linux-kernel - [PATCH 1/3] autofs: drop dentry reference only when it is never used

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Date:   Sat, 12 Jan 2019 08:00:24 +0800
From:   Ian Kent <raven@...maw.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     autofs mailing list <autofs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pan Bian <bianpan2016@....com>
Subject: [PATCH 1/3] autofs: drop dentry reference only when it is never used

From: Pan Bian <bianpan2016@....com>

The function autofs_expire_run calls dput(dentry) to drop the reference
count of dentry. However, dentry is read via autofs_dentry_ino(dentry)
after that. This may result in a use-free-bug. The patch drops the
reference count of dentry only when it is never used.

Signed-off-by: Pan Bian <bianpan2016@....com>
Acked-by: Ian Kent <raven@...maw.net>
---
 fs/autofs/expire.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/autofs/expire.c b/fs/autofs/expire.c
index d441244b79df..28d9c2b1b3bb 100644
--- a/fs/autofs/expire.c
+++ b/fs/autofs/expire.c
@@ -596,7 +596,6 @@ int autofs_expire_run(struct super_block *sb,
 	pkt.len = dentry->d_name.len;
 	memcpy(pkt.name, dentry->d_name.name, pkt.len);
 	pkt.name[pkt.len] = '\0';
-	dput(dentry);
 
 	if (copy_to_user(pkt_p, &pkt, sizeof(struct autofs_packet_expire)))
 		ret = -EFAULT;
@@ -609,6 +608,8 @@ int autofs_expire_run(struct super_block *sb,
 	complete_all(&ino->expire_complete);
 	spin_unlock(&sbi->fs_lock);
 
+	dput(dentry);
+
 	return ret;
 }