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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+e3f23ce40269a4c9053a@syzkaller.appspotmail.com,
        Bob Peterson <rpeterso@redhat.com>,
        Andreas Gruenbacher <agruenba@redhat.com>
Subject: [PATCH 4.19 34/39] gfs2: check for empty rgrp tree in gfs2_ri_update
Date:   Thu, 10 Dec 2020 15:27:13 +0100
Message-Id: <20201210142603.961444296@linuxfoundation.org>
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From: Bob Peterson <rpeterso@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+e3f23ce40269a4c9053a@syzkaller.appspotmail.com
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@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;