From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Jamin Mc <jaminmc@gmail.com>,
	=?UTF-8?q?Fabian=20Gr=C3=BCnbichler?= <f.gruenbichler@proxmox.com>,
	John Johansen <john.johansen@canonical.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18 563/641] apparmor: fix NULL pointer dereference in __unix_needs_revalidation
Date: Tue, 24 Feb 2026 17:24:49 -0800
Message-ID: <20260225012402.164160645@linuxfoundation.org>
In-Reply-To: <20260225012348.915798704@linuxfoundation.org>
References: <20260225012348.915798704@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: System Administrator <root@localhost>

[ Upstream commit e2938ad00b21340c0362562dfedd7cfec0554d67 ]

When receiving file descriptors via SCM_RIGHTS, both the socket pointer
and the socket's sk pointer can be NULL during socket setup or teardown,
causing NULL pointer dereferences in __unix_needs_revalidation().

This is a regression in AppArmor 5.0.0 (kernel 6.17+) where the new
__unix_needs_revalidation() function was added without proper NULL checks.

The crash manifests as:
  BUG: kernel NULL pointer dereference, address: 0x0000000000000018
  RIP: aa_file_perm+0xb7/0x3b0 (or +0xbe/0x3b0, +0xc0/0x3e0)
  Call Trace:
   apparmor_file_receive+0x42/0x80
   security_file_receive+0x2e/0x50
   receive_fd+0x1d/0xf0
   scm_detach_fds+0xad/0x1c0

The function dereferences sock->sk->sk_family without checking if either
sock or sock->sk is NULL first.

Add NULL checks for both sock and sock->sk before accessing sk_family.

Fixes: 88fec3526e841 ("apparmor: make sure unix socket labeling is correctly updated.")
Reported-by: Jamin Mc <jaminmc@gmail.com>
Closes: https://bugzilla.proxmox.com/show_bug.cgi?id=7083
Closes: https://gitlab.com/apparmor/apparmor/-/issues/568
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Signed-off-by: System Administrator <root@localhost>
Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 security/apparmor/file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/security/apparmor/file.c b/security/apparmor/file.c
index c758204028780..919dbbbc87ab6 100644
--- a/security/apparmor/file.c
+++ b/security/apparmor/file.c
@@ -578,6 +578,9 @@ static bool __unix_needs_revalidation(struct file *file, struct aa_label *label,
 		return false;
 	if (request & NET_PEER_MASK)
 		return false;
+	/* sock and sock->sk can be NULL for sockets being set up or torn down */
+	if (!sock || !sock->sk)
+		return false;
 	if (sock->sk->sk_family == PF_UNIX) {
 		struct aa_sk_ctx *ctx = aa_sock(sock->sk);
 
-- 
2.51.0