[PATCH 2/3] affs: fix remount failure when there are no options changed

[Mikulas Patocka]

The patch c8f33d0bec99 ("affs: kstrdup() memory handling") checks
if the kstrdup function returns NULL due to out-of-memory condition.
However, if we are remounting a filesystem with no change to
filesystem-specific options, the parameter data is NULL. In this case,
kstrdup returns NULL (because it was passed NULL parameter), although no
out of memory condition exists. The mount syscall then fails with ENOMEM.

This patch fixes the bug. We fail with ENOMEM only if data is non-NULL.

The patch also changes the call to replace_mount_options - if we didn't
pass any filesystem-specific options, we don't call replace_mount_options
(thus we don't erase existing reported options).

Fixes: c8f33d0bec99 ("affs: kstrdup() memory handling")
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx	# v4.1+

---
 fs/affs/super.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Index: linux-4.6/fs/affs/super.c
===================================================================
--- linux-4.6.orig/fs/affs/super.c	2016-05-19 20:49:25.000000000 +0200
+++ linux-4.6/fs/affs/super.c	2016-05-19 20:56:21.000000000 +0200
@@ -528,7 +528,7 @@ affs_remount(struct super_block *sb, int
 	char			*prefix = NULL;
 
 	new_opts = kstrdup(data, GFP_KERNEL);
-	if (!new_opts)
+	if (data && !new_opts)
 		return -ENOMEM;
 
 	pr_debug("%s(flags=0x%x,opts=\"%s\")\n", __func__, *flags, data);
@@ -546,7 +546,8 @@ affs_remount(struct super_block *sb, int
 	}
 
 	flush_delayed_work(&sbi->sb_work);
-	replace_mount_options(sb, new_opts);
+	if (new_opts)
+		replace_mount_options(sb, new_opts);
 
 	sbi->s_flags = mount_flags;
 	sbi->s_mode  = mode;