diff mbox series

[25/27] NET: Add SO_PEERCONTEXT for multiple LSMs

Message ID 20190726233923.2570-26-casey@schaufler-ca.com (mailing list archive)
State Superseded
Headers show
Series LSM: Module stacking for AppArmor | expand

Commit Message

Casey Schaufler July 26, 2019, 11:39 p.m. UTC 
The getsockopt SO_PEERSEC provides the LSM based security
information for a single module, but for reasons of backward
compatibility cannot include the information for multiple
modules. A new option SO_PEERCONTEXT is added to report the
security "context" of multiple modules using a "compound" format

	lsm1\0value\0lsm2\0value\0

This is expected to be used by system services, including dbus-daemon.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
---
 arch/alpha/include/uapi/asm/socket.h  |  1 +
 arch/mips/include/uapi/asm/socket.h   |  1 +
 arch/parisc/include/uapi/asm/socket.h |  1 +
 arch/sparc/include/uapi/asm/socket.h  |  1 +
 include/linux/lsm_hooks.h             |  9 ++-
 include/linux/security.h              | 10 ++-
 include/uapi/asm-generic/socket.h     |  1 +
 net/core/sock.c                       |  7 +-
 security/apparmor/lsm.c               | 20 ++----
 security/security.c                   | 94 ++++++++++++++++++++++++---
 security/selinux/hooks.c              | 20 ++----
 security/smack/smack_lsm.c            | 31 ++++-----
 12 files changed, 134 insertions(+), 62 deletions(-)

Comments

Simon McVittie July 29, 2019, 1 p.m. UTC | #1 
On Fri, 26 Jul 2019 at 16:39:21 -0700, Casey Schaufler wrote:
> A new option SO_PEERCONTEXT is added to report the
> security "context" of multiple modules using a "compound" format
> 
> 	lsm1\0value\0lsm2\0value\0

> +		/*
> +		 * A compound context, in the form lsm='value'[,lsm='value']...
> +		 */

Presumably the commit message (and the implementation) means the comment
is out of date?

> +			/*
> +			 * Don't propogate trailing nul bytes.
> +			 */
> +			clen = strnlen(cp, clen) + 1;
> +			tlen = llen + clen;
...
> +			memcpy(tp + finallen + llen, cp, clen);

This assumes that cp points to a '\0'-terminated string, with the '\0'
either inside the span of memory cp[clen]..cp[clen-1], or at cp[clen]
(which is just outside the range that is obviously safe to access).
Is that assumption robust? If an LSM that worked with length-counted
("Pascal") strings internally would be allowed to fill the buffer with
nonzero bytes and not place a '\0' immediately after it, then it would
be necessary to insert the NUL explicitly:

    clen = strnlen(cp, clen);
    tlen = llen + clen + 1;
    ...
    memcpy(tp + finallen + llen, cp, clen);
    tp[finallen + llen + clen] = '\0';

Thanks,
    smcv
Casey Schaufler July 29, 2019, 3:04 p.m. UTC | #2 
On 7/29/2019 6:00 AM, Simon McVittie wrote:
> On Fri, 26 Jul 2019 at 16:39:21 -0700, Casey Schaufler wrote:
>> A new option SO_PEERCONTEXT is added to report the
>> security "context" of multiple modules using a "compound" format
>>
>> 	lsm1\0value\0lsm2\0value\0
>> +		/*
>> +		 * A compound context, in the form lsm='value'[,lsm='value']...
>> +		 */
> Presumably the commit message (and the implementation) means the comment
> is out of date?

Yup. The curse of incremental development.


>> +			/*
>> +			 * Don't propogate trailing nul bytes.
>> +			 */
>> +			clen = strnlen(cp, clen) + 1;
>> +			tlen = llen + clen;
> ...
>> +			memcpy(tp + finallen + llen, cp, clen);
> This assumes that cp points to a '\0'-terminated string, with the '\0'
> either inside the span of memory cp[clen]..cp[clen-1], or at cp[clen]
> (which is just outside the range that is obviously safe to access).
> Is that assumption robust?

James Morris, the security subsystem maintainer, says:

	"Security labels are strings, so this is implied."

>  If an LSM that worked with length-counted
> ("Pascal") strings internally would be allowed to fill the buffer with
> nonzero bytes and not place a '\0' immediately after it, then it would
> be necessary to insert the NUL explicitly:

True enough. I could use an embedded length format:

	[<lsmname\0><valuesize-u16><value>]...

but as James is willing to assert that security labels are strings
I don't think we need to go that far.

>
>     clen = strnlen(cp, clen);
>     tlen = llen + clen + 1;
>     ...
>     memcpy(tp + finallen + llen, cp, clen);
>     tp[finallen + llen + clen] = '\0';
>
> Thanks,
>     smcv
diff mbox series

Patch

diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index 976e89b116e5..019e5fa8bcda 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -121,6 +121,7 @@ 
 
 #define SO_RCVTIMEO_NEW         66
 #define SO_SNDTIMEO_NEW         67
+#define SO_PEERCONTEXT          68
 
 #if !defined(__KERNEL__)
 
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index d41765cfbc6e..df8d984d76ed 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -132,6 +132,7 @@ 
 
 #define SO_RCVTIMEO_NEW         66
 #define SO_SNDTIMEO_NEW         67
+#define SO_PEERCONTEXT          68
 
 #if !defined(__KERNEL__)
 
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index 66c5dd245ac7..9ae358309f46 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -113,6 +113,7 @@ 
 
 #define SO_RCVTIMEO_NEW         0x4040
 #define SO_SNDTIMEO_NEW         0x4041
+#define SO_PEERCONTEXT          0x4042
 
 #if !defined(__KERNEL__)
 
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 9265a9eece15..e8a53ef65210 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -114,6 +114,7 @@ 
 
 #define SO_RCVTIMEO_NEW          0x0044
 #define SO_SNDTIMEO_NEW          0x0045
+#define SO_PEERCONTEXT           0x0046
 
 #if !defined(__KERNEL__)
 
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 33e5ab4af9f8..b0f788bf82b6 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -864,8 +864,8 @@ 
  *	SO_GETPEERSEC.  For tcp sockets this can be meaningful if the
  *	socket is associated with an ipsec SA.
  *	@sock is the local socket.
- *	@optval userspace memory where the security state is to be copied.
- *	@optlen userspace int where the module should copy the actual length
+ *	@optval memory where the security state is to be copied.
+ *	@optlen int where the module should copy the actual length
  *	of the security state.
  *	@len as input is the maximum length to copy to userspace provided
  *	by the caller.
@@ -1697,9 +1697,8 @@  union security_list_options {
 	int (*socket_setsockopt)(struct socket *sock, int level, int optname);
 	int (*socket_shutdown)(struct socket *sock, int how);
 	int (*socket_sock_rcv_skb)(struct sock *sk, struct sk_buff *skb);
-	int (*socket_getpeersec_stream)(struct socket *sock,
-					char __user *optval,
-					int __user *optlen, unsigned len);
+	int (*socket_getpeersec_stream)(struct socket *sock, char **optval,
+					int *optlen, unsigned len);
 	int (*socket_getpeersec_dgram)(struct socket *sock,
 					struct sk_buff *skb, u32 *secid);
 	int (*sk_alloc_security)(struct sock *sk, int family, gfp_t priority);
diff --git a/include/linux/security.h b/include/linux/security.h
index 12f6d5fcbf6a..0665a27a2891 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -130,6 +130,7 @@  struct lsmblob {
 #define LSMBLOB_NOT_NEEDED	-3	/* Slot not requested */
 #define LSMBLOB_DISPLAY		-4	/* Use the "display" slot */
 #define LSMBLOB_FIRST		-5	/* Use the default "display" slot */
+#define LSMBLOB_COMPOUND	-6	/* A compound "display" */
 
 /**
  * lsmblob_init - initialize an lsmblob structure.
@@ -1324,7 +1325,8 @@  int security_socket_setsockopt(struct socket *sock, int level, int optname);
 int security_socket_shutdown(struct socket *sock, int how);
 int security_sock_rcv_skb(struct sock *sk, struct sk_buff *skb);
 int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
-				      int __user *optlen, unsigned len);
+				      int __user *optlen, unsigned len,
+				      int display);
 int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb,
 				     struct lsmblob *blob);
 int security_sk_alloc(struct sock *sk, int family, gfp_t priority);
@@ -1458,8 +1460,10 @@  static inline int security_sock_rcv_skb(struct sock *sk,
 	return 0;
 }
 
-static inline int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
-						    int __user *optlen, unsigned len)
+static inline int security_socket_getpeersec_stream(struct socket *sock,
+						    char __user *optval,
+						    int __user *optlen,
+						    unsigned len, int display)
 {
 	return -ENOPROTOOPT;
 }
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 8c1391c89171..b38d080c2802 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -116,6 +116,7 @@ 
 
 #define SO_RCVTIMEO_NEW         66
 #define SO_SNDTIMEO_NEW         67
+#define SO_PEERCONTEXT          68
 
 #if !defined(__KERNEL__)
 
diff --git a/net/core/sock.c b/net/core/sock.c
index 782343bb925b..b0955a34167c 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1412,7 +1412,12 @@  int sock_getsockopt(struct socket *sock, int level, int optname,
 		break;
 
 	case SO_PEERSEC:
-		return security_socket_getpeersec_stream(sock, optval, optlen, len);
+		return security_socket_getpeersec_stream(sock, optval, optlen,
+							 len, LSMBLOB_DISPLAY);
+
+	case SO_PEERCONTEXT:
+		return security_socket_getpeersec_stream(sock, optval, optlen,
+							 len, LSMBLOB_COMPOUND);
 
 	case SO_MARK:
 		v.val = sk->sk_mark;
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index ec2e39aa9a84..5d25959610f9 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1037,10 +1037,8 @@  static struct aa_label *sk_peer_label(struct sock *sk)
  *
  * Note: for tcp only valid if using ipsec or cipso on lan
  */
-static int apparmor_socket_getpeersec_stream(struct socket *sock,
-					     char __user *optval,
-					     int __user *optlen,
-					     unsigned int len)
+static int apparmor_socket_getpeersec_stream(struct socket *sock, char **optval,
+					     int *optlen, unsigned int len)
 {
 	char *name;
 	int slen, error = 0;
@@ -1060,17 +1058,11 @@  static int apparmor_socket_getpeersec_stream(struct socket *sock,
 	if (slen < 0) {
 		error = -ENOMEM;
 	} else {
-		if (slen > len) {
+		if (slen > len)
 			error = -ERANGE;
-		} else if (copy_to_user(optval, name, slen)) {
-			error = -EFAULT;
-			goto out;
-		}
-		if (put_user(slen, optlen))
-			error = -EFAULT;
-out:
-		kfree(name);
-
+		else
+			*optval = name;
+		*optlen = slen;
 	}
 
 done:
diff --git a/security/security.c b/security/security.c
index 9e5e3ebd169d..5551c146c035 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2126,8 +2126,8 @@  int security_setprocattr(const char *lsm, const char *name, void *value,
 	hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) {
 		if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
 			continue;
-		if (lsm == NULL && *display != LSMBLOB_INVALID &&
-		    *display != hp->lsmid->slot)
+		if (lsm == NULL && display != NULL &&
+		    *display != LSMBLOB_INVALID && *display != hp->lsmid->slot)
 			continue;
 		return hp->hook.setprocattr(name, value, size);
 	}
@@ -2351,17 +2351,91 @@  int security_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 EXPORT_SYMBOL(security_sock_rcv_skb);
 
 int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
-				      int __user *optlen, unsigned len)
+				      int __user *optlen, unsigned len,
+				      int display)
 {
-	int display = lsm_task_display(current);
 	struct security_hook_list *hp;
+	char *final = NULL;
+	char *cp;
+	char *tp;
+	int rc = 0;
+	unsigned finallen = 0;
+	unsigned llen;
+	unsigned clen = 0;
+	unsigned tlen;
+
+	switch (display) {
+	case LSMBLOB_DISPLAY:
+		rc = -ENOPROTOOPT;
+		display = lsm_task_display(current);
+		hlist_for_each_entry(hp,
+				&security_hook_heads.socket_getpeersec_stream,
+				list)
+			if (display == LSMBLOB_INVALID ||
+			    display == hp->lsmid->slot) {
+				rc = hp->hook.socket_getpeersec_stream(sock,
+							&final, &finallen, len);
+				break;
+			}
+		break;
+	case LSMBLOB_COMPOUND:
+		/*
+		 * A compound context, in the form lsm='value'[,lsm='value']...
+		 */
+		hlist_for_each_entry(hp,
+				&security_hook_heads.socket_getpeersec_stream,
+				list) {
+			rc = hp->hook.socket_getpeersec_stream(sock, &cp, &clen,
+							       len);
+			if (rc == -EINVAL || rc == -ENOPROTOOPT) {
+				rc = 0;
+				continue;
+			}
+			if (rc) {
+				kfree(final);
+				return rc;
+			}
+			/*
+			 * Don't propogate trailing nul bytes.
+			 */
+			clen = strnlen(cp, clen) + 1;
+			llen = strlen(hp->lsmid->lsm) + 1;
+			tlen = llen + clen;
+			if (final)
+				tlen += finallen;
+			tp = kzalloc(tlen, GFP_KERNEL);
+			if (tp == NULL) {
+				kfree(cp);
+				kfree(final);
+				return -ENOMEM;
+			}
+			if (final)
+				memcpy(tp, final, finallen);
+			memcpy(tp + finallen, hp->lsmid->lsm, llen);
+			memcpy(tp + finallen + llen, cp, clen);
+			kfree(cp);
+			if (final)
+				kfree(final);
+			final = tp;
+			finallen = tlen;
+		}
+		if (final == NULL)
+			return -EINVAL;
+		break;
+	default:
+		return -EINVAL;
+	}
 
-	hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream,
-			     list)
-		if (display == LSMBLOB_INVALID || display == hp->lsmid->slot)
-			return hp->hook.socket_getpeersec_stream(sock, optval,
-								 optlen, len);
-	return -ENOPROTOOPT;
+	if (finallen > len)
+		rc = -ERANGE;
+	else if (copy_to_user(optval, final, finallen))
+		rc = -EFAULT;
+
+	if (put_user(finallen, optlen))
+		rc = -EFAULT;
+
+	kfree(final);
+	return rc;
 }
 
 int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb,
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index fcad2e3432d2..5e7d61754798 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4923,10 +4923,8 @@  static int selinux_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	return err;
 }
 
-static int selinux_socket_getpeersec_stream(struct socket *sock,
-					    char __user *optval,
-					    int __user *optlen,
-					    unsigned int len)
+static int selinux_socket_getpeersec_stream(struct socket *sock, char **optval,
+					    int *optlen, unsigned int len)
 {
 	int err = 0;
 	char *scontext;
@@ -4946,18 +4944,12 @@  static int selinux_socket_getpeersec_stream(struct socket *sock,
 	if (err)
 		return err;
 
-	if (scontext_len > len) {
+	if (scontext_len > len)
 		err = -ERANGE;
-		goto out_len;
-	}
-
-	if (copy_to_user(optval, scontext, scontext_len))
-		err = -EFAULT;
+	else
+		*optval = scontext;
 
-out_len:
-	if (put_user(scontext_len, optlen))
-		err = -EFAULT;
-	kfree(scontext);
+	*optlen = scontext_len;
 	return err;
 }
 
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 7a30b8692b1e..40c75205a914 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3919,28 +3919,29 @@  static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
  *
  * returns zero on success, an error code otherwise
  */
-static int smack_socket_getpeersec_stream(struct socket *sock,
-					  char __user *optval,
-					  int __user *optlen, unsigned len)
+static int smack_socket_getpeersec_stream(struct socket *sock, char **optval,
+					  int *optlen, unsigned len)
 {
-	struct socket_smack *ssp;
-	char *rcp = "";
-	int slen = 1;
+	struct socket_smack *ssp = smack_sock(sock->sk);
+	char *rcp;
+	int slen;
 	int rc = 0;
 
-	ssp = smack_sock(sock->sk);
-	if (ssp->smk_packet != NULL) {
-		rcp = ssp->smk_packet->smk_known;
-		slen = strlen(rcp) + 1;
+	if (ssp->smk_packet == NULL) {
+		*optlen = 0;
+		return -EINVAL;
 	}
 
+	rcp = ssp->smk_packet->smk_known;
+	slen = strlen(rcp) + 1;
 	if (slen > len)
 		rc = -ERANGE;
-	else if (copy_to_user(optval, rcp, slen) != 0)
-		rc = -EFAULT;
-
-	if (put_user(slen, optlen) != 0)
-		rc = -EFAULT;
+	else {
+		*optval = kstrdup(rcp, GFP_KERNEL);
+		if (*optval == NULL)
+			rc = -ENOMEM;
+	}
+	*optlen = slen;
 
 	return rc;
 }