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authorSerge E. Hallyn <serue@us.ibm.com>2008-02-05 01:29:45 -0500
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-05 12:44:20 -0500
commit3b7391de67da515c91f48aa371de77cb6cc5c07e (patch)
tree22b9f5d9d1c36b374eb5765219aca3c7e1f23486 /kernel/sys.c
parent46c383cc4530ccc438cb325e92e11eb21dd3d4fc (diff)
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 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); } ************************************************************ [serue@us.ibm.com: fix typo] Signed-off-by: Serge E. Hallyn <serue@us.ibm.com> Signed-off-by: Andrew G. Morgan <morgan@kernel.org> Cc: Stephen Smalley <sds@tycho.nsa.gov> Cc: James Morris <jmorris@namei.org> Cc: Chris Wright <chrisw@sous-sol.org> Cc: Casey Schaufler <casey@schaufler-ca.com>a Signed-off-by: "Serge E. Hallyn" <serue@us.ibm.com> Tested-by: Jiri Slaby <jirislaby@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/sys.c')
-rw-r--r--kernel/sys.c13
1 files changed, 12 insertions, 1 deletions
diff --git a/kernel/sys.c b/kernel/sys.c
index d1fe71eb4546..4162d12390b6 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1637,7 +1637,7 @@ asmlinkage long sys_umask(int mask)
1637 mask = xchg(&current->fs->umask, mask & S_IRWXUGO); 1637 mask = xchg(&current->fs->umask, mask & S_IRWXUGO);
1638 return mask; 1638 return mask;
1639} 1639}
1640 1640
1641asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3, 1641asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
1642 unsigned long arg4, unsigned long arg5) 1642 unsigned long arg4, unsigned long arg5)
1643{ 1643{
@@ -1742,6 +1742,17 @@ asmlinkage long sys_prctl(int option, unsigned long arg2, unsigned long arg3,
1742 error = prctl_set_seccomp(arg2); 1742 error = prctl_set_seccomp(arg2);
1743 break; 1743 break;
1744 1744
1745 case PR_CAPBSET_READ:
1746 if (!cap_valid(arg2))
1747 return -EINVAL;
1748 return !!cap_raised(current->cap_bset, arg2);
1749 case PR_CAPBSET_DROP:
1750#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
1751 return cap_prctl_drop(arg2);
1752#else
1753 return -EINVAL;
1754#endif
1755
1745 default: 1756 default:
1746 error = -EINVAL; 1757 error = -EINVAL;
1747 break; 1758 break;