CVE-2019-12818: NULL Pointer Dereference (CWE-476)
value: An issue was discovered in the Linux kernel before 4.20.15. The nfc_llcp_build_tlv function in net/nfc/llcp_commands.c may return NULL. If the caller does not check for this, it will trigger a NULL pointer dereference. This will cause denial of service. This affects nfc_llcp_build_gb in net/nfc/llcp_core.c.
CWE description: The product dereferences a pointer that it expects to be valid but is NULL.
CVSS v3 base score: 7.5
Published: 2019-06-14T02:29Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: net/nfc/llcp_commands.c, net/nfc/llcp_core.c
Commit date: 2019-02-27 12:47:08 -0800
Commit message: net: nfc: Fix NULL dereference on nfc_llcp_build_tlv fails

KASAN report this:

BUG: KASAN: null-ptr-deref in nfc_llcp_build_gb+0x37f/0x540 [nfc]
Read of size 3 at addr 0000000000000000 by task syz-executor.0/5401

CPU: 0 PID: 5401 Comm: syz-executor.0 Not tainted 5.0.0-rc7+ #45
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xfa/0x1ce lib/dump_stack.c:113
 kasan_report+0x171/0x18d mm/kasan/report.c:321
 memcpy+0x1f/0x50 mm/kasan/common.c:130
 nfc_llcp_build_gb+0x37f/0x540 [nfc]
 nfc_llcp_register_device+0x6eb/0xb50 [nfc]
 nfc_register_device+0x50/0x1d0 [nfc]
 nfcsim_device_new+0x394/0x67d [nfcsim]
 ? 0xffffffffc1080000
 nfcsim_init+0x6b/0x1000 [nfcsim]
 do_one_initcall+0xfa/0x5ca init/main.c:887
 do_init_module+0x204/0x5f6 kernel/module.c:3460
 load_module+0x66b2/0x8570 kernel/module.c:3808
 __do_sys_finit_module+0x238/0x2a0 kernel/module.c:3902
 do_syscall_64+0x147/0x600 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x462e99
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:00007f9cb79dcc58 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000462e99
RDX: 0000000000000000 RSI: 0000000020000280 RDI: 0000000000000003
RBP: 00007f9cb79dcc70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9cb79dd6bc
R13: 00000000004bcefb R14: 00000000006f7030 R15: 0000000000000004

nfc_llcp_build_tlv will return NULL on fails, caller should check it,
otherwise will trigger a NULL dereference.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: eda21f16a5ed ("NFC: Set MIU and RW values from CONNECT and CC LLCP frames")
Fixes: d646960f7986 ("NFC: Initial LLCP support")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Diff: diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c
index 6a196e438b6c..d1fc019e932e 100644
--- a/net/nfc/llcp_commands.c
+++ b/net/nfc/llcp_commands.c
@@ -417,23 +417,35 @@ int nfc_llcp_send_connect(struct nfc_llcp_sock *sock)
 	if (sock->service_name != NULL) {
 		service_name_tlv = nfc_llcp_build_tlv(LLCP_TLV_SN,
 						      sock->service_name,
 						      sock->service_name_len,
 						      &service_name_tlv_length);
+		if (!service_name_tlv) {
+			err = -ENOMEM;
+			goto error_tlv;
+		}
 		size += service_name_tlv_length;
 	}
 
 	/* If the socket parameters are not set, use the local ones */
 	miux = be16_to_cpu(sock->miux) > LLCP_MAX_MIUX ?
 		local->miux : sock->miux;
 	rw = sock->rw > LLCP_MAX_RW ? local->rw : sock->rw;
 
 	miux_tlv = nfc_llcp_build_tlv(LLCP_TLV_MIUX, (u8 *)&miux, 0,
 				      &miux_tlv_length);
+	if (!miux_tlv) {
+		err = -ENOMEM;
+		goto error_tlv;
+	}
 	size += miux_tlv_length;
 
 	rw_tlv = nfc_llcp_build_tlv(LLCP_TLV_RW, &rw, 0, &rw_tlv_length);
+	if (!rw_tlv) {
+		err = -ENOMEM;
+		goto error_tlv;
+	}
 	size += rw_tlv_length;
 
 	pr_debug("SKB size %d SN length %zu\n", size, sock->service_name_len);
 
 	skb = llcp_allocate_pdu(sock, LLCP_PDU_CONNECT, size);
@@ -482,13 +494,21 @@ int nfc_llcp_send_cc(struct nfc_llcp_sock *sock)
 		local->miux : sock->miux;
 	rw = sock->rw > LLCP_MAX_RW ? local->rw : sock->rw;
 
 	miux_tlv = nfc_llcp_build_tlv(LLCP_TLV_MIUX, (u8 *)&miux, 0,
 				      &miux_tlv_length);
+	if (!miux_tlv) {
+		err = -ENOMEM;
+		goto error_tlv;
+	}
 	size += miux_tlv_length;
 
 	rw_tlv = nfc_llcp_build_tlv(LLCP_TLV_RW, &rw, 0, &rw_tlv_length);
+	if (!rw_tlv) {
+		err = -ENOMEM;
+		goto error_tlv;
+	}
 	size += rw_tlv_length;
 
 	skb = llcp_allocate_pdu(sock, LLCP_PDU_CC, size);
 	if (skb == NULL) {
 		err = -ENOMEM;
diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index ef4026a23e80..4fa015208aab 100644
--- a/net/nfc/llcp_core.c
+++ b/net/nfc/llcp_core.c
@@ -530,32 +530,48 @@ static u8 nfc_llcp_reserve_sdp_ssap(struct nfc_llcp_local *local)
 	return LLCP_WKS_NUM_SAP + ssap;
 }
 
 static int nfc_llcp_build_gb(struct nfc_llcp_local *local)
 {
-	u8 *gb_cur, *version_tlv, version, version_length;
-	u8 *lto_tlv, lto_length;
-	u8 *wks_tlv, wks_length;
-	u8 *miux_tlv, miux_length;
+	u8 *gb_cur, version, version_length;
+	u8 lto_length, wks_length, miux_length;
+	u8 *version_tlv = NULL, *lto_tlv = NULL,
+	   *wks_tlv = NULL, *miux_tlv = NULL;
 	__be16 wks = cpu_to_be16(local->local_wks);
 	u8 gb_len = 0;
 	int ret = 0;
 
 	version = LLCP_VERSION_11;
 	version_tlv = nfc_llcp_build_tlv(LLCP_TLV_VERSION, &version,
 					 1, &version_length);
+	if (!version_tlv) {
+		ret = -ENOMEM;
+		goto out;
+	}
 	gb_len += version_length;
 
 	lto_tlv = nfc_llcp_build_tlv(LLCP_TLV_LTO, &local->lto, 1, &lto_length);
+	if (!lto_tlv) {
+		ret = -ENOMEM;
+		goto out;
+	}
 	gb_len += lto_length;
 
 	pr_debug("Local wks 0x%lx\n", local->local_wks);
 	wks_tlv = nfc_llcp_build_tlv(LLCP_TLV_WKS, (u8 *)&wks, 2, &wks_length);
+	if (!wks_tlv) {
+		ret = -ENOMEM;
+		goto out;
+	}
 	gb_len += wks_length;
 
 	miux_tlv = nfc_llcp_build_tlv(LLCP_TLV_MIUX, (u8 *)&local->miux, 0,
 				      &miux_length);
+	if (!miux_tlv) {
+		ret = -ENOMEM;
+		goto out;
+	}
 	gb_len += miux_length;
 
 	gb_len += ARRAY_SIZE(llcp_magic);
 
 	if (gb_len > NFC_MAX_GT_LEN) {

Vulnerable code: 	u8 *gb_cur, *version_tlv, version, version_length;
	u8 *lto_tlv, lto_length;
	u8 *wks_tlv, wks_length;
	u8 *miux_tlv, miux_length;
Fixed code: 		if (!service_name_tlv) {
			err = -ENOMEM;
			goto error_tlv;
		}
	if (!miux_tlv) {
		err = -ENOMEM;
		goto error_tlv;
	}
	if (!rw_tlv) {
		err = -ENOMEM;
		goto error_tlv;
	}
	if (!miux_tlv) {
		err = -ENOMEM;
		goto error_tlv;
	}
	if (!rw_tlv) {
		err = -ENOMEM;
		goto error_tlv;
	}
	u8 *gb_cur, version, version_length;
	u8 lto_length, wks_length, miux_length;
	u8 *version_tlv = NULL, *lto_tlv = NULL,
	   *wks_tlv = NULL, *miux_tlv = NULL;
	if (!version_tlv) {
		ret = -ENOMEM;
		goto out;
	}
	if (!lto_tlv) {
		ret = -ENOMEM;
		goto out;
	}
	if (!wks_tlv) {
		ret = -ENOMEM;
		goto out;
	}
	if (!miux_tlv) {
		ret = -ENOMEM;
		goto out;
	}