libkmod: Add support for detached module signatures
diff mbox

Message ID 20160405001611.GJ21187@decadent.org.uk
State Deferred
Headers show

Commit Message

Ben Hutchings April 5, 2016, 12:16 a.m. UTC
Debian will not sign modules during the kernel package build, as this
conflicts with the goal of reproducible builds.  Instead, we will
generate detached signatures offline and include them in a second
package.

We could attach the signatures when building this second package or at
installation time, but that leads to duplication of all modules,
either in the archive or on users' systems.

To avoid this, add support to libkmod for concatenating modules with
detached signatures (files with the '.sig' extension) at load time.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
I should note that I have *not* tested this with gzip or xz
compressed modules.

Ben.

 libkmod/libkmod-file.c | 110 +++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 103 insertions(+), 7 deletions(-)

Patch
diff mbox

diff --git a/libkmod/libkmod-file.c b/libkmod/libkmod-file.c
index 5eeba6a912a2..c30a9b92a3ac 100644
--- a/libkmod/libkmod-file.c
+++ b/libkmod/libkmod-file.c
@@ -52,6 +52,7 @@  struct kmod_file {
 	gzFile gzf;
 #endif
 	int fd;
+	int sig_fd;
 	bool direct;
 	off_t size;
 	void *memory;
@@ -60,6 +61,37 @@  struct kmod_file {
 	struct kmod_elf *elf;
 };
 
+static int append_detached_sig(struct kmod_file *file, size_t buf_size)
+{
+	struct stat st;
+	ssize_t read_size;
+
+	if (file->sig_fd < 0)
+		return 0;
+
+	if (fstat(file->sig_fd, &st) < 0)
+		return -errno;
+
+	/* Grow the buffer if necessary */
+	if ((size_t)st.st_size > buf_size - file->size) {
+		void *tmp = realloc(file->memory, file->size + st.st_size);
+		if (tmp == NULL)
+			return -errno;
+		file->memory = tmp;
+	}
+
+	read_size = read(file->sig_fd, (char *)file->memory + file->size,
+			 st.st_size);
+	if (read_size < 0)
+		return -errno;
+	if (read_size != st.st_size)
+		return -EINVAL;
+
+	file->size += read_size;
+
+	return 0;
+}
+
 #ifdef ENABLE_XZ
 static void xz_uncompress_belch(struct kmod_file *file, lzma_ret ret)
 {
@@ -144,6 +176,7 @@  static int load_xz(struct kmod_file *file)
 {
 	lzma_stream strm = LZMA_STREAM_INIT;
 	lzma_ret lzret;
+	size_t buf_size;
 	int ret;
 
 	lzret = lzma_stream_decoder(&strm, UINT64_MAX, LZMA_CONCATENATED);
@@ -155,7 +188,14 @@  static int load_xz(struct kmod_file *file)
 		return -EINVAL;
 	}
 	ret = xz_uncompress(&strm, file);
+	buf_size = file->size + strm->avail_out;
 	lzma_end(&strm);
+
+	if (!ret) {
+		ret = append_detached_sig(file, buf_size);
+		if (ret)
+			free(file->memory);
+	}
 	return ret;
 }
 
@@ -214,6 +254,11 @@  static int load_zlib(struct kmod_file *file)
 
 	file->memory = p;
 	file->size = did;
+
+	err = append_detached_sig(file, total);
+	if (err)
+		goto error;
+
 	p = NULL;
 	return 0;
 
@@ -254,18 +299,50 @@  static int load_reg(struct kmod_file *file)
 	if (fstat(file->fd, &st) < 0)
 		return -errno;
 
-	file->size = st.st_size;
-	file->memory = mmap(NULL, file->size, PROT_READ, MAP_PRIVATE,
-			    file->fd, 0);
-	if (file->memory == MAP_FAILED)
-		return -errno;
-	file->direct = true;
+	if (file->sig_fd < 0) {
+		file->size = st.st_size;
+		file->memory = mmap(NULL, file->size, PROT_READ, MAP_PRIVATE,
+				    file->fd, 0);
+		if (file->memory == MAP_FAILED)
+			return -errno;
+		file->direct = true;
+	} else {
+		size_t plain_size = st.st_size, sig_size;
+		_cleanup_free_ unsigned char *p = NULL;
+		ssize_t ret;
+
+		if (fstat(file->sig_fd, &st) < 0)
+			return -errno;
+		sig_size = st.st_size;
+
+		p = malloc(plain_size + sig_size);
+		if (!p)
+			return -errno;
+
+		ret = read(file->fd, p, plain_size);
+		if (ret < 0)
+			return -errno;
+		if ((size_t)ret != plain_size)
+			return -EINVAL;
+		file->memory = p;
+		file->size = plain_size;
+
+		ret = append_detached_sig(file, plain_size + sig_size);
+		if (ret)
+			return ret;
+
+		p = NULL;
+	}
+
 	return 0;
 }
 
 static void unload_reg(struct kmod_file *file)
 {
-	munmap(file->memory, file->size);
+	if (file->direct)
+		munmap(file->memory, file->size);
+	else
+		free(file->memory);
 }
 
 static const struct file_ops reg_ops = {
@@ -285,6 +362,7 @@  struct kmod_file *kmod_file_open(const struct kmod_ctx *ctx,
 						const char *filename)
 {
 	struct kmod_file *file = calloc(1, sizeof(struct kmod_file));
+	char *sig_filename = NULL;
 	const struct comp_type *itr;
 	size_t magic_size_max = 0;
 	int err;
@@ -292,12 +370,25 @@  struct kmod_file *kmod_file_open(const struct kmod_ctx *ctx,
 	if (file == NULL)
 		return NULL;
 
+	file->sig_fd = -1;
+
 	file->fd = open(filename, O_RDONLY|O_CLOEXEC);
 	if (file->fd < 0) {
 		err = -errno;
 		goto error;
 	}
 
+	/* Try to open a detached signature.  If it's missing, that's OK. */
+	if (asprintf(&sig_filename, "%s.sig", filename) < 0) {
+		err = -errno;
+		goto error;
+	}
+	file->sig_fd = open(sig_filename, O_RDONLY|O_CLOEXEC);
+	if (file->sig_fd < 0 && errno != ENOENT) {
+		err = -errno;
+		goto error;
+	}
+
 	for (itr = comp_types; itr->ops.load != NULL; itr++) {
 		if (magic_size_max < itr->magic_size)
 			magic_size_max = itr->magic_size;
@@ -336,7 +427,10 @@  struct kmod_file *kmod_file_open(const struct kmod_ctx *ctx,
 	err = file->ops->load(file);
 	file->ctx = ctx;
 error:
+	free(sig_filename);
 	if (err < 0) {
+		if (file->sig_fd >= 0)
+			close(file->sig_fd);
 		if (file->fd >= 0)
 			close(file->fd);
 		free(file);
@@ -373,6 +467,8 @@  void kmod_file_unref(struct kmod_file *file)
 		kmod_elf_unref(file->elf);
 
 	file->ops->unload(file);
+	if (file->sig_fd >= 0)
+		close(file->sig_fd);
 	if (file->fd >= 0)
 		close(file->fd);
 	free(file);