[PATCH v4 4/6] initramfs: Refactor to use hex2bin() instead of custom approach

David Disseldorp
2026-03-29T10:53:46Z

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

There is a simple_strntoul() function used solely as a shortcut
for hex2bin() with proper endianess conversions. Replace that
and drop the unneeded function in the next changes.

This implementation will abort if we fail to parse the cpio header,
instead of using potentially bogus header values.

Co-developed-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
init/initramfs.c | 44 +++++++++++++++++++++++++------------------
init/initramfs_test.c | 23 ++++------------------
2 files changed, 30 insertions(+), 37 deletions(-)

diff --git a/init/initramfs.c b/init/initramfs.c
index 4ed796566cf35..0d38ea8e63a29 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -6,6 +6,7 @@
#include <linux/fcntl.h>
#include <linux/file.h>
#include <linux/fs.h>
+#include <linux/hex.h>
#include <linux/init.h>
#include <linux/init_syscalls.h>
#include <linux/kstrtox.h>
@@ -21,6 +22,8 @@
#include <linux/umh.h>
#include <linux/utime.h>

+#include <asm/byteorder.h>
+
#include "do_mounts.h"
#include "initramfs_internal.h"

@@ -190,26 +193,30 @@ static __initdata gid_t gid;
static __initdata unsigned rdev;
static __initdata u32 hdr_csum;

-static void __init parse_header(char *s)
+static int __init parse_header(char *s)
{
- unsigned long parsed[13];
- int i;
+ __be32 header[13];
+ int ret;

- for (i = 0, s += 6; i < 13; i++, s += 8)
- parsed[i] = simple_strntoul(s, NULL, 16, 8);
+ ret = hex2bin((u8 *)header, s + 6, sizeof(header));
+ if (ret) {
+ error("damaged header");
+ return ret;
+ }

- ino = parsed[0];
- mode = parsed[1];
- uid = parsed[2];
- gid = parsed[3];
- nlink = parsed[4];
- mtime = parsed[5]; /* breaks in y2106 */
- body_len = parsed[6];
- major = parsed[7];
- minor = parsed[8];
- rdev = new_encode_dev(MKDEV(parsed[9], parsed[10]));
- name_len = parsed[11];
- hdr_csum = parsed[12];
+ ino = be32_to_cpu(header[0]);
+ mode = be32_to_cpu(header[1]);
+ uid = be32_to_cpu(header[2]);
+ gid = be32_to_cpu(header[3]);
+ nlink = be32_to_cpu(header[4]);
+ mtime = be32_to_cpu(header[5]); /* breaks in y2106 */
+ body_len = be32_to_cpu(header[6]);
+ major = be32_to_cpu(header[7]);
+ minor = be32_to_cpu(header[8]);
+ rdev = new_encode_dev(MKDEV(be32_to_cpu(header[9]), be32_to_cpu(header[10])));
+ name_len = be32_to_cpu(header[11]);
+ hdr_csum = be32_to_cpu(header[12]);
+ return 0;
}

/* FSM */
@@ -289,7 +296,8 @@ static int __init do_header(void)
error("no cpio magic");
return 1;
}
- parse_header(collected);
+ if (parse_header(collected))
+ return 1;
next_header = this_header + N_ALIGN(name_len) + body_len;
next_header = (next_header + 3) & ~3;
state = SkipIt;
diff --git a/init/initramfs_test.c b/init/initramfs_test.c
index 4a7a85560ee50..4785423f601c2 100644
--- a/init/initramfs_test.c
+++ b/init/initramfs_test.c
@@ -31,7 +31,8 @@ struct initramfs_test_cpio {
#define CPIO_HDR_FMT "%s%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%s"
/*
* bogus newc header with "0x" prefixes on the uid, gid and namesize values.
- * parse_header()/simple_str[n]toul() accept this.
+ * parse_header()/simple_str[n]toul() accepted this, contrary to the initramfs
+ * specification. hex2bin() now fails.
*/
#define CPIO_HDR_OX_INJECT \
"%s%08x%08x0x%06x0X%06x%08x%08x%08x%08x%08x%08x%08x0x%06x%08x%s"
@@ -507,8 +508,7 @@ static void __init initramfs_test_hdr_hex(struct kunit *test)
{
char *err;
size_t len;
- struct kstat st0, st1;
- char fdata[] = "this file data will be unpacked";
+ char fdata[] = "this file data will not be unpacked";
struct initramfs_test_bufs {
char cpio_src[(CPIO_HDRLEN + PATH_MAX + 3 + sizeof(fdata)) * 2];
} *tbufs = kzalloc(sizeof(struct initramfs_test_bufs), GFP_KERNEL);
@@ -538,22 +538,7 @@ static void __init initramfs_test_hdr_hex(struct kunit *test)
len = fill_cpio(c, ARRAY_SIZE(c), true, tbufs->cpio_src);

err = unpack_to_rootfs(tbufs->cpio_src, len);
- KUNIT_EXPECT_NULL(test, err);
-
- KUNIT_EXPECT_EQ(test, init_stat(c[0].fname, &st0, 0), 0);
- KUNIT_EXPECT_EQ(test, init_stat(c[1].fname, &st1, 0), 0);
-
- KUNIT_EXPECT_TRUE(test,
- uid_eq(st0.uid, make_kuid(current_user_ns(), (uid_t)0x123456)));
- KUNIT_EXPECT_TRUE(test,
- gid_eq(st0.gid, make_kgid(current_user_ns(), (gid_t)0x123457)));
- KUNIT_EXPECT_TRUE(test,
- uid_eq(st1.uid, make_kuid(current_user_ns(), (uid_t)0x56)));
- KUNIT_EXPECT_TRUE(test,
- gid_eq(st1.gid, make_kgid(current_user_ns(), (gid_t)0x57)));
-
- KUNIT_EXPECT_EQ(test, init_unlink(c[0].fname), 0);
- KUNIT_EXPECT_EQ(test, init_rmdir(c[1].fname), 0);
+ KUNIT_EXPECT_NOT_NULL(test, err);

kfree(tbufs);
}
--
2.51.0