From 504a10d9e46bc37b23d0a1ae2f28973c8516e636 Mon Sep 17 00:00:00 2001
From: Bob Peterson <rpeterso@redhat.com>
Date: Fri, 28 Apr 2023 12:07:46 -0400
Subject: [PATCH] gfs2: Don't deref jdesc in evict
Git-commit: 504a10d9e46bc37b23d0a1ae2f28973c8516e636
Patch-mainline: v6.4-rc2
References: bsc#1212265 CVE-2023-3212

On corrupt gfs2 file systems the evict code can try to reference the
journal descriptor structure, jdesc, after it has been freed and set to
NULL. The sequence of events is:

init_journal()
...
Fail_jindex: gfs2_jindex_free(sdp); <------frees journals, sets jdesc = NULL
      if (gfs2_holder_initialized(&ji_gh))
         gfs2_glock_dq_uninit(&ji_gh);
Fail: iput(sdp->sd_jindex); <--references jdesc in evict_linked_inode
      evict()
         gfs2_evict_inode()
            evict_linked_inode()
               ret = gfs2_trans_begin(sdp, 0, sdp->sd_jdesc->jd_blocks);
<------references the now freed/zeroed sd_jdesc pointer.

The call to gfs2_trans_begin is done because the truncate_inode_pages
call can cause gfs2 events that require a transaction, such as removing
journaled data (jdata) blocks from the journal.

This patch fixes the problem by adding a check for sdp->sd_jdesc to
function gfs2_evict_inode. In theory, this should only happen to corrupt
gfs2 file systems, when gfs2 detects the problem, reports it, then tries
to evict all the system inodes it has read in up to that point.

Reported-by: Yang Lan <lanyang0908@gmail.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Acked-by: Anthony Iliopoulos <ailiop@suse.com>

---
 fs/gfs2/super.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1401,6 +1401,14 @@ static void gfs2_evict_inode(struct inod
 	if (inode->i_nlink || sb_rdonly(sb))
 		goto out;
 
+	/*
+	 * In case of an incomplete mount, gfs2_evict_inode() may be called for
+	 * system files without having an active journal to write to.  In that
+	 * case, skip the filesystem evict.
+	 */
+	if (!sdp->sd_jdesc)
+		goto out;
+
 	gfs2_holder_mark_uninitialized(&gh);
 	ret = evict_should_delete(inode, &gh);
 	if (ret == SHOULD_DEFER_EVICTION)