[PATCH v2 net 0/2] af_unix: Fix a NULL deref in sk_diag_dump_uid().

[PATCH v2 net 0/2] af_unix: Fix a NULL deref in sk_diag_dump_uid().

[Kuniyuki Iwashima]

The first patch fixes a NULL deref when we dump a AF_UNIX socket's UID,
and the second patch adds a repro/test for such a case.


Changes:
  v2:
    * Get user_ns from NETLINK_CB(in_skb).sk.
    * Add test.

  v1: https://lore.kernel.org/netdev/20221122205811.20910-1-kuniyu@amazon.com/


Kuniyuki Iwashima (2):
  af_unix: Get user_ns from in_skb in unix_diag_get_exact().
  af_unix: Add test for sock_diag and UDIAG_SHOW_UID.

 net/unix/diag.c                               |  20 +-
 tools/testing/selftests/net/.gitignore        |   1 +
 tools/testing/selftests/net/af_unix/Makefile  |   2 +-
 .../testing/selftests/net/af_unix/diag_uid.c  | 178 ++++++++++++++++++
 4 files changed, 192 insertions(+), 9 deletions(-)
 create mode 100644 tools/testing/selftests/net/af_unix/diag_uid.c

-- 
2.30.2

[PATCH v2 net 1/2] af_unix: Get user_ns from in_skb in unix_diag_get_exact().

[Kuniyuki Iwashima]

Wei Chen reported a NULL deref in sk_user_ns() [0][1], and Paolo diagnosed
the root cause: in unix_diag_get_exact(), the newly allocated skb does not
have sk. [2]

We must get the user_ns from the NETLINK_CB(in_skb).sk and pass it to
sk_diag_fill().

[0]:
BUG: kernel NULL pointer dereference, address: 0000000000000270
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 12bbce067 P4D 12bbce067 PUD 12bc40067 PMD 0
Oops: 0000 [#1] PREEMPT SMP
CPU: 0 PID: 27942 Comm: syz-executor.0 Not tainted 6.1.0-rc5-next-20221118 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014
RIP: 0010:sk_user_ns include/net/sock.h:920 [inline]
RIP: 0010:sk_diag_dump_uid net/unix/diag.c:119 [inline]
RIP: 0010:sk_diag_fill+0x77d/0x890 net/unix/diag.c:170
Code: 89 ef e8 66 d4 2d fd c7 44 24 40 00 00 00 00 49 8d 7c 24 18 e8
54 d7 2d fd 49 8b 5c 24 18 48 8d bb 70 02 00 00 e8 43 d7 2d fd <48> 8b
9b 70 02 00 00 48 8d 7b 10 e8 33 d7 2d fd 48 8b 5b 10 48 8d
RSP: 0018:ffffc90000d67968 EFLAGS: 00010246
RAX: ffff88812badaa48 RBX: 0000000000000000 RCX: ffffffff840d481d
RDX: 0000000000000465 RSI: 0000000000000000 RDI: 0000000000000270
RBP: ffffc90000d679a8 R08: 0000000000000277 R09: 0000000000000000
R10: 0001ffffffffffff R11: 0001c90000d679a8 R12: ffff88812ac03800
R13: ffff88812c87c400 R14: ffff88812ae42210 R15: ffff888103026940
FS:  00007f08b4e6f700(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000270 CR3: 000000012c58b000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 unix_diag_get_exact net/unix/diag.c:285 [inline]
 unix_diag_handler_dump+0x3f9/0x500 net/unix/diag.c:317
 __sock_diag_cmd net/core/sock_diag.c:235 [inline]
 sock_diag_rcv_msg+0x237/0x250 net/core/sock_diag.c:266
 netlink_rcv_skb+0x13e/0x250 net/netlink/af_netlink.c:2564
 sock_diag_rcv+0x24/0x40 net/core/sock_diag.c:277
 netlink_unicast_kernel net/netlink/af_netlink.c:1330 [inline]
 netlink_unicast+0x5e9/0x6b0 net/netlink/af_netlink.c:1356
 netlink_sendmsg+0x739/0x860 net/netlink/af_netlink.c:1932
 sock_sendmsg_nosec net/socket.c:714 [inline]
 sock_sendmsg net/socket.c:734 [inline]
 ____sys_sendmsg+0x38f/0x500 net/socket.c:2476
 ___sys_sendmsg net/socket.c:2530 [inline]
 __sys_sendmsg+0x197/0x230 net/socket.c:2559
 __do_sys_sendmsg net/socket.c:2568 [inline]
 __se_sys_sendmsg net/socket.c:2566 [inline]
 __x64_sys_sendmsg+0x42/0x50 net/socket.c:2566
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x4697f9
Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48
89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f08b4e6ec48 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000077bf80 RCX: 00000000004697f9
RDX: 0000000000000000 RSI: 00000000200001c0 RDI: 0000000000000003
RBP: 00000000004d29e9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000077bf80
R13: 0000000000000000 R14: 000000000077bf80 R15: 00007ffdb36bc6c0
 </TASK>
Modules linked in:
CR2: 0000000000000270

[1]: https://lore.kernel.org/netdev/CAO4mrfdvyjFpokhNsiwZiP-wpdSD0AStcJwfKcKQdAALQ9_2Qw@mail.gmail.com/
[2]: https://lore.kernel.org/netdev/e04315e7c90d9a75613f3993c2baf2d344eef7eb.camel@redhat.com/

Fixes: cae9910e7344 ("net: Add UNIX_DIAG_UID to Netlink UNIX socket diagnostics.")
Reported-by: syzbot <syzkaller@googlegroups.com>
Reported-by: Wei Chen <harperchen1110@gmail.com>
Diagnosed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 net/unix/diag.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/net/unix/diag.c b/net/unix/diag.c
index 105f522a89fe..616b55c5b890 100644
--- a/net/unix/diag.c
+++ b/net/unix/diag.c
@@ -114,14 +114,16 @@ static int sk_diag_show_rqlen(struct sock *sk, struct sk_buff *nlskb)
 	return nla_put(nlskb, UNIX_DIAG_RQLEN, sizeof(rql), &rql);
 }
 
-static int sk_diag_dump_uid(struct sock *sk, struct sk_buff *nlskb)
+static int sk_diag_dump_uid(struct sock *sk, struct sk_buff *nlskb,
+			    struct user_namespace *user_ns)
 {
-	uid_t uid = from_kuid_munged(sk_user_ns(nlskb->sk), sock_i_uid(sk));
+	uid_t uid = from_kuid_munged(user_ns, sock_i_uid(sk));
 	return nla_put(nlskb, UNIX_DIAG_UID, sizeof(uid_t), &uid);
 }
 
 static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_req *req,
-		u32 portid, u32 seq, u32 flags, int sk_ino)
+			struct user_namespace *user_ns,
+			u32 portid, u32 seq, u32 flags, int sk_ino)
 {
 	struct nlmsghdr *nlh;
 	struct unix_diag_msg *rep;
@@ -167,7 +169,7 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
 		goto out_nlmsg_trim;
 
 	if ((req->udiag_show & UDIAG_SHOW_UID) &&
-	    sk_diag_dump_uid(sk, skb))
+	    sk_diag_dump_uid(sk, skb, user_ns))
 		goto out_nlmsg_trim;
 
 	nlmsg_end(skb, nlh);
@@ -179,7 +181,8 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
 }
 
 static int sk_diag_dump(struct sock *sk, struct sk_buff *skb, struct unix_diag_req *req,
-		u32 portid, u32 seq, u32 flags)
+			struct user_namespace *user_ns,
+			u32 portid, u32 seq, u32 flags)
 {
 	int sk_ino;
 
@@ -190,7 +193,7 @@ static int sk_diag_dump(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
 	if (!sk_ino)
 		return 0;
 
-	return sk_diag_fill(sk, skb, req, portid, seq, flags, sk_ino);
+	return sk_diag_fill(sk, skb, req, user_ns, portid, seq, flags, sk_ino);
 }
 
 static int unix_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
@@ -214,7 +217,7 @@ static int unix_diag_dump(struct sk_buff *skb, struct netlink_callback *cb)
 				goto next;
 			if (!(req->udiag_states & (1 << sk->sk_state)))
 				goto next;
-			if (sk_diag_dump(sk, skb, req,
+			if (sk_diag_dump(sk, skb, req, sk_user_ns(skb->sk),
 					 NETLINK_CB(cb->skb).portid,
 					 cb->nlh->nlmsg_seq,
 					 NLM_F_MULTI) < 0) {
@@ -282,7 +285,8 @@ static int unix_diag_get_exact(struct sk_buff *in_skb,
 	if (!rep)
 		goto out;
 
-	err = sk_diag_fill(sk, rep, req, NETLINK_CB(in_skb).portid,
+	err = sk_diag_fill(sk, rep, req, sk_user_ns(NETLINK_CB(in_skb).sk),
+			   NETLINK_CB(in_skb).portid,
 			   nlh->nlmsg_seq, 0, req->udiag_ino);
 	if (err < 0) {
 		nlmsg_free(rep);
-- 
2.30.2

[PATCH v2 net 2/2] af_unix: Add test for sock_diag and UDIAG_SHOW_UID.

[Kuniyuki Iwashima]

The test prog dumps a single AF_UNIX socket's UID with and without
unshare(CLONE_NEWUSER) and checks if it matches the result of getuid().

Without the preceding patch, the test prog is killed by a NULL deref
in sk_diag_dump_uid().

  # ./diag_uid
  TAP version 13
  1..2
  # Starting 2 tests from 3 test cases.
  #  RUN           diag_uid.uid.1 ...
  BUG: kernel NULL pointer dereference, address: 0000000000000270
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 105212067 P4D 105212067 PUD 1051fe067 PMD 0
  Oops: 0000 [#1] PREEMPT SMP NOPTI
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.amzn2022.0.1 04/01/2014
  RIP: 0010:sk_diag_fill (./include/net/sock.h:920 net/unix/diag.c:119 net/unix/diag.c:170)
  ...
  # 1: Test terminated unexpectedly by signal 9
  #          FAIL  diag_uid.uid.1
  not ok 1 diag_uid.uid.1
  #  RUN           diag_uid.uid_unshare.1 ...
  # 1: Test terminated by timeout
  #          FAIL  diag_uid.uid_unshare.1
  not ok 2 diag_uid.uid_unshare.1
  # FAILED: 0 / 2 tests passed.
  # Totals: pass:0 fail:2 xfail:0 xpass:0 skip:0 error:0

With the patch, the test succeeds.

  # ./diag_uid
  TAP version 13
  1..2
  # Starting 2 tests from 3 test cases.
  #  RUN           diag_uid.uid.1 ...
  #            OK  diag_uid.uid.1
  ok 1 diag_uid.uid.1
  #  RUN           diag_uid.uid_unshare.1 ...
  #            OK  diag_uid.uid_unshare.1
  ok 2 diag_uid.uid_unshare.1
  # PASSED: 2 / 2 tests passed.
  # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 tools/testing/selftests/net/.gitignore        |   1 +
 tools/testing/selftests/net/af_unix/Makefile  |   2 +-
 .../testing/selftests/net/af_unix/diag_uid.c  | 178 ++++++++++++++++++
 3 files changed, 180 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/net/af_unix/diag_uid.c

diff --git a/tools/testing/selftests/net/.gitignore b/tools/testing/selftests/net/.gitignore
index 3d7adee7a3e6..ff8fe93f679c 100644
--- a/tools/testing/selftests/net/.gitignore
+++ b/tools/testing/selftests/net/.gitignore
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 bind_bhash
 cmsg_sender
+diag_uid
 fin_ack_lat
 gro
 hwtstamp_config
diff --git a/tools/testing/selftests/net/af_unix/Makefile b/tools/testing/selftests/net/af_unix/Makefile
index 969620ae9928..1e4b397cece6 100644
--- a/tools/testing/selftests/net/af_unix/Makefile
+++ b/tools/testing/selftests/net/af_unix/Makefile
@@ -1,3 +1,3 @@
-TEST_GEN_PROGS := test_unix_oob unix_connect
+TEST_GEN_PROGS := diag_uid test_unix_oob unix_connect
 
 include ../../lib.mk
diff --git a/tools/testing/selftests/net/af_unix/diag_uid.c b/tools/testing/selftests/net/af_unix/diag_uid.c
new file mode 100644
index 000000000000..5b88f7129fea
--- /dev/null
+++ b/tools/testing/selftests/net/af_unix/diag_uid.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright Amazon.com Inc. or its affiliates. */
+
+#define _GNU_SOURCE
+#include <sched.h>
+
+#include <unistd.h>
+#include <linux/netlink.h>
+#include <linux/rtnetlink.h>
+#include <linux/sock_diag.h>
+#include <linux/unix_diag.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/un.h>
+
+#include "../../kselftest_harness.h"
+
+FIXTURE(diag_uid)
+{
+	int netlink_fd;
+	int unix_fd;
+	__u32 inode;
+	__u64 cookie;
+};
+
+FIXTURE_VARIANT(diag_uid)
+{
+	int unshare;
+	int udiag_show;
+};
+
+FIXTURE_VARIANT_ADD(diag_uid, uid)
+{
+	.unshare = 0,
+	.udiag_show = UDIAG_SHOW_UID
+};
+
+FIXTURE_VARIANT_ADD(diag_uid, uid_unshare)
+{
+	.unshare = CLONE_NEWUSER,
+	.udiag_show = UDIAG_SHOW_UID
+};
+
+FIXTURE_SETUP(diag_uid)
+{
+	struct stat file_stat;
+	socklen_t optlen;
+	int ret;
+
+	if (variant->unshare)
+		ASSERT_EQ(unshare(variant->unshare), 0);
+
+	self->netlink_fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG);
+	ASSERT_NE(self->netlink_fd, -1);
+
+	self->unix_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	ASSERT_NE(self->unix_fd, -1);
+
+	ret = fstat(self->unix_fd, &file_stat);
+	ASSERT_EQ(ret, 0);
+
+	self->inode = file_stat.st_ino;
+
+	optlen = sizeof(self->cookie);
+	ret = getsockopt(self->unix_fd, SOL_SOCKET, SO_COOKIE, &self->cookie, &optlen);
+	ASSERT_EQ(ret, 0);
+}
+
+FIXTURE_TEARDOWN(diag_uid)
+{
+	close(self->netlink_fd);
+	close(self->unix_fd);
+}
+
+int send_request(struct __test_metadata *_metadata,
+		 FIXTURE_DATA(diag_uid) *self,
+		 const FIXTURE_VARIANT(diag_uid) *variant)
+{
+	struct {
+		struct nlmsghdr nlh;
+		struct unix_diag_req udr;
+	} req = {
+		.nlh = {
+			.nlmsg_len = sizeof(req),
+			.nlmsg_type = SOCK_DIAG_BY_FAMILY,
+			.nlmsg_flags = NLM_F_REQUEST
+		},
+		.udr = {
+			.sdiag_family = AF_UNIX,
+			.udiag_ino = self->inode,
+			.udiag_cookie = {
+				(__u32)self->cookie,
+				(__u32)(self->cookie >> 32)
+			},
+			.udiag_show = variant->udiag_show
+		}
+	};
+	struct sockaddr_nl nladdr = {
+		.nl_family = AF_NETLINK
+	};
+	struct iovec iov = {
+		.iov_base = &req,
+		.iov_len = sizeof(req)
+	};
+	struct msghdr msg = {
+		.msg_name = &nladdr,
+		.msg_namelen = sizeof(nladdr),
+		.msg_iov = &iov,
+		.msg_iovlen = 1
+	};
+
+	return sendmsg(self->netlink_fd, &msg, 0);
+}
+
+void render_response(struct __test_metadata *_metadata,
+		     struct unix_diag_req *udr, __u32 len)
+{
+	unsigned int rta_len = len - NLMSG_LENGTH(sizeof(*udr));
+	struct rtattr *attr;
+	uid_t uid;
+
+	ASSERT_GT(len, sizeof(*udr));
+	ASSERT_EQ(udr->sdiag_family, AF_UNIX);
+
+	attr = (struct rtattr *)(udr + 1);
+	ASSERT_NE(RTA_OK(attr, rta_len), 0);
+	ASSERT_EQ(attr->rta_type, UNIX_DIAG_UID);
+
+	uid = *(uid_t *)RTA_DATA(attr);
+	ASSERT_EQ(uid, getuid());
+}
+
+void receive_response(struct __test_metadata *_metadata,
+		      FIXTURE_DATA(diag_uid) *self)
+{
+	long buf[8192 / sizeof(long)];
+	struct sockaddr_nl nladdr = {
+		.nl_family = AF_NETLINK
+	};
+	struct iovec iov = {
+		.iov_base = buf,
+		.iov_len = sizeof(buf)
+	};
+	struct msghdr msg = {
+		.msg_name = &nladdr,
+		.msg_namelen = sizeof(nladdr),
+		.msg_iov = &iov,
+		.msg_iovlen = 1
+	};
+	struct unix_diag_req *udr;
+	struct nlmsghdr *nlh;
+	int ret;
+
+	ret = recvmsg(self->netlink_fd, &msg, 0);
+	ASSERT_GT(ret, 0);
+
+	nlh = (struct nlmsghdr *)buf;
+	ASSERT_NE(NLMSG_OK(nlh, ret), 0);
+	ASSERT_EQ(nlh->nlmsg_type, SOCK_DIAG_BY_FAMILY);
+
+	render_response(_metadata, NLMSG_DATA(nlh), nlh->nlmsg_len);
+
+	nlh = NLMSG_NEXT(nlh, ret);
+	ASSERT_EQ(NLMSG_OK(nlh, ret), 0);
+}
+
+TEST_F(diag_uid, 1)
+{
+	int ret;
+
+	ret = send_request(_metadata, self, variant);
+	ASSERT_GT(ret, 0);
+
+	receive_response(_metadata, self);
+}
+
+TEST_HARNESS_MAIN
-- 
2.30.2

Re: [PATCH v2 net 0/2] af_unix: Fix a NULL deref in sk_diag_dump_uid().

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (master)
by Paolo Abeni <pabeni@redhat.com>:

On Sun, 27 Nov 2022 10:24:10 +0900 you wrote:
> The first patch fixes a NULL deref when we dump a AF_UNIX socket's UID,
> and the second patch adds a repro/test for such a case.
> 
> 
> Changes:
>   v2:
>     * Get user_ns from NETLINK_CB(in_skb).sk.
>     * Add test.
> 
> [...]

Here is the summary with links:
  - [v2,net,1/2] af_unix: Get user_ns from in_skb in unix_diag_get_exact().
    https://git.kernel.org/netdev/net/c/b3abe42e9490
  - [v2,net,2/2] af_unix: Add test for sock_diag and UDIAG_SHOW_UID.
    https://git.kernel.org/netdev/net/c/ac011361bd4f

You are awesome, thank you!
-- 
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