An attempt to implement this. Probably missing some fine points:
Subject: [capabilities] Implement ambient capability set.
DRAFT -- untested -- DRAFT
Implement an ambient capabilty set to allow capabilties
to be inherited with unix semantics used also for other
attributes.
Implements PR_CAP_AMBIENT. The second argument to prctl
is a the capability number and the third the desired state.
0 for off. Otherwise on.
Serge:
A new capability set, pA, is empty by default. You can
add bits to it using prctl if ns_capable(CAP_SETPCAP) and
all the new bits are in your pE. Once set, they stay until
they are removed using prctl. At exec, pA' = pA, and
fI |= pA (after reading fI from disk but before
calculating pI').
Since the ambient caps "stay on" cap_inheritable does not
really matter anymore. Simply set the permitted caps when
the ambient cap is set.
Signed-off-by: Christoph Lameter <c...@linux.com>
Index: linux/security/commoncap.c
===================================================================
--- linux.orig/security/commoncap.c 2015-02-04 09:44:25.000000000 -0600
+++ linux/security/commoncap.c 2015-02-04 12:48:44.100471600 -0600
@@ -353,7 +353,7 @@ static inline int bprm_caps_from_vfs_cap
/*
* pP' = (X & fP) | (pI & fI)
*/
- new->cap_permitted.cap[i] =
+ new->cap_permitted.cap[i] = current_cred()->cap_ambient.cap[i] |
(new->cap_bset.cap[i] & permitted) |
(new->cap_inheritable.cap[i] & inheritable);
@@ -577,6 +577,7 @@ skip:
}
new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
+ new->cap_ambient = old->cap_ambient;
return 0;
}
@@ -933,6 +934,20 @@ int cap_task_prctl(int option, unsigned
new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
return commit_creds(new);
+ case PR_CAP_AMBIENT:
+ if (!ns_capable(current_user_ns(), CAP_SETPCAP))
+ return -EPERM;
+
+ if (!cap_valid(arg2))
+ return -EINVAL;
+
+ new =prepare_creds();
+ if (arg3 == 0)
+ cap_lower(new->cap_ambient, arg2);
+ else
+ cap_raise(new->cap_ambient, arg2);
+ return commit_creds(new);
+
default:
/* No functionality available - continue with default */
return -ENOSYS;
Index: linux/include/linux/cred.h
===================================================================
--- linux.orig/include/linux/cred.h 2015-02-04 09:39:46.000000000 -0600
+++ linux/include/linux/cred.h 2015-02-04 12:32:43.719846530 -0600
@@ -122,6 +122,7 @@ struct cred {
kernel_cap_t cap_permitted; /* caps we're permitted */
kernel_cap_t cap_effective; /* caps we can actually use */
kernel_cap_t cap_bset; /* capability bounding set */
+ kernel_cap_t cap_ambient; /* Ambient capability set */
#ifdef CONFIG_KEYS
unsigned char jit_keyring; /* default keyring to attach requested
* keys to */
Index: linux/include/uapi/linux/prctl.h
===================================================================
--- linux.orig/include/uapi/linux/prctl.h 2014-12-12 10:27:49.332800377
-0600
+++ linux/include/uapi/linux/prctl.h 2015-02-04 12:39:10.651205059 -0600
@@ -185,4 +185,7 @@ struct prctl_mm_map {
#define PR_MPX_ENABLE_MANAGEMENT 43
#define PR_MPX_DISABLE_MANAGEMENT 44
+/* Control the ambient capability set */
+#define PR_CAP_AMBIENT 45
+
#endif /* _LINUX_PRCTL_H */
--
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