[Devel] [PATCH RFC] capabilities: introduce per-process capability bounding set

Serge E. Hallyn serue at us.ibm.com
Fri Sep 14 11:52:57 PDT 2007


>From bb9e794d1f2e50b59f853a5d7fea925641c68c08 Mon Sep 17 00:00:00 2001
From: sergeh at us.ibm.com <sergeh at us.ibm.com>
Date: Tue, 11 Sep 2007 13:51:10 -0700
Subject: [PATCH 1/1] capabilities: introduce per-process capability bounding set

The capability bounding set is a set beyond which capabilities
cannot grow.  Currently cap_bset is per-system.  It can be
manipulated through sysctl, but only init can add capabilities.
Root can remove capabilities.  By default it includes all caps
except CAP_SETPCAP.

This patch makes the bounding set per-process.  It is inherited
at fork from parent.  Noone can add elements, CAP_SYS_ADMIN is
required to remove them.  Perhaps a new capability should be
introduced to control the ability to remove capabilities, in
order to help prevent running a privileged app with enough
privs to be dangerous but not enough to be successful.

One example use of this is to start a safer container.  For
instance, until device namespaces or per-container device
whitelists are introduced, it is best to take CAP_MKNOD away
from a container.

Signed-off-by: Serge Hallyn <serue at us.ibm.com>
---
 include/linux/capability.h |   12 +++++++++++-
 include/linux/init_task.h  |    1 +
 include/linux/prctl.h      |    4 ++++
 include/linux/sched.h      |    2 +-
 include/linux/security.h   |    5 -----
 include/linux/sysctl.h     |    3 ---
 kernel/fork.c              |    1 +
 kernel/sys.c               |   10 ++++++++++
 kernel/sysctl.c            |   35 -----------------------------------
 kernel/sysctl_check.c      |    7 -------
 security/commoncap.c       |    6 ++----
 11 files changed, 30 insertions(+), 56 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index 7a8d7ad..25b83bb 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -197,7 +197,6 @@ typedef __u32 kernel_cap_t;
 #define CAP_IPC_OWNER        15
 
 /* Insert and remove kernel modules - modify kernel without limit */
-/* Modify cap_bset */
 #define CAP_SYS_MODULE       16
 
 /* Allow ioperm/iopl access */
@@ -332,6 +331,17 @@ typedef __u32 kernel_cap_t;
 #define CAP_INIT_EFF_SET    to_cap_t(~0 & ~CAP_TO_MASK(CAP_SETPCAP))
 #define CAP_INIT_INH_SET    to_cap_t(0)
 
+#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
+/*
+ * Because of the reduced scope of CAP_SETPCAP when filesystem
+ * capabilities are in effect, it is safe to allow this capability to
+ * be available in the default configuration.
+ */
+# define CAP_INIT_BSET  CAP_FULL_SET
+#else
+# define CAP_INIT_BSET  CAP_INIT_EFF_SET
+#endif
+
 #define CAP_TO_MASK(x) (1 << (x))
 #define cap_raise(c, flag)   (cap_t(c) |=  CAP_TO_MASK(flag))
 #define cap_lower(c, flag)   (cap_t(c) &= ~CAP_TO_MASK(flag))
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 1ac10c0..20e91ea 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -146,6 +146,7 @@ extern struct group_info init_groups;
 	.cap_effective	= CAP_INIT_EFF_SET,				\
 	.cap_inheritable = CAP_INIT_INH_SET,				\
 	.cap_permitted	= CAP_FULL_SET,					\
+	.cap_bset 	= CAP_INIT_BSET,				\
 	.keep_capabilities = 0,						\
 	.user		= INIT_USER,					\
 	.comm		= "swapper",					\
diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index e2eff90..a7de023 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -63,4 +63,8 @@
 #define PR_GET_SECCOMP	21
 #define PR_SET_SECCOMP	22
 
+/* Get/set the capability bounding set */
+#define PR_GET_CAPBSET 23
+#define PR_SET_CAPBSET 24
+
 #endif /* _LINUX_PRCTL_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f6cf87e..f964743 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -973,7 +973,7 @@ struct task_struct {
 	uid_t uid,euid,suid,fsuid;
 	gid_t gid,egid,sgid,fsgid;
 	struct group_info *group_info;
-	kernel_cap_t   cap_effective, cap_inheritable, cap_permitted;
+	kernel_cap_t   cap_effective, cap_inheritable, cap_permitted, cap_bset;
 	unsigned keep_capabilities:1;
 	struct user_struct *user;
 #ifdef CONFIG_KEYS
diff --git a/include/linux/security.h b/include/linux/security.h
index 13d48fd..4a62edc 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -34,11 +34,6 @@
 #include <linux/xfrm.h>
 #include <net/flow.h>
 
-/*
- * Bounding set
- */
-extern kernel_cap_t cap_bset;
-
 extern unsigned securebits;
 
 struct ctl_table;
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index e99171f..3771782 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -103,7 +103,6 @@ enum
 	KERN_NODENAME=7,
 	KERN_DOMAINNAME=8,
 
-	KERN_CAP_BSET=14,	/* int: capability bounding set */
 	KERN_PANIC=15,		/* int: panic timeout */
 	KERN_REALROOTDEV=16,	/* real root device to mount after initrd */
 
@@ -968,8 +967,6 @@ extern int proc_dostring(struct ctl_table *, int, struct file *,
 			 void __user *, size_t *, loff_t *);
 extern int proc_dointvec(struct ctl_table *, int, struct file *,
 			 void __user *, size_t *, loff_t *);
-extern int proc_dointvec_bset(struct ctl_table *, int, struct file *,
-			      void __user *, size_t *, loff_t *);
 extern int proc_dointvec_minmax(struct ctl_table *, int, struct file *,
 				void __user *, size_t *, loff_t *);
 extern int proc_dointvec_jiffies(struct ctl_table *, int, struct file *,
diff --git a/kernel/fork.c b/kernel/fork.c
index a966c53..7331d62 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1072,6 +1072,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 #ifdef CONFIG_SECURITY
 	p->security = NULL;
 #endif
+	p->cap_bset = current->cap_bset;
 	p->io_context = NULL;
 	p->audit_context = NULL;
 	container_fork(p);
diff --git a/kernel/sys.c b/kernel/sys.c
index 787b73e..53c09fb 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1740,6 +1740,16 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
 		case PR_SET_SECCOMP:
 			error = prctl_set_seccomp(arg2);
 			break;
+		case PR_GET_CAPBSET:
+			error = put_user(current->cap_bset, (unsigned long __user *)arg2);
+			break;
+		case PR_SET_CAPBSET:
+			if (!capable(CAP_SYS_ADMIN))
+				return -EPERM;
+			if (!cap_issubset(arg2, current->cap_bset))
+				return -EINVAL;
+			current->cap_bset = arg2;
+			break;
 
 		default:
 			error = -EINVAL;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index dc2378d..b46e4a9 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -377,15 +377,6 @@ static struct ctl_table kern_table[] = {
 		.proc_handler	= &proc_dointvec_taint,
 	},
 #endif
-#ifdef CONFIG_SECURITY_CAPABILITIES
-	{
-		.procname	= "cap-bound",
-		.data		= &cap_bset,
-		.maxlen		= sizeof(kernel_cap_t),
-		.mode		= 0600,
-		.proc_handler	= &proc_dointvec_bset,
-	},
-#endif /* def CONFIG_SECURITY_CAPABILITIES */
 #ifdef CONFIG_BLK_DEV_INITRD
 	{
 		.ctl_name	= KERN_REALROOTDEV,
@@ -1915,26 +1906,6 @@ static int do_proc_dointvec_bset_conv(int *negp, unsigned long *lvalp,
 	return 0;
 }
 
-#ifdef CONFIG_SECURITY_CAPABILITIES
-/*
- *	init may raise the set.
- */
-
-int proc_dointvec_bset(struct ctl_table *table, int write, struct file *filp,
-			void __user *buffer, size_t *lenp, loff_t *ppos)
-{
-	int op;
-
-	if (write && !capable(CAP_SYS_MODULE)) {
-		return -EPERM;
-	}
-
-	op = is_global_init(current) ? OP_SET : OP_AND;
-	return do_proc_dointvec(table,write,filp,buffer,lenp,ppos,
-				do_proc_dointvec_bset_conv,&op);
-}
-#endif /* def CONFIG_SECURITY_CAPABILITIES */
-
 /*
  *	Taint values can only be increased
  */
@@ -2348,12 +2319,6 @@ int proc_dointvec(struct ctl_table *table, int write, struct file *filp,
 	return -ENOSYS;
 }
 
-int proc_dointvec_bset(struct ctl_table *table, int write, struct file *filp,
-			void __user *buffer, size_t *lenp, loff_t *ppos)
-{
-	return -ENOSYS;
-}
-
 int proc_dointvec_minmax(struct ctl_table *table, int write, struct file *filp,
 		    void __user *buffer, size_t *lenp, loff_t *ppos)
 {
diff --git a/kernel/sysctl_check.c b/kernel/sysctl_check.c
index 3c9ef5a..41c7f16 100644
--- a/kernel/sysctl_check.c
+++ b/kernel/sysctl_check.c
@@ -38,10 +38,6 @@ static struct trans_ctl_table trans_kern_table[] = {
 	{ KERN_NODENAME,		"hostname" },
 	{ KERN_DOMAINNAME,		"domainname" },
 
-#ifdef CONFIG_SECURITY_CAPABILITIES
-	{ KERN_CAP_BSET,		"cap-bound" },
-#endif /* def CONFIG_SECURITY_CAPABILITIES */
-
 	{ KERN_PANIC,			"panic" },
 	{ KERN_REALROOTDEV,		"real-root-dev" },
 
@@ -1535,9 +1531,6 @@ int sysctl_check_table(struct ctl_table *table)
 			    (table->strategy == sysctl_ms_jiffies) ||
 			    (table->proc_handler == proc_dostring) ||
 			    (table->proc_handler == proc_dointvec) ||
-#ifdef CONFIG_SECURITY_CAPABILITIES
-			    (table->proc_handler == proc_dointvec_bset) ||
-#endif /* def CONFIG_SECURITY_CAPABILITIES */
 			    (table->proc_handler == proc_dointvec_minmax) ||
 			    (table->proc_handler == proc_dointvec_jiffies) ||
 			    (table->proc_handler == proc_dointvec_userhz_jiffies) ||
diff --git a/security/commoncap.c b/security/commoncap.c
index 43f9027..46e03e3 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -36,9 +36,6 @@
 # define CAP_INIT_BSET  CAP_INIT_EFF_SET
 #endif /* def CONFIG_SECURITY_FILE_CAPABILITIES */
 
-kernel_cap_t cap_bset = CAP_INIT_BSET;    /* systemwide capability bound */
-EXPORT_SYMBOL(cap_bset);
-
 /* Global security state */
 
 unsigned securebits = SECUREBITS_DEFAULT; /* systemwide security settings */
@@ -307,7 +304,8 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
 	/* Derived from fs/exec.c:compute_creds. */
 	kernel_cap_t new_permitted, working;
 
-	new_permitted = cap_intersect (bprm->cap_permitted, cap_bset);
+	new_permitted = cap_intersect (bprm->cap_permitted,
+				 current->cap_bset);
 	working = cap_intersect (bprm->cap_inheritable,
 				 current->cap_inheritable);
 	new_permitted = cap_combine (new_permitted, working);
-- 
1.5.1

_______________________________________________
Containers mailing list
Containers at lists.linux-foundation.org
https://lists.linux-foundation.org/mailman/listinfo/containers




More information about the Devel mailing list