::string filename(static_cast<const char*>(data));
+ if (filename == FUSE_SIDELOAD_HOST_FILENAME) {
+ 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 (filename == FUSE_SIDELOAD_HOST_EXIT_FLAG) {
+ 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 */, const fuse_data* fd, const fuse_in_header* hdr) {
+ if (hdr->nodeid == EXIT_FLAG_ID) return -EPERM;
+ if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
+
+ fuse_open_out 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 */, fuse_data* /* fd */, const fuse_in_header* /* hdr */) {
+ return 0;
+}
+
+static int handle_release(void* /* data */, fuse_data* /* fd */, const 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(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(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.
+
+ SHA256Digest hash;
+ SHA256(fd->block_data, fd->block_size, hash.data());
+
+ const SHA256Digest& blockhash = fd->hashes[block];
+ if (hash == blockhash) {
+ return 0;
+ }
+
+ for (uint8_t i : blockhash) {
+ if (i != 0) {
+ fd->curr_block = -1;
+ return -EIO;
+ }
+ }
+
+ fd->hashes[block] = hash;
+ return 0;
+}
+
+static int handle_read(void* data, fuse_data* fd, const fuse_in_header* hdr) {
+ if (hdr->nodeid != PACKAGE_FILE_ID) return -ENOENT;
+
+ const fuse_read_in* req = static_cast<const fuse_read_in*>(data);
+ 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.)
+
+ fuse_out_header outhdr;
+ outhdr.len = sizeof(outhdr) + size;
+ outhdr.error = 0;
+ outhdr.unique = hdr->unique;
+
+ struct iovec vec[3];
+ vec[0].iov_base = &outhdr;
+ vec[0].iov_len = sizeof(outhdr);
+
+ uint32_t block = offset / fd->block_size;
+ int 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);
+
+ int vec_used;
+ 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) == -1) {
+ printf("*** READ REPLY FAILED: %s ***\n", strerror(errno));
+ }
+ return NO_STATUS;
+}
+
+int run_fuse_sideload(const provider_vtab& vtab, uint64_t file_size, uint32_t block_size,
+ const char* mount_point) {
+ // If something's already mounted on our mountpoint, try to remove it. (Mostly in case of a
+ // previous abnormal exit.)
+ umount2(mount_point, MNT_FORCE);
+
+ // fs/fuse/inode.c in kernel code uses the greater of 4096 and the passed-in max_read.
+ if (block_size < 4096) {
+ 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;
+ }
+
+ fuse_data fd = {};
+ fd.vtab = vtab;
+ fd.file_size = file_size;
+ fd.block_size = block_size;
+ fd.file_blocks = (file_size == 0) ? 0 : (((file_size - 1) / block_size) + 1);
+
+ int result;
+ if (fd.file_blocks > (1 << 18)) {
+ fprintf(stderr, "file has too many blocks (%u)\n", fd.file_blocks);
+ result = -1;
+ goto done;
+ }
+
+ // All hashes will be zero-initialized.
+ fd.hashes.resize(fd.file_blocks);
+ fd.uid = getuid();
+ fd.gid = getgid();
+
+ fd.curr_block = -1;
+ fd.block_data = static_cast<uint8_t*>(malloc(block_size));
+ if (fd.block_data == nullptr) {
+ fprintf(stderr, "failed to allocate %d bites for block_data\n", block_size);
+ result = -1;
+ goto done;
+ }
+ fd.extra_block = static_cast<uint8_t*>(malloc(block_size));
+ if (fd.extra_block == nullptr) {
+ fprintf(stderr, "failed to allocate %d bites for extra_block\n", block_size);
+ result = -1;
+ goto done;
+ }
+
+ fd.ffd.reset(open("/dev/fuse", O_RDWR));
+ if (!fd.ffd) {
+ perror("open /dev/fuse");
+ result = -1;
+ goto done;
+ }
+
+ {
+ std::string opts = android::base::StringPrintf(
+ "fd=%d,user_id=%d,group_id=%d,max_read=%u,allow_other,rootmode=040000", fd.ffd.get(),
+ fd.uid, fd.gid, block_size);
+
+ result = mount("/dev/fuse", mount_point, "fuse", MS_NOSUID | MS_NODEV | MS_RDONLY | MS_NOEXEC,
+ opts.c_str());
+ if (result == -1) {
+ perror("mount");
+ goto done;
+ }
+ }
+
+ uint8_t request_buffer[sizeof(fuse_in_header) + PATH_MAX * 8];
+ for (;;) {
+ ssize_t len = TEMP_FAILURE_RETRY(read(fd.ffd, request_buffer, sizeof(request_buffer)));
+ if (len == -1) {
+ perror("read request");
+ if (errno == ENODEV) {
+ result = -1;
+ break;
+ }
+ continue;
+ }
+
+ if (static_cast<size_t>(len) < sizeof(fuse_in_header)) {
+ fprintf(stderr, "request too short: len=%zd\n", len);
+ continue;
+ }
+
+ fuse_in_header* hdr = reinterpret_cast<fuse_in_header*>(request_buffer);
+ void* data = request_buffer + sizeof(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) {
+ fuse_out_header outhdr;
+ outhdr.len = sizeof(outhdr);
+ outhdr.error = result;
+ outhdr.unique = hdr->unique;
+ TEMP_FAILURE_RETRY(write(fd.ffd, &outhdr, sizeof(outhdr)));
+ }
+ }
+
+done:
+ fd.vtab.close();
+
+ if (umount2(mount_point, MNT_DETACH) == -1) {
+ fprintf(stderr, "fuse_sideload umount failed: %s\n", strerror(errno));
+ }
+
+ free(fd.block_data);
+ free(fd.extra_block);
+
+ return result;
+}
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