Andrew, this version follows all of your suggestions. Definately nicer
userspace interface. thanks
-serge
>From b7c210160e3c210d63eca532289ca1c9caf1bd87 Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <[EMAIL PROTECTED]>
Date: Mon, 19 Nov 2007 13:54:05 -0500
Subject: [PATCH 1/1] capabilities: introduce per-process capability bounding
set (v8)
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 when file
capabilities are enabled. It is inherited at fork from parent.
Noone can add elements, CAP_SETPCAP is required to remove them.
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.
The following test program will get and set the bounding
set. For instance
./bset get
(lists capabilities in bset)
./bset drop cap_net_raw
(starts shell with new bset)
(use capset, setuid binary, or binary with
file capabilities to try to increase caps)
************************************************************
cap_bound.c
************************************************************
#include <sys/prctl.h>
#include <linux/capability.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifndef PR_CAPBSET_READ
#define PR_CAPBSET_READ 23
#endif
#ifndef PR_CAPBSET_DROP
#define PR_CAPBSET_DROP 24
#endif
int usage(char *me)
{
printf("Usage: %s get\n", me);
printf(" %s drop <capability>\n", me);
return 1;
}
#define numcaps 32
char *captable[numcaps] = {
"cap_chown",
"cap_dac_override",
"cap_dac_read_search",
"cap_fowner",
"cap_fsetid",
"cap_kill",
"cap_setgid",
"cap_setuid",
"cap_setpcap",
"cap_linux_immutable",
"cap_net_bind_service",
"cap_net_broadcast",
"cap_net_admin",
"cap_net_raw",
"cap_ipc_lock",
"cap_ipc_owner",
"cap_sys_module",
"cap_sys_rawio",
"cap_sys_chroot",
"cap_sys_ptrace",
"cap_sys_pacct",
"cap_sys_admin",
"cap_sys_boot",
"cap_sys_nice",
"cap_sys_resource",
"cap_sys_time",
"cap_sys_tty_config",
"cap_mknod",
"cap_lease",
"cap_audit_write",
"cap_audit_control",
"cap_setfcap"
};
int getbcap(void)
{
int comma=0;
unsigned long i;
int ret;
printf("i know of %d capabilities\n", numcaps);
printf("capability bounding set:");
for (i=0; i<numcaps; i++) {
ret = prctl(PR_CAPBSET_READ, i);
if (ret < 0)
perror("prctl");
else if (ret==1)
printf("%s%s", (comma++) ? ", " : " ", captable[i]);
}
printf("\n");
return 0;
}
int capdrop(char *str)
{
unsigned long i;
int found=0;
for (i=0; i<numcaps; i++) {
if (strcmp(captable[i], str) == 0) {
found=1;
break;
}
}
if (!found)
return 1;
if (prctl(PR_CAPBSET_DROP, i)) {
perror("prctl");
return 1;
}
return 0;
}
int main(int argc, char *argv[])
{
if (argc<2)
return usage(argv[0]);
if (strcmp(argv[1], "get")==0)
return getbcap();
if (strcmp(argv[1], "drop")!=0 || argc<3)
return usage(argv[0]);
if (capdrop(argv[2])) {
printf("unknown capability\n");
return 1;
}
return execl("/bin/bash", "/bin/bash", NULL);
}
************************************************************
Signed-off-by: Serge E. Hallyn <[EMAIL PROTECTED]>
---
include/linux/capability.h | 25 ++++++++++++++++++++++++-
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 | 7 +++++++
kernel/sysctl.c | 35 -----------------------------------
kernel/sysctl_check.c | 7 -------
security/commoncap.c | 29 +++++++++++++++++++++++++----
11 files changed, 63 insertions(+), 56 deletions(-)
diff --git a/include/linux/capability.h b/include/linux/capability.h
index a1d93da..94638b2 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -153,6 +153,7 @@ typedef struct kernel_cap_struct {
* remove any capability in your permitted set from any pid
* With VFS support for capabilities (neither of above, but)
* Add any capability to the current process' inheritable set
+ * Allow taking bits out of capability bounding set
*/
#define CAP_SETPCAP 8
@@ -202,7 +203,6 @@ typedef struct kernel_cap_struct {
#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 */
@@ -314,6 +314,10 @@ typedef struct kernel_cap_struct {
#define CAP_SETFCAP 31
+#define CAP_NUM_CAPS 32
+
+#define cap_valid(x) ((x) >= 0 && (x) < CAP_NUM_CAPS)
+
/*
* Bit location of each capability (used by user-space library and kernel)
*/
@@ -350,6 +354,17 @@ typedef struct kernel_cap_struct {
#define CAP_INIT_INH_SET CAP_EMPTY_SET
+#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_clear(c) do { (c) = __cap_empty_set; } while (0)
# define cap_set_full(c) do { (c) = __cap_full_set; } while (0)
# define cap_set_init_eff(c) do { (c) = __cap_init_eff_set; } while (0)
@@ -465,6 +480,14 @@ extern const kernel_cap_t __cap_init_eff_set;
int capable(int cap);
int __capable(struct task_struct *t, int cap);
+#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
+extern long cap_prctl_drop(unsigned long cap);
+#else
+#include <linux/errno.h>
+static inline long cap_prctl_drop(unsigned long cap)
+{ return -EINVAL; }
+#endif
+
#endif /* __KERNEL__ */
#endif /* !_LINUX_CAPABILITY_H */
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index cae35b6..5c84d14 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -147,6 +147,7 @@ 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..3800639 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_CAPBSET_READ 23
+#define PR_CAPBSET_DROP 24
+
#endif /* _LINUX_PRCTL_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 1d17f7c..bf51a16 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1041,7 +1041,7 @@ 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 f771ad8..04b18f1 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 4f5047d..fa900cb 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -102,7 +102,6 @@ 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 */
@@ -962,8 +961,6 @@ 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 5639b3e..9e4a5e1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1087,6 +1087,7 @@ 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;
cgroup_fork(p);
diff --git a/kernel/sys.c b/kernel/sys.c
index 4c77ed2..bed55dc 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1742,6 +1742,13 @@ asmlinkage long sys_prctl(int option, unsigned long
arg2, unsigned long arg3,
error = prctl_set_seccomp(arg2);
break;
+ case PR_CAPBSET_READ:
+ if (!cap_valid(arg2))
+ return -EINVAL;
+ return !!cap_raised(current->cap_bset, arg2);
+ case PR_CAPBSET_DROP:
+ return cap_prctl_drop(arg2);
+
default:
error = -EINVAL;
break;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 489b0d1..d858819 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -383,15 +383,6 @@ 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,
@@ -1910,26 +1901,6 @@ 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
*/
@@ -2343,12 +2314,6 @@ 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 8f5baac..526fa36 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" },
@@ -1522,9 +1518,6 @@ 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 3a95990..b6745f4 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 */
@@ -330,7 +327,8 @@ 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);
@@ -565,6 +563,29 @@ int cap_task_kill(struct task_struct *p, struct siginfo
*info,
return -EPERM;
}
+
+/*
+ * called from kernel/sys.c for prctl(PR_CABSET_DROP)
+ * done without task_capability_lock() because it introduces
+ * no new races - i.e. only another task doing capget() on
+ * this task could get inconsistent info. There can be no
+ * racing writer bc a task can only change its own caps.
+ */
+long cap_prctl_drop(unsigned long cap)
+{
+ if (!capable(CAP_SETPCAP))
+ return -EPERM;
+ if (!cap_valid(cap))
+ return -EINVAL;
+ cap_lower(current->cap_bset, cap);
+ current->cap_effective = cap_intersect(current->cap_effective,
+ current->cap_bset);
+ current->cap_permitted = cap_intersect(current->cap_permitted,
+ current->cap_bset);
+ current->cap_inheritable = cap_intersect(current->cap_inheritable,
+ current->cap_bset);
+ return 0;
+}
#else
int cap_task_setscheduler (struct task_struct *p, int policy,
struct sched_param *lp)
--
1.5.1.1.GIT
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