ext4: sysfs: print ext4_super_block fields as little-endian

commit a4d2aadca184ece182418950d45ba4ffc7b652d2 upstream.

While working on extended rand for last_error/first_error timestamps,
I noticed that the endianess is wrong; we access the little-endian
fields in struct ext4_super_block as native-endian when we print them.

This adds a special case in ext4_attr_show() and ext4_attr_store()
to byteswap the superblock fields if needed.

In older kernels, this code was part of super.c, it got moved to
sysfs.c in linux-4.4.

Cc: stable@vger.kernel.org
Fixes: 52c198c6820f ("ext4: add sysfs entry showing whether the fs contains errors")
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index e21afd5..bdfc2a2 100644 (file)
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -278,8 +278,12 @@ static ssize_t ext4_attr_show(struct kobject *kobj,
        case attr_pointer_ui:
                if (!ptr)
                        return 0;
-               return snprintf(buf, PAGE_SIZE, "%u\n",
-                               *((unsigned int *) ptr));
+               if (a->attr_ptr == ptr_ext4_super_block_offset)
+                       return snprintf(buf, PAGE_SIZE, "%u\n",
+                                       le32_to_cpup(ptr));
+               else
+                       return snprintf(buf, PAGE_SIZE, "%u\n",
+                                       *((unsigned int *) ptr));
        case attr_pointer_atomic:
                if (!ptr)
                        return 0;
@@ -312,7 +316,10 @@ static ssize_t ext4_attr_store(struct kobject *kobj,
                ret = kstrtoul(skip_spaces(buf), 0, &t);
                if (ret)
                        return ret;
-               *((unsigned int *) ptr) = t;
+               if (a->attr_ptr == ptr_ext4_super_block_offset)
+                       *((__le32 *) ptr) = cpu_to_le32(t);
+               else
+                       *((unsigned int *) ptr) = t;
                return len;
        case attr_inode_readahead:
                return inode_readahead_blks_store(a, sbi, buf, len);