Subject: CVE-2021-47068: net/nfc: fix use-after-free llcp_sock_bind/connect

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

net/nfc: fix use-after-free llcp_sock_bind/connect

Commits 8a4cd82d ("nfc: fix refcount leak in llcp_sock_connect()")
and c33b1cc62 ("nfc: fix refcount leak in llcp_sock_bind()")
fixed a refcount leak bug in bind/connect but introduced a
use-after-free if the same local is assigned to 2 different sockets.

This can be triggered by the following simple program:
    int sock1 = socket( AF_NFC, SOCK_STREAM, NFC_SOCKPROTO_LLCP );
    int sock2 = socket( AF_NFC, SOCK_STREAM, NFC_SOCKPROTO_LLCP );
    memset( &addr, 0, sizeof(struct sockaddr_nfc_llcp) );
    addr.sa_family = AF_NFC;
    addr.nfc_protocol = NFC_PROTO_NFC_DEP;
    bind( sock1, (struct sockaddr*) &addr, sizeof(struct sockaddr_nfc_llcp) )
    bind( sock2, (struct sockaddr*) &addr, sizeof(struct sockaddr_nfc_llcp) )
    close(sock1);
    close(sock2);

Fix this by assigning NULL to llcp_sock->local after calling
nfc_llcp_local_put.

This addresses CVE-2021-23134.

The Linux kernel CVE team has assigned CVE-2021-47068 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 4.4.267 with commit a1cdd18c49d2 and fixed in 4.4.269 with commit 26157c82ba75
	Issue introduced in 4.9.267 with commit 18013007b596 and fixed in 4.9.269 with commit ccddad6dd285
	Issue introduced in 4.14.231 with commit 538a6ff11516 and fixed in 4.14.233 with commit 18ae4a192a44
	Issue introduced in 4.19.187 with commit adbb1d218c5f and fixed in 4.19.191 with commit 48fba458fe54
	Issue introduced in 5.4.112 with commit c89903c9eff2 and fixed in 5.4.119 with commit e32352070bca
	Issue introduced in 5.10.30 with commit 6fb003e5ae18 and fixed in 5.10.37 with commit 6b7021ed36da
	Issue introduced in 5.11.14 with commit 8c9e4971e142 and fixed in 5.11.21 with commit 374cdde4dcc9
	Issue introduced in 5.12 with commit c33b1cc62ac0 and fixed in 5.12.4 with commit 18175fe17ae0
	Issue introduced in 5.12 with commit c33b1cc62ac0 and fixed in 5.13 with commit c61760e6940d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47068
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/nfc/llcp_sock.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/26157c82ba756767b2bd66d28a71b1bc454447f6
	https://git.kernel.org/stable/c/ccddad6dd28530e716448e594c9ca7c76ccd0570
	https://git.kernel.org/stable/c/18ae4a192a4496e48a5490b52812645d2413307c
	https://git.kernel.org/stable/c/48fba458fe54cc2a980a05c13e6c19b8b2cfb610
	https://git.kernel.org/stable/c/e32352070bcac22be6ed8ab635debc280bb65b8c
	https://git.kernel.org/stable/c/6b7021ed36dabf29e56842e3408781cd3b82ef6e
	https://git.kernel.org/stable/c/374cdde4dcc9c909a60713abdbbf96d5e3e09f91
	https://git.kernel.org/stable/c/18175fe17ae043a0b81e5d511f8817825784c299
	https://git.kernel.org/stable/c/c61760e6940dd4039a7f5e84a6afc9cdbf4d82b6