[PATCH 4.19 34/39] gfs2: check for empty rgrp tree in gfs2_ri_update

[Greg Kroah-Hartman]

From: Bob Peterson <rpete...@redhat.com>

commit 778721510e84209f78e31e2ccb296ae36d623f5e upstream.

If gfs2 tries to mount a (corrupt) file system that has no resource
groups it still tries to set preferences on the first one, which causes
a kernel null pointer dereference. This patch adds a check to function
gfs2_ri_update so this condition is detected and reported back as an
error.

Reported-by: syzbot+e3f23ce40269a4c90...@syzkaller.appspotmail.com
Signed-off-by: Bob Peterson <rpete...@redhat.com>
Signed-off-by: Andreas Gruenbacher <agrue...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 fs/gfs2/rgrp.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -1009,6 +1009,10 @@ static int gfs2_ri_update(struct gfs2_in
        if (error < 0)
                return error;
 
+       if (RB_EMPTY_ROOT(&sdp->sd_rindex_tree)) {
+               fs_err(sdp, "no resource groups found in the file system.\n");
+               return -ENOENT;
+       }
        set_rgrp_preferences(sdp);
 
        sdp->sd_rindex_uptodate = 1;