[PATCH -next 3/5] ceph: fix possible null-ptr-deref when parsing param

[Hawkins Jiawei]

According to commit "vfs: parse: deal with zero length string value",
kernel will set the param->string to null pointer in vfs_parse_fs_string()
if fs string has zero length.

Yet the problem is that, ceph_parse_mount_param() will dereferences the
param->string, without checking whether it is a null pointer, which may
trigger a null-ptr-deref bug.

This patch solves it by adding sanity check on param->string
in ceph_parse_mount_param().

Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>
---
 fs/ceph/super.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 3fc48b43cab0..341e23fe29eb 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -417,6 +417,9 @@ static int ceph_parse_mount_param(struct fs_context *fc,
 		param->string = NULL;
 		break;
 	case Opt_mds_namespace:
+		if (!param->string)
+			return invalfc(fc, "Bad value '%s' for mount option '%s'\n",
+				       param->string, param->key);
 		if (!namespace_equals(fsopt, param->string, strlen(param->string)))
 			return invalfc(fc, "Mismatching mds_namespace");
 		kfree(fsopt->mds_namespace);
-- 
2.25.1