cramfs: error message about endianess

The README file in the cramfs subdirectory says: "All data is currently in
host-endian format; neither mkcramfs nor the kernel ever do swabbing."

If somebody tries to mount a cramfs with the wrong endianess, cramfs only
complains about a wrong magic but doesn't inform the user that only the
endianess isn't right.

The following patch adds an error message to the cramfs sources.  If a user
tries to mount a cramfs with the wrong endianess using the patched sources,
cramfs will display the message "cramfs: wrong endianess".

Signed-off-by: Andi Drebes <lists-receive@programmierforen.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 11 insertions, 1 deletions

diff --git a/fs/cramfs/inode.c b/fs/cramfs/inode.c
index 3d194a2be3f5..5c817bd08389 100644
--- a/fs/cramfs/inode.c
+++ b/fs/cramfs/inode.c
@@ -258,12 +258,21 @@ static int cramfs_fill_super(struct super_block *sb, void *data, int silent)
 
         /* Do sanity checks on the superblock */
         if (super.magic != CRAMFS_MAGIC) {
+                /* check for wrong endianess */
+                if (super.magic == CRAMFS_MAGIC_WEND) {
+                        if (!silent)
+                                printk(KERN_ERR "cramfs: wrong endianess\n");
+                        goto out;
+                }
+
                 /* check at 512 byte offset */
                 mutex_lock(&read_mutex);
                 memcpy(&super, cramfs_read(sb, 512, sizeof(super)), sizeof(super));
                 mutex_unlock(&read_mutex);
                 if (super.magic != CRAMFS_MAGIC) {
-                        if (!silent)
+                        if (super.magic == CRAMFS_MAGIC_WEND && !silent)
+                                printk(KERN_ERR "cramfs: wrong endianess\n");
+                        else if (!silent)
                                 printk(KERN_ERR "cramfs: wrong magic\n");
                         goto out;
                 }
diff --git a/include/linux/cramfs_fs.h b/include/linux/cramfs_fs.h
index 1dba681e428d..3be4e5a27d82 100644
--- a/include/linux/cramfs_fs.h
+++ b/include/linux/cramfs_fs.h
@@ -4,6 +4,7 @@
 #include <linux/types.h>
 
 #define CRAMFS_MAGIC            0x28cd3d45      /* some random number */
+#define CRAMFS_MAGIC_WEND       0x453dcd28      /* magic number with the wrong endianess */
 #define CRAMFS_SIGNATURE        "Compressed ROMFS"
 
 /*