[PATCH] fs/jffs2: Fix NULL deref in jffs2_scan_dirty_space

[Artem Chernyshev]

As was mentioned in 2ebf09c2, it is possible to get oops,
when marking space dirty in scan, but no previous node exists

It still can be in jffs2_link_node_ref() via deref jeb->last_node.
Since all jffs2_scan_dirty_space() callers check value of a
function, we can return error code safely.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Artem Chernyshev <artem.chernyshev@xxxxxxxxxxx>
---
 fs/jffs2/nodelist.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/jffs2/nodelist.c b/fs/jffs2/nodelist.c
index b86c78d178c6..6bebf1d64000 100644
--- a/fs/jffs2/nodelist.c
+++ b/fs/jffs2/nodelist.c
@@ -669,8 +669,11 @@ int jffs2_scan_dirty_space(struct jffs2_sb_info *c, struct jffs2_eraseblock *jeb
 			size, jeb->free_size, jeb->wasted_size);
 		BUG();
 	}
+	if (!jeb->last_node) {
+		return -EINVAL;
+	}
 	/* REF_EMPTY_NODE is !obsolete, so that works OK */
-	if (jeb->last_node && ref_obsolete(jeb->last_node)) {
+	if (ref_obsolete(jeb->last_node) {
 #ifdef TEST_TOTLEN
 		jeb->last_node->__totlen += size;
 #endif
-- 
2.37.3