linux-kernel - [PATCH V2] security/selinux: Always allow FIOCLEX and FIONCLEX

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Date:   Mon, 21 Feb 2022 13:15:33 +0000
From:   Richard Haines <richard_c_haines@...nternet.com>
To:     paul@...l-moore.com, stephen.smalley.work@...il.com,
        eparis@...isplace.org, demiobenour@...il.com
Cc:     selinux@...r.kernel.org, linux-kernel@...r.kernel.org,
        selinux-refpolicy@...r.kernel.org, jeffv@...gle.com,
        Richard Haines <richard_c_haines@...nternet.com>
Subject: [PATCH V2] security/selinux: Always allow FIOCLEX and FIONCLEX

These ioctls are equivalent to fcntl(fd, F_SETFD, flags), which SELinux
always allows too.  Furthermore, a failed FIOCLEX could result in a file
descriptor being leaked to a process that should not have access to it.

As this patch removes access controls, a policy capability needs to be
enabled in policy to always allow these ioctls.

Based-on-patch-by: Demi Marie Obenour <demiobenour@...il.com>
Signed-off-by: Richard Haines <richard_c_haines@...nternet.com>
---
V2 Change: Control via a policy capability. See this thread for discussion:
https://lore.kernel.org/selinux/CAHC9VhQEPxYP_KU56gAGNHKQaxucY8gSsHiUB42PVgADBAccRQ@mail.gmail.com/T/#t

With this patch and the polcap enabled, the selinux-testsuite will fail:
ioctl/test at line 47 - Will need a fix.

 security/selinux/hooks.c                   | 7 +++++++
 security/selinux/include/policycap.h       | 1 +
 security/selinux/include/policycap_names.h | 3 ++-
 security/selinux/include/security.h        | 7 +++++++
 4 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 5b6895e4f..030c41652 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3745,6 +3745,13 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
 					    CAP_OPT_NONE, true);
 		break;
 
+	case FIOCLEX:
+	case FIONCLEX:
+		/* Must always succeed if polcap set, else default: */
+		if (selinux_policycap_ioctl_skip_cloexec())
+			break;
+		fallthrough;
+
 	/* default case assumes that the command will go
 	 * to the file's ioctl() function.
 	 */
diff --git a/security/selinux/include/policycap.h b/security/selinux/include/policycap.h
index 2ec038efb..44d73dc32 100644
--- a/security/selinux/include/policycap.h
+++ b/security/selinux/include/policycap.h
@@ -11,6 +11,7 @@ enum {
 	POLICYDB_CAPABILITY_CGROUPSECLABEL,
 	POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION,
 	POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS,
+	POLICYDB_CAPABILITY_IOCTL_CLOEXEC,
 	__POLICYDB_CAPABILITY_MAX
 };
 #define POLICYDB_CAPABILITY_MAX (__POLICYDB_CAPABILITY_MAX - 1)
diff --git a/security/selinux/include/policycap_names.h b/security/selinux/include/policycap_names.h
index b89289f09..ebd64afe1 100644
--- a/security/selinux/include/policycap_names.h
+++ b/security/selinux/include/policycap_names.h
@@ -12,7 +12,8 @@ const char *selinux_policycap_names[__POLICYDB_CAPABILITY_MAX] = {
 	"always_check_network",
 	"cgroup_seclabel",
 	"nnp_nosuid_transition",
-	"genfs_seclabel_symlinks"
+	"genfs_seclabel_symlinks",
+	"ioctl_skip_cloexec"
 };
 
 #endif /* _SELINUX_POLICYCAP_NAMES_H_ */
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index ac0ece013..8a789c22b 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -219,6 +219,13 @@ static inline bool selinux_policycap_genfs_seclabel_symlinks(void)
 	return READ_ONCE(state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS]);
 }
 
+static inline bool selinux_policycap_ioctl_skip_cloexec(void)
+{
+	struct selinux_state *state = &selinux_state;
+
+	return READ_ONCE(state->policycap[POLICYDB_CAPABILITY_IOCTL_CLOEXEC]);
+}
+
 struct selinux_policy_convert_data;
 
 struct selinux_load_state {
-- 
2.35.1