[PATCH v3 2/2] initramfs: introduce do_readxattrs()

[Roberto Sassu <roberto.sassu@huawei.com>]

This patch adds support for an alternative method to add xattrs to files in
the rootfs filesystem. Instead of extracting them directly from the ram
disk image, they are extracted from a regular file called .xattr-list, that
can be added by any ram disk generator available today. The file format is:

<file #N data len (ASCII, 10 chars)><file #N path>\0
<xattr #N data len (ASCII, 8 chars)><xattr #N name>\0<xattr #N value>

.xattr-list can be generated by executing:

$ getfattr --absolute-names -d -h -R -e hex -m - \
      <file list> | xattr.awk -b > ${initdir}/.xattr-list

where the content of the xattr.awk script is:

#! /usr/bin/awk -f
{
  if (!length($0)) {
    printf("%.10x%s\0", len, file);
    for (x in xattr) {
      printf("%.8x%s\0", xattr_len[x], x);
      for (i = 0; i < length(xattr[x]) / 2; i++) {
        printf("%c", strtonum("0x"substr(xattr[x], i * 2 + 1, 2)));
      }
    }
    i = 0;
    delete xattr;
    delete xattr_len;
    next;
  };
  if (i == 0) {
    file=$3;
    len=length(file) + 8 + 1;
  }
  if (i > 0) {
    split($0, a, "=");
    xattr[a[1]]=substr(a[2], 3);
    xattr_len[a[1]]=length(a[1]) + 1 + 8 + length(xattr[a[1]]) / 2;
    len+=xattr_len[a[1]];
  };
  i++;
}

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 init/initramfs.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)

diff --git a/init/initramfs.c b/init/initramfs.c
index 0c6dd1d5d3f6..6ec018c6279a 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -13,6 +13,8 @@
 #include <linux/namei.h>
 #include <linux/xattr.h>
 
+#define XATTR_LIST_FILENAME ".xattr-list"
+
 static ssize_t __init xwrite(int fd, const char *p, size_t count)
 {
 	ssize_t out = 0;
@@ -382,6 +384,97 @@ static int __init __maybe_unused do_setxattrs(char *pathname)
 	return 0;
 }
 
+struct path_hdr {
+	char p_size[10]; /* total size including p_size field */
+	char p_data[];   /* <path>\0<xattrs> */
+};
+
+static int __init do_readxattrs(void)
+{
+	struct path_hdr hdr;
+	char *path = NULL;
+	char str[sizeof(hdr.p_size) + 1];
+	unsigned long file_entry_size;
+	size_t size, path_size, total_size;
+	struct kstat st;
+	struct file *file;
+	loff_t pos;
+	int ret;
+
+	ret = vfs_lstat(XATTR_LIST_FILENAME, &st);
+	if (ret < 0)
+		return ret;
+
+	total_size = st.size;
+
+	file = filp_open(XATTR_LIST_FILENAME, O_RDONLY, 0);
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+
+	pos = file->f_pos;
+
+	while (total_size) {
+		size = kernel_read(file, (char *)&hdr, sizeof(hdr), &pos);
+		if (size != sizeof(hdr)) {
+			ret = -EIO;
+			goto out;
+		}
+
+		total_size -= size;
+
+		str[sizeof(hdr.p_size)] = 0;
+		memcpy(str, hdr.p_size, sizeof(hdr.p_size));
+		ret = kstrtoul(str, 16, &file_entry_size);
+		if (ret < 0)
+			goto out;
+
+		file_entry_size -= sizeof(sizeof(hdr.p_size));
+		if (file_entry_size > total_size) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		path = vmalloc(file_entry_size);
+		if (!path) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		size = kernel_read(file, path, file_entry_size, &pos);
+		if (size != file_entry_size) {
+			ret = -EIO;
+			goto out_free;
+		}
+
+		total_size -= size;
+
+		path_size = strnlen(path, file_entry_size);
+		if (path_size == file_entry_size) {
+			ret = -EINVAL;
+			goto out_free;
+		}
+
+		xattr_buf = path + path_size + 1;
+		xattr_len = file_entry_size - path_size - 1;
+
+		ret = do_setxattrs(path);
+		vfree(path);
+		path = NULL;
+
+		if (ret < 0)
+			break;
+	}
+out_free:
+	vfree(path);
+out:
+	fput(file);
+
+	if (ret < 0)
+		error("Unable to parse xattrs");
+
+	return ret;
+}
+
 static __initdata int wfd;
 
 static int __init do_name(void)
@@ -391,6 +484,11 @@ static int __init do_name(void)
 	if (strcmp(collected, "TRAILER!!!") == 0) {
 		free_hash();
 		return 0;
+	} else if (strcmp(collected, XATTR_LIST_FILENAME) == 0) {
+		struct kstat st;
+
+		if (!vfs_lstat(collected, &st))
+			do_readxattrs();
 	}
 	clean_path(collected, mode);
 	if (S_ISREG(mode)) {
@@ -562,6 +660,7 @@ static char * __init unpack_to_rootfs(char *buf, unsigned long len)
 		buf += my_inptr;
 		len -= my_inptr;
 	}
+	do_readxattrs();
 	dir_utime();
 	kfree(name_buf);
 	kfree(symlink_buf);
-- 
2.17.1