[Cluster-devel] [PATCH -next 4/5] gfs2: 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, gfs2_parse_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 gfs2_parse_param().

Reported-by: syzbot+da97a57c5b742d05d...@syzkaller.appspotmail.com
Tested-by: syzbot+da97a57c5b742d05d...@syzkaller.appspotmail.com
Cc: agrue...@redhat.com
Cc: cluster-devel@redhat.com
Cc: linux-ker...@vger.kernel.org
Cc: rpete...@redhat.com
Cc: syzkaller-b...@googlegroups.com
Signed-off-by: Hawkins Jiawei <yin31...@gmail.com>
---
 fs/gfs2/ops_fstype.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
index c0cf1d2d0ef5..934746f18c25 100644
--- a/fs/gfs2/ops_fstype.c
+++ b/fs/gfs2/ops_fstype.c
@@ -1446,12 +1446,18 @@ static int gfs2_parse_param(struct fs_context *fc, 
struct fs_parameter *param)
 
        switch (o) {
        case Opt_lockproto:
+               if (!param->string)
+                       goto bad_val;
                strscpy(args->ar_lockproto, param->string, GFS2_LOCKNAME_LEN);
                break;
        case Opt_locktable:
+               if (!param->string)
+                       goto bad_val;
                strscpy(args->ar_locktable, param->string, GFS2_LOCKNAME_LEN);
                break;
        case Opt_hostdata:
+               if (!param->string)
+                       goto bad_val;
                strscpy(args->ar_hostdata, param->string, GFS2_LOCKNAME_LEN);
                break;
        case Opt_spectator:
@@ -1535,6 +1541,10 @@ static int gfs2_parse_param(struct fs_context *fc, 
struct fs_parameter *param)
                return invalfc(fc, "invalid mount option: %s", param->key);
        }
        return 0;
+
+bad_val:
+       return invalfc(fc, "Bad value '%s' for mount option '%s'\n",
+                      param->string, param->key);
 }
 
 static int gfs2_reconfigure(struct fs_context *fc)
-- 
2.25.1