Fix migration of fds to ELF files

criu/files-reg.c

@@ -1650,39 +1650,36 @@ static int get_build_id_64(Elf64_Ehdr *file_header, unsigned char **build_id, co
  */
 static int get_build_id(const int fd, const struct stat *fd_status, unsigned char **build_id)
 {
-	char buf[SELFMAG + 1];
-	void *start_addr;
+	char *start_addr;
 	size_t mapped_size;
 	int ret = -1;
 
-	if (read(fd, buf, SELFMAG + 1) != SELFMAG + 1)
-		return -1;
-
-	/*
-	 * The first 4 bytes contain a magic number identifying the file as an
-	 * ELF file. They should contain the characters ‘\x7f’, ‘E’, ‘L’, and
-	 * ‘F’, respectively. These characters are together defined as ELFMAG.
-	 */
-	if (strncmp(buf, ELFMAG, SELFMAG))
-		return -1;
-
 	/*
 	 * If the build-id exists, then it will most likely be present in the
 	 * beginning of the file. Therefore at most only the first 1 MB of the
 	 * file is mapped.
 	 */
 	mapped_size = min_t(size_t, fd_status->st_size, BUILD_ID_MAP_SIZE);
 	start_addr = mmap(0, mapped_size, PROT_READ, MAP_PRIVATE | MAP_FILE, fd, 0);
-	if (start_addr == MAP_FAILED) {
+	if ((void*)start_addr == MAP_FAILED) {
 		pr_warn("Couldn't mmap file with fd %d\n", fd);
 		return -1;
 	}
 
-	if (buf[EI_CLASS] == ELFCLASS32)
-		ret = get_build_id_32(start_addr, build_id, fd, mapped_size);
-	if (buf[EI_CLASS] == ELFCLASS64)
-		ret = get_build_id_64(start_addr, build_id, fd, mapped_size);
+	/*
+	 * The first 4 bytes contain a magic number identifying the file as an
+	 * ELF file. They should contain the characters ‘\x7f’, ‘E’, ‘L’, and
+	 * ‘F’, respectively. These characters are together defined as ELFMAG.
+	 */
+	if (memcmp(start_addr, ELFMAG, SELFMAG))
+		goto out;
 
+	if (start_addr[EI_CLASS] == ELFCLASS32)
+		ret = get_build_id_32((Elf32_Ehdr *)start_addr, build_id, fd, mapped_size);
+	if (start_addr[EI_CLASS] == ELFCLASS64)
+		ret = get_build_id_64((Elf64_Ehdr *)start_addr, build_id, fd, mapped_size);
+
+out:
 	munmap(start_addr, mapped_size);
 	return ret;
 }

test/zdtm/lib/lock.h

@@ -7,6 +7,7 @@
 #include <sys/time.h>
 #include <limits.h>
 #include <errno.h>
+#include <signal.h>
 #include "asm/atomic.h"
 
 #define BUG_ON(condition)                                                        \

test/zdtm/static/Makefile

@@ -269,6 +269,7 @@ TST_NOFILE	:=				\
 		sigtrap				\
 		sigtrap01			\
 		change_mnt_context		\
+		fd_offset			\
 #		jobctl00			\
 
 PKG_CONFIG ?= pkg-config

test/zdtm/static/fd_offset.c

@@ -0,0 +1,42 @@
+#include <fcntl.h>
+
+#include "zdtmtst.h"
+#include "lock.h"
+
+const char *test_doc = "Check that criu properly restores offsets on ELF files";
+const char *test_author = "Michal Clapinski <[email protected]>";
+
+void check_offset(int fd)
+{
+	int offset = lseek(fd, 0, SEEK_CUR);
+	if (offset < 0) {
+		fail("lseek");
+		exit(1);
+	}
+	if (offset != 0) {
+		fail("wrong offset; expected: 0, got: %d", offset);
+		exit(1);
+	}
+}
+
+int main(int argc, char **argv)
+{
+	int fd;
+
+	test_init(argc, argv);
+
+	fd = open("/proc/self/exe", O_RDONLY);
+	if (fd < 0) {
+		fail("open");
+		exit(1);
+	}
+	check_offset(fd);
+
+	test_daemon();
+	test_waitsig();
+
+	check_offset(fd);
+
+	pass();
+	return 0;
+}