linux-kernel - [PATCH AUTOSEL 4.14 16/35] jffs2: fix use-after-free on symlink traversal

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Date:   Wed, 24 Apr 2019 10:46:50 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Al Viro <viro@...iv.linux.org.uk>, Sasha Levin <sashal@...nel.org>,
        linux-mtd@...ts.infradead.org
Subject: [PATCH AUTOSEL 4.14 16/35] jffs2: fix use-after-free on symlink traversal

From: Al Viro <viro@...iv.linux.org.uk>

[ Upstream commit 4fdcfab5b5537c21891e22e65996d4d0dd8ab4ca ]

free the symlink body after the same RCU delay we have for freeing the
struct inode itself, so that traversal during RCU pathwalk wouldn't step
into freed memory.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/jffs2/readinode.c | 5 -----
 fs/jffs2/super.c     | 5 ++++-
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/fs/jffs2/readinode.c b/fs/jffs2/readinode.c
index 389ea53ea487..bccfc40b3a74 100644
--- a/fs/jffs2/readinode.c
+++ b/fs/jffs2/readinode.c
@@ -1414,11 +1414,6 @@ void jffs2_do_clear_inode(struct jffs2_sb_info *c, struct jffs2_inode_info *f)
 
 	jffs2_kill_fragtree(&f->fragtree, deleted?c:NULL);
 
-	if (f->target) {
-		kfree(f->target);
-		f->target = NULL;
-	}
-
 	fds = f->dents;
 	while(fds) {
 		fd = fds;
diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
index 83340496645b..9a9f30eddbbb 100644
--- a/fs/jffs2/super.c
+++ b/fs/jffs2/super.c
@@ -47,7 +47,10 @@ static struct inode *jffs2_alloc_inode(struct super_block *sb)
 static void jffs2_i_callback(struct rcu_head *head)
 {
 	struct inode *inode = container_of(head, struct inode, i_rcu);
-	kmem_cache_free(jffs2_inode_cachep, JFFS2_INODE_INFO(inode));
+	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
+
+	kfree(f->target);
+	kmem_cache_free(jffs2_inode_cachep, f);
 }
 
 static void jffs2_destroy_inode(struct inode *inode)
-- 
2.19.1