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From 6d8c50dcb029872b298eea68cc6209c866fd3e14 Mon Sep 17 00:00:00 2001
From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Thu, 7 Jun 2018 13:39:49 -0700
Subject: [PATCH] socket: close race condition between sock_close() and
sockfs_setattr()
fchownat() doesn't even hold refcnt of fd until it figures out
fd is really needed (otherwise is ignored) and releases it after
it resolves the path. This means sock_close() could race with
sockfs_setattr(), which leads to a NULL pointer dereference
since typically we set sock->sk to NULL in ->release().
As pointed out by Al, this is unique to sockfs. So we can fix this
in socket layer by acquiring inode_lock in sock_close() and
checking against NULL in sockfs_setattr().
sock_release() is called in many places, only the sock_close()
path matters here. And fortunately, this should not affect normal
sock_close() as it is only called when the last fd refcnt is gone.
It only affects sock_close() with a parallel sockfs_setattr() in
progress, which is not common.
Fixes: 86741ec25462 ("net: core: Add a UID field to struct sock.")
Reported-by: shankarapailoor <shankarapailoor@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Lorenzo Colitti <lorenzo@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/socket.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/net/socket.c b/net/socket.c
index af57d85bcb48..8a109012608a 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -541,7 +541,10 @@ static int sockfs_setattr(struct dentry *dentry, struct iattr *iattr)
if (!err && (iattr->ia_valid & ATTR_UID)) {
struct socket *sock = SOCKET_I(d_inode(dentry));
- sock->sk->sk_uid = iattr->ia_uid;
+ if (sock->sk)
+ sock->sk->sk_uid = iattr->ia_uid;
+ else
+ err = -ENOENT;
}
return err;
@@ -590,12 +593,16 @@ EXPORT_SYMBOL(sock_alloc);
* an inode not a file.
*/
-void sock_release(struct socket *sock)
+static void __sock_release(struct socket *sock, struct inode *inode)
{
if (sock->ops) {
struct module *owner = sock->ops->owner;
+ if (inode)
+ inode_lock(inode);
sock->ops->release(sock);
+ if (inode)
+ inode_unlock(inode);
sock->ops = NULL;
module_put(owner);
}
@@ -609,6 +616,11 @@ void sock_release(struct socket *sock)
}
sock->file = NULL;
}
+
+void sock_release(struct socket *sock)
+{
+ __sock_release(sock, NULL);
+}
EXPORT_SYMBOL(sock_release);
void __sock_tx_timestamp(__u16 tsflags, __u8 *tx_flags)
@@ -1171,7 +1183,7 @@ static int sock_mmap(struct file *file, struct vm_area_struct *vma)
static int sock_close(struct inode *inode, struct file *filp)
{
- sock_release(SOCKET_I(inode));
+ __sock_release(SOCKET_I(inode), inode);
return 0;
}
--
2.17.1
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