[PATCH AUTOSEL 3.18 17/18] autofs: drop dentry reference only when it is never used

From: Sasha Levin
Date: Sat Feb 23 2019 - 16:12:10 EST


From: Pan Bian <bianpan2016@xxxxxxx>

[ Upstream commit 63ce5f552beb9bdb41546b3a26c4374758b21815 ]

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.

Link: http://lkml.kernel.org/r/154725122396.11260.16053424107144453867.stgit@pluto-themaw-net
Signed-off-by: Pan Bian <bianpan2016@xxxxxxx>
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/autofs4/expire.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index 513b8e5d151cb..4cd4b20c69dbf 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -570,7 +570,6 @@ int autofs4_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;
@@ -583,6 +582,8 @@ int autofs4_expire_run(struct super_block *sb,
complete_all(&ino->expire_complete);
spin_unlock(&sbi->fs_lock);

+ dput(dentry);
+
return ret;
}

--
2.19.1