Merge pull request #2698 from brauner/2018-10-17/config_parsing

parse: protect against config updates during parse

src/lxc/conf.c

@@ -3344,9 +3344,8 @@ void remount_all_slave(void)
 		}
 	}
 
-#define __LXC_SENDFILE_MAX 0x7ffff000 /* maximum number of bytes sendfile can handle */
 again:
-	copied = sendfile(memfd, mntinfo_fd, NULL, __LXC_SENDFILE_MAX);
+	copied = lxc_sendfile_nointr(memfd, mntinfo_fd, NULL, LXC_SENDFILE_MAX);
 	if (copied < 0) {
 		if (errno == EINTR)
 			goto again;

src/lxc/file_utils.c

@@ -25,6 +25,7 @@
 #include <linux/magic.h>
 #include <stdlib.h>
 #include <sys/stat.h>
+#include <sys/sendfile.h>
 #include <sys/types.h>
 
 #include "config.h"
@@ -313,3 +314,19 @@ FILE *fopen_cloexec(const char *path, const char *mode)
 	errno = saved_errno;
 	return ret;
 }
+
+ssize_t lxc_sendfile_nointr(int out_fd, int in_fd, off_t *offset, size_t count)
+{
+	ssize_t ret;
+
+again:
+	ret = sendfile(out_fd, in_fd, offset, count);
+	if (ret < 0) {
+		if (errno == EINTR)
+			goto again;
+
+		return -1;
+	}
+
+	return ret;
+}

src/lxc/file_utils.h

@@ -53,5 +53,7 @@ extern bool has_fs_type(const char *path, fs_type_magic magic_val);
 extern bool fhas_fs_type(int fd, fs_type_magic magic_val);
 extern bool is_fs_type(const struct statfs *fs, fs_type_magic magic_val);
 extern FILE *fopen_cloexec(const char *path, const char *mode);
+extern ssize_t lxc_sendfile_nointr(int out_fd, int in_fd, off_t *offset,
+				   size_t count);
 
 #endif /* __LXC_FILE_UTILS_H */

src/lxc/macro.h

@@ -389,4 +389,7 @@ enum {
 #define STRLITERALLEN(x) (sizeof(""x"") - 1)
 #define STRARRAYLEN(x) (sizeof(x) - 1)
 
+/* Maximum number of bytes sendfile() is able to send in one go. */
+#define LXC_SENDFILE_MAX 0x7ffff000
+
 #endif /* __LXC_MACRO_H */

src/lxc/parse.c

@@ -30,10 +30,14 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
+#include <sys/sendfile.h>
 
 #include "config.h"
+#include "file_utils.h"
 #include "log.h"
+#include "macro.h"
 #include "parse.h"
+#include "syscall_wrappers.h"
 #include "utils.h"
 
 lxc_log_define(parse, lxc);
@@ -67,35 +71,67 @@ int lxc_strmunmap(void *addr, size_t length)
 
 int lxc_file_for_each_line_mmap(const char *file, lxc_file_cb callback, void *data)
 {
-	int fd, saved_errno;
-	char *buf, *line;
-	struct stat st;
-	int ret = 0;
+	int saved_errno;
+	ssize_t ret, bytes_sent;
+	char *line;
+	int fd = -1, memfd = -1;
+	char *buf = NULL;
+
+	memfd = memfd_create(".lxc_config_file", MFD_CLOEXEC);
+	if (memfd < 0) {
+		char template[] = P_tmpdir "/.lxc_config_file_XXXXXX";
+
+		if (errno != ENOSYS) {
+			SYSERROR("Failed to create memory file");
+			goto on_error;
+		}
+
+		TRACE("Failed to create in-memory file. Falling back to "
+		      "temporary file");
+		memfd = lxc_make_tmpfile(template, true);
+		if (memfd < 0) {
+			SYSERROR("Failed to create temporary file \"%s\"", template);
+			goto on_error;
+		}
+	}
 
 	fd = open(file, O_RDONLY | O_CLOEXEC);
 	if (fd < 0) {
-		SYSERROR("Failed to open config file \"%s\"", file);
+		SYSERROR("Failed to open file \"%s\"", file);
 		return -1;
 	}
 
-	ret = fstat(fd, &st);
-	if (ret < 0) {
-		SYSERROR("Failed to stat config file \"%s\"", file);
-		goto on_error_fstat;
-	}
 
-	ret = 0;
-	if (st.st_size == 0)
-		goto on_error_fstat;
-
-	ret = -1;
-	buf = lxc_strmmap(NULL, st.st_size, PROT_READ | PROT_WRITE,
-			  MAP_PRIVATE | MAP_POPULATE, fd, 0);
-	if (buf == MAP_FAILED) {
-		SYSERROR("Failed to map config file \"%s\"", file);
+	/* sendfile() handles up to 2GB. No config file should be that big. */
+	bytes_sent = lxc_sendfile_nointr(memfd, fd, NULL, LXC_SENDFILE_MAX);
+	if (bytes_sent < 0) {
+		SYSERROR("Failed to sendfile \"%s\"", file);
 		goto on_error;
 	}
 
+	ret = lxc_write_nointr(memfd, "\0", 1);
+	if (ret < 0) {
+		SYSERROR("Failed to append zero byte");
+		goto on_error;
+	}
+	bytes_sent++;
+
+	ret = lseek(memfd, 0, SEEK_SET);
+	if (ret < 0) {
+		SYSERROR("Failed to lseek");
+		goto on_error;
+	}
+
+	ret = -1;
+	buf = mmap(NULL, bytes_sent, PROT_READ | PROT_WRITE,
+		   MAP_SHARED | MAP_POPULATE, memfd, 0);
+	if (buf == MAP_FAILED) {
+		buf = NULL;
+		SYSERROR("Failed to mmap");
+		goto on_error;
+	}
+
+	ret = 0;
 	lxc_iterate_parts(line, buf, "\n\0") {
 		ret = callback(line, data);
 		if (ret) {
@@ -104,22 +140,22 @@ int lxc_file_for_each_line_mmap(const char *file, lxc_file_cb callback, void *da
 			 */
 			if (ret < 0)
 				ERROR("Failed to parse config file \"%s\" at "
-				      "line \"%s\"",
-				      file, line);
+				      "line \"%s\"", file, line);
 			break;
 		}
 	}
 
 on_error:
-	if (lxc_strmunmap(buf, st.st_size) < 0) {
-		SYSERROR("Failed to unmap config file \"%s\"", file);
+	saved_errno = errno;
+	if (fd >= 0)
+		close(fd);
+	if (memfd >= 0)
+		close(memfd);
+	if (buf && munmap(buf, bytes_sent)) {
+		SYSERROR("Failed to unmap");
 		if (ret == 0)
 			ret = -1;
 	}
-
-on_error_fstat:
-	saved_errno = errno;
-	close(fd);
 	errno = saved_errno;
 
 	return ret;