Re: [PATCH] capabilities: introduce per-process capability boundingset (v10)

From: Andrew Morgan
Date: Mon Nov 26 2007 - 22:42:42 EST

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

This looks good to me.

[As you anticipated, there is a potential merge issue with Casey's
recent addition of MAC capabilities - which will make CAP_MAC_ADMIN the
highest allocated capability: ie.,

#define CAP_LAST_CAP CAP_MAC_ADMIN

].

Signed-off-by: Andrew G. Morgan <morgan@xxxxxxxxxx>

Cheers

Andrew

Serge E. Hallyn wrote:
>>From 22da6ccb1a24d1b6fa481d990a26197c6bfdfa77 Mon Sep 17 00:00:00 2001
> From: Serge E. Hallyn <serue@xxxxxxxxxx>
> Date: Mon, 19 Nov 2007 13:54:05 -0500
> Subject: [PATCH 1/1] capabilities: introduce per-process capability bounding set (v10)
>
> 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 bounding set will not affect pP and pE immediately. It will
> only affect pP' and pE' after subsequent exec()s. It also does
> not affect pI, and exec() does not constrain pI'. So to really
> start a shell with no way of regain CAP_MKNOD, you would do
>
> prctl(PR_CAPBSET_DROP, CAP_MKNOD);
> cap_t cap = cap_get_proc();
> cap_value_t caparray[1];
> caparray[0] = CAP_MKNOD;
> cap_set_flag(cap, CAP_INHERITABLE, 1, caparray, CAP_DROP);
> cap_set_proc(cap);
> cap_free(cap);
>
> The following test program will get and set the bounding
> set (but not pI). 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 <serue@xxxxxxxxxx>
> ---
> include/linux/capability.h | 11 +++++++++--
> include/linux/init_task.h | 12 ++++++++++++
> 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 | 13 ++++++++++++-
> kernel/sysctl.c | 35 -----------------------------------
> kernel/sysctl_check.c | 7 -------
> security/commoncap.c | 44 +++++++++++++++++++++++++++-----------------
> 11 files changed, 66 insertions(+), 71 deletions(-)
>
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index a1d93da..ffe7bab 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -152,7 +152,9 @@ typedef struct kernel_cap_struct {
> * Transfer any capability in your permitted set to any pid,
> * 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
> + * Add any capability from current's capability bounding set
> + * to the current process' inheritable set
> + * Allow taking bits out of capability bounding set
> */
>
> #define CAP_SETPCAP 8
> @@ -202,7 +204,6 @@ 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 +315,10 @@ typedef struct kernel_cap_struct {
>
> #define CAP_SETFCAP 31
>
> +#define CAP_LAST_CAP CAP_SETFCAP
> +
> +#define cap_valid(x) ((x) >= 0 && (x) <= CAP_LAST_CAP)
> +
> /*
> * Bit location of each capability (used by user-space library and kernel)
> */
> @@ -465,6 +470,8 @@ extern const kernel_cap_t __cap_init_eff_set;
> int capable(int cap);
> int __capable(struct task_struct *t, int cap);
>
> +extern long cap_prctl_drop(unsigned long cap);
> +
> #endif /* __KERNEL__ */
>
> #endif /* !_LINUX_CAPABILITY_H */
> diff --git a/include/linux/init_task.h b/include/linux/init_task.h
> index cae35b6..83975d9 100644
> --- a/include/linux/init_task.h
> +++ b/include/linux/init_task.h
> @@ -114,6 +114,17 @@ extern struct group_info init_groups;
> .pid = &init_struct_pid, \
> }
>
> +#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
> +/*
> + * Because of the reduced scope of CAP_SETPCAP when filesystem
> + * capabilities are in effect, it is safe to allow CAP_SETPCAP to
> + * be available in the default configuration.
> + */
> +# define CAP_INIT_BSET CAP_FULL_SET
> +#else
> +# define CAP_INIT_BSET CAP_INIT_EFF_SET
> +#endif
> +
> /*
> * INIT_TASK is used to set up the first task table, touch at
> * your own risk!. Base=0, limit=0x1fffff (=2MB)
> @@ -147,6 +158,7 @@ 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..efc495e 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1637,7 +1637,7 @@ asmlinkage long sys_umask(int mask)
> mask = xchg(&current->fs->umask, mask & S_IRWXUGO);
> return mask;
> }
> -
> +
> asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
> unsigned long arg4, unsigned long arg5)
> {
> @@ -1742,6 +1742,17 @@ 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:
> +#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
> + return cap_prctl_drop(arg2);
> +#else
> + return -EINVAL;
> +#endif
> +
> 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..cb71bb0 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -25,20 +25,6 @@
> #include <linux/mount.h>
> #include <linux/sched.h>
>
> -#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 /* ie. ndef CONFIG_SECURITY_FILE_CAPABILITIES */
> -# 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 */
> @@ -133,6 +119,12 @@ int cap_capset_check (struct task_struct *target, kernel_cap_t *effective,
> /* incapable of using this inheritable set */
> return -EPERM;
> }
> + if (!!cap_issubset(*inheritable,
> + cap_combine(target->cap_inheritable,
> + current->cap_bset))) {
> + /* no new pI capabilities outside bounding set */
> + return -EPERM;
> + }
>
> /* verify restrictions on target's new Permitted set */
> if (!cap_issubset (*permitted,
> @@ -330,10 +322,11 @@ 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);
> - working = cap_intersect (bprm->cap_inheritable,
> + 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);
> + new_permitted = cap_combine(new_permitted, working);
>
> if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
> !cap_issubset (new_permitted, current->cap_permitted)) {
> @@ -565,6 +558,23 @@ 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);
> + return 0;
> +}
> #else
> int cap_task_setscheduler (struct task_struct *p, int policy,
> struct sched_param *lp)
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.6 (GNU/Linux)

iD8DBQFHS5IeQheEq9QabfIRAu+mAJ9jZRoYVT75lv3hjtfMCArnorIQfwCdFV/J
Z0EkH2TwcGqEO9JaDrnWXNE=
=9LbV
-----END PGP SIGNATURE-----
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/