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From: Jann Horn <jannh@google.com>
To: Paul Moore <paul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>,
	selinux@tycho.nsa.gov, jannh@google.com
Cc: James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH] selinux: stricter parsing in mls_context_to_sid()
Date: Fri,  3 Aug 2018 11:36:04 +0200	[thread overview]
Message-ID: <20180803093604.38254-1-jannh@google.com> (raw)

mls_context_to_sid incorrectly accepted MLS context strings that are
followed by a dash and trailing garbage.

Before this change, the following command works:

# mount -t tmpfs -o 'context=system_u:object_r:tmp_t:s0-s0:c0-BLAH' \
none mount

After this change, it fails with the following error message in dmesg:

SELinux: security_context_str_to_sid(system_u:object_r:tmp_t:s0-s0:c0-BLAH)
failed for (dev tmpfs, type tmpfs) errno=-22

This is not an important bug; but it is a small quirk that was useful for
exploiting a vulnerability in fusermount.

This patch does not change the behavior when the policy does not have MLS
enabled.

Signed-off-by: Jann Horn <jannh@google.com>
---
 security/selinux/ss/mls.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
index 39475fb455bc..2c73d612d2ee 100644
--- a/security/selinux/ss/mls.c
+++ b/security/selinux/ss/mls.c
@@ -344,7 +344,7 @@ int mls_context_to_sid(struct policydb *pol,
 					break;
 			}
 		}
-		if (delim == '-') {
+		if (delim == '-' && l == 0) {
 			/* Extract high sensitivity. */
 			scontextp = p;
 			while (*p && *p != ':')
-- 
2.18.0.597.ga71716f1ad-goog


WARNING: multiple messages have this Message-ID (diff)
From: jannh@google.com (Jann Horn)
To: linux-security-module@vger.kernel.org
Subject: [PATCH] selinux: stricter parsing in mls_context_to_sid()
Date: Fri,  3 Aug 2018 11:36:04 +0200	[thread overview]
Message-ID: <20180803093604.38254-1-jannh@google.com> (raw)

mls_context_to_sid incorrectly accepted MLS context strings that are
followed by a dash and trailing garbage.

Before this change, the following command works:

# mount -t tmpfs -o 'context=system_u:object_r:tmp_t:s0-s0:c0-BLAH' \
none mount

After this change, it fails with the following error message in dmesg:

SELinux: security_context_str_to_sid(system_u:object_r:tmp_t:s0-s0:c0-BLAH)
failed for (dev tmpfs, type tmpfs) errno=-22

This is not an important bug; but it is a small quirk that was useful for
exploiting a vulnerability in fusermount.

This patch does not change the behavior when the policy does not have MLS
enabled.

Signed-off-by: Jann Horn <jannh@google.com>
---
 security/selinux/ss/mls.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/selinux/ss/mls.c b/security/selinux/ss/mls.c
index 39475fb455bc..2c73d612d2ee 100644
--- a/security/selinux/ss/mls.c
+++ b/security/selinux/ss/mls.c
@@ -344,7 +344,7 @@ int mls_context_to_sid(struct policydb *pol,
 					break;
 			}
 		}
-		if (delim == '-') {
+		if (delim == '-' && l == 0) {
 			/* Extract high sensitivity. */
 			scontextp = p;
 			while (*p && *p != ':')
-- 
2.18.0.597.ga71716f1ad-goog

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             reply	other threads:[~2018-08-03  9:36 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-03  9:36 Jann Horn [this message]
2018-08-03  9:36 ` [PATCH] selinux: stricter parsing in mls_context_to_sid() Jann Horn
2018-08-04  0:01 ` Paul Moore
2018-08-04  0:01   ` Paul Moore
2018-08-06 19:47   ` Jann Horn
2018-08-06 19:47     ` Jann Horn
2018-08-06 12:58 ` Stephen Smalley
2018-08-06 12:58   ` Stephen Smalley

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