[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
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