netdev - [PATCH net 2/2] net/smc: use memcpy instead of snprintf to avoid out of bounds read

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Date:   Tue, 12 Jan 2021 17:21:22 +0100
From:   Karsten Graul <kgraul@...ux.ibm.com>
To:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Heiko Carstens <hca@...ux.ibm.com>,
        Stefan Raspl <raspl@...ux.ibm.com>, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: [PATCH net 2/2] net/smc: use memcpy instead of snprintf to avoid out of bounds read

From: Guvenc Gulce <guvenc@...ux.ibm.com>

Using snprintf() to convert not null-terminated strings to null
terminated strings may cause out of bounds read in the source string.
Therefore use memcpy() and terminate the target string with a null
afterwards.

Fixes: a3db10efcc4c ("net/smc: Add support for obtaining SMCR device list")
Signed-off-by: Guvenc Gulce <guvenc@...ux.ibm.com>
Signed-off-by: Karsten Graul <kgraul@...ux.ibm.com>
---
 net/smc/smc_core.c | 17 +++++++++++------
 net/smc/smc_ib.c   |  6 +++---
 net/smc/smc_ism.c  |  3 ++-
 3 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index 8d866b4ed8f6..0df85a12651e 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -258,7 +258,8 @@ int smc_nl_get_sys_info(struct sk_buff *skb, struct netlink_callback *cb)
 		smc_ism_get_system_eid(smcd_dev, &seid);
 	mutex_unlock(&smcd_dev_list.mutex);
 	if (seid && smc_ism_is_v2_capable()) {
-		snprintf(smc_seid, sizeof(smc_seid), "%s", seid);
+		memcpy(smc_seid, seid, SMC_MAX_EID_LEN);
+		smc_seid[SMC_MAX_EID_LEN] = 0;
 		if (nla_put_string(skb, SMC_NLA_SYS_SEID, smc_seid))
 			goto errattr;
 	}
@@ -296,7 +297,8 @@ static int smc_nl_fill_lgr(struct smc_link_group *lgr,
 		goto errattr;
 	if (nla_put_u8(skb, SMC_NLA_LGR_R_VLAN_ID, lgr->vlan_id))
 		goto errattr;
-	snprintf(smc_target, sizeof(smc_target), "%s", lgr->pnet_id);
+	memcpy(smc_target, lgr->pnet_id, SMC_MAX_PNETID_LEN);
+	smc_target[SMC_MAX_PNETID_LEN] = 0;
 	if (nla_put_string(skb, SMC_NLA_LGR_R_PNETID, smc_target))
 		goto errattr;
 
@@ -313,7 +315,7 @@ static int smc_nl_fill_lgr_link(struct smc_link_group *lgr,
 				struct sk_buff *skb,
 				struct netlink_callback *cb)
 {
-	char smc_ibname[IB_DEVICE_NAME_MAX + 1];
+	char smc_ibname[IB_DEVICE_NAME_MAX];
 	u8 smc_gid_target[41];
 	struct nlattr *attrs;
 	u32 link_uid = 0;
@@ -462,7 +464,8 @@ static int smc_nl_fill_smcd_lgr(struct smc_link_group *lgr,
 		goto errattr;
 	if (nla_put_u32(skb, SMC_NLA_LGR_D_CHID, smc_ism_get_chid(lgr->smcd)))
 		goto errattr;
-	snprintf(smc_pnet, sizeof(smc_pnet), "%s", lgr->smcd->pnetid);
+	memcpy(smc_pnet, lgr->smcd->pnetid, SMC_MAX_PNETID_LEN);
+	smc_pnet[SMC_MAX_PNETID_LEN] = 0;
 	if (nla_put_string(skb, SMC_NLA_LGR_D_PNETID, smc_pnet))
 		goto errattr;
 
@@ -475,10 +478,12 @@ static int smc_nl_fill_smcd_lgr(struct smc_link_group *lgr,
 		goto errv2attr;
 	if (nla_put_u8(skb, SMC_NLA_LGR_V2_OS, lgr->peer_os))
 		goto errv2attr;
-	snprintf(smc_host, sizeof(smc_host), "%s", lgr->peer_hostname);
+	memcpy(smc_host, lgr->peer_hostname, SMC_MAX_HOSTNAME_LEN);
+	smc_host[SMC_MAX_HOSTNAME_LEN] = 0;
 	if (nla_put_string(skb, SMC_NLA_LGR_V2_PEER_HOST, smc_host))
 		goto errv2attr;
-	snprintf(smc_eid, sizeof(smc_eid), "%s", lgr->negotiated_eid);
+	memcpy(smc_eid, lgr->negotiated_eid, SMC_MAX_EID_LEN);
+	smc_eid[SMC_MAX_EID_LEN] = 0;
 	if (nla_put_string(skb, SMC_NLA_LGR_V2_NEG_EID, smc_eid))
 		goto errv2attr;
 
diff --git a/net/smc/smc_ib.c b/net/smc/smc_ib.c
index ddd7fac98b1d..7d7ba0320d5a 100644
--- a/net/smc/smc_ib.c
+++ b/net/smc/smc_ib.c
@@ -371,8 +371,8 @@ static int smc_nl_handle_dev_port(struct sk_buff *skb,
 	if (nla_put_u8(skb, SMC_NLA_DEV_PORT_PNET_USR,
 		       smcibdev->pnetid_by_user[port]))
 		goto errattr;
-	snprintf(smc_pnet, sizeof(smc_pnet), "%s",
-		 (char *)&smcibdev->pnetid[port]);
+	memcpy(smc_pnet, &smcibdev->pnetid[port], SMC_MAX_PNETID_LEN);
+	smc_pnet[SMC_MAX_PNETID_LEN] = 0;
 	if (nla_put_string(skb, SMC_NLA_DEV_PORT_PNETID, smc_pnet))
 		goto errattr;
 	if (nla_put_u32(skb, SMC_NLA_DEV_PORT_NETDEV,
@@ -414,7 +414,7 @@ static int smc_nl_handle_smcr_dev(struct smc_ib_device *smcibdev,
 				  struct sk_buff *skb,
 				  struct netlink_callback *cb)
 {
-	char smc_ibname[IB_DEVICE_NAME_MAX + 1];
+	char smc_ibname[IB_DEVICE_NAME_MAX];
 	struct smc_pci_dev smc_pci_dev;
 	struct pci_dev *pci_dev;
 	unsigned char is_crit;
diff --git a/net/smc/smc_ism.c b/net/smc/smc_ism.c
index 524ef64a191a..9c6e95882553 100644
--- a/net/smc/smc_ism.c
+++ b/net/smc/smc_ism.c
@@ -250,7 +250,8 @@ static int smc_nl_handle_smcd_dev(struct smcd_dev *smcd,
 		goto errattr;
 	if (nla_put_u8(skb, SMC_NLA_DEV_PORT_PNET_USR, smcd->pnetid_by_user))
 		goto errportattr;
-	snprintf(smc_pnet, sizeof(smc_pnet), "%s", smcd->pnetid);
+	memcpy(smc_pnet, smcd->pnetid, SMC_MAX_PNETID_LEN);
+	smc_pnet[SMC_MAX_PNETID_LEN] = 0;
 	if (nla_put_string(skb, SMC_NLA_DEV_PORT_PNETID, smc_pnet))
 		goto errportattr;
 
-- 
2.17.1