4 files changed, 23 insertions, 3 deletions

diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index d8d8e7ba6a1e..eb1cc92cd67d 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -110,6 +110,7 @@ struct autofs_sb_info {
         int sub_version;
         int min_proto;
         int max_proto;
+        int compat_daemon;
         unsigned long exp_timeout;
         unsigned int type;
         int reghost_enabled;
diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
index 76741d8d7786..85f1fcdb30e7 100644
--- a/fs/autofs4/dev-ioctl.c
+++ b/fs/autofs4/dev-ioctl.c
@@ -385,6 +385,7 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
                 sbi->pipefd = pipefd;
                 sbi->pipe = pipe;
                 sbi->catatonic = 0;
+                sbi->compat_daemon = is_compat_task();
         }
 out:
         mutex_unlock(&sbi->wq_mutex);
diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
index e16980b00b8d..06858d955120 100644
--- a/fs/autofs4/inode.c
+++ b/fs/autofs4/inode.c
@@ -19,6 +19,7 @@
 #include <linux/parser.h>
 #include <linux/bitops.h>
 #include <linux/magic.h>
+#include <linux/compat.h>
 #include "autofs_i.h"
 #include <linux/module.h>
 
@@ -224,6 +225,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
         set_autofs_type_indirect(&sbi->type);
         sbi->min_proto = 0;
         sbi->max_proto = 0;
+        sbi->compat_daemon = is_compat_task();
         mutex_init(&sbi->wq_mutex);
         mutex_init(&sbi->pipe_mutex);
         spin_lock_init(&sbi->fs_lock);
diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index da8876d38a7b..9c098db43344 100644
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -91,7 +91,24 @@ static int autofs4_write(struct autofs_sb_info *sbi,
 
         return (bytes > 0);
 }
-        
+
+/*
+ * The autofs_v5 packet was misdesigned.
+ *
+ * The packets are identical on x86-32 and x86-64, but have different
+ * alignment. Which means that 'sizeof()' will give different results.
+ * Fix it up for the case of running 32-bit user mode on a 64-bit kernel.
+ */
+static noinline size_t autofs_v5_packet_size(struct autofs_sb_info *sbi)
+{
+        size_t pktsz = sizeof(struct autofs_v5_packet);
+#if defined(CONFIG_X86_64) && defined(CONFIG_COMPAT)
+        if (sbi->compat_daemon > 0)
+                pktsz -= 4;
+#endif
+        return pktsz;
+}
+
 static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
                                  struct autofs_wait_queue *wq,
                                  int type)
@@ -155,8 +172,7 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
         {
                 struct autofs_v5_packet *packet = &pkt.v5_pkt.v5_packet;
 
-                pktsz = sizeof(*packet);
-
+                pktsz = autofs_v5_packet_size(sbi);
                 packet->wait_queue_token = wq->wait_queue_token;
                 packet->len = wq->name.len;
                 memcpy(packet->name, wq->name.name, wq->name.len);