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Date: Thu, 26 Feb 2015 15:09:48 -0600 (CST)
From: Christoph Lameter <cl@...ux.com>
To: "Serge E. Hallyn" <serge@...lyn.com>
cc: Serge Hallyn <serge.hallyn@...ntu.com>,
Serge Hallyn <serge.hallyn@...onical.com>,
Andy Lutomirski <luto@...capital.net>,
Aaron Jones <aaronmdjones@...il.com>, Ted Ts'o <tytso@....edu>,
linux-security-module@...r.kernel.org, akpm@...uxfoundation.org,
"Andrew G. Morgan" <morgan@...nel.org>,
Mimi Zohar <zohar@...ux.vnet.ibm.com>,
Austin S Hemmelgarn <ahferroin7@...il.com>,
Markku Savela <msa@...h.iki.fi>,
Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
Michael Kerrisk <mtk.manpages@...il.com>,
Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] capabilities: Ambient capability set V1
On Thu, 26 Feb 2015, Serge E. Hallyn wrote:
> > Same problem as before. The ambient bits will not be set in pE'.
>
> And what if I weren't scatterbrained and we did
>
> if (pA)
> pE' = pP'
> else
> pE' = pP' & fE
>
> All pP' bits would be set in pE'.
Ok and the non ambient case would break because fE is not available?
Doesnt this reduce to
pE' = pP'
in either case?
Here is a a patch that does just that. The patch works. Maybe I just dont
understand how this is supposed to work.
Subject: [PATCH] capabilities: Ambient capability set V2(draft)
V1->V2(draft):
- Modify bit calculations.
Signed-off-by: Christoph Lameter <cl@...ux.com>
Index: linux/security/commoncap.c
===================================================================
--- linux.orig/security/commoncap.c 2015-02-25 13:43:06.929973954 -0600
+++ linux/security/commoncap.c 2015-02-26 12:36:32.361726374 -0600
@@ -347,15 +347,16 @@ static inline int bprm_caps_from_vfs_cap
*has_cap = true;
CAP_FOR_EACH_U32(i) {
+ __u32 ambient = current_cred()->cap_ambient.cap[i];
__u32 permitted = caps->permitted.cap[i];
__u32 inheritable = caps->inheritable.cap[i];
/*
- * pP' = (X & fP) | (pI & fI)
+ * pP' = (X & fP) | (pI & (fI | pA))
*/
new->cap_permitted.cap[i] =
(new->cap_bset.cap[i] & permitted) |
- (new->cap_inheritable.cap[i] & inheritable);
+ (new->cap_inheritable.cap[i] & (inheritable | ambient));
if (permitted & ~new->cap_permitted.cap[i])
/* insufficient to execute correctly */
@@ -453,8 +454,12 @@ static int get_file_caps(struct linux_bi
if (rc == -EINVAL)
printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
__func__, rc, bprm->filename);
- else if (rc == -ENODATA)
+ else if (rc == -ENODATA) {
rc = 0;
+ /* The ambient caps are permitted for files that have no caps */
+ bprm->cred->cap_permitted = bprm->cred->cap_effective =
+ current_cred()->cap_ambient;
+ }
goto out;
}
@@ -548,10 +553,16 @@ skip:
new->suid = new->fsuid = new->euid;
new->sgid = new->fsgid = new->egid;
- if (effective)
- new->cap_effective = new->cap_permitted;
- else
- cap_clear(new->cap_effective);
+ /* pE' = pP' & (fE | pA)
+ new->cap_effective = cap_intersect(new->cap_permitted,
+ cap_combine(new->cap_effective, old->cap_ambient));
+ */
+
+ /* fE is not available */
+ new->cap_effective = new->cap_permitted;
+
+ /* pA' = pA */
+ new->cap_ambient = old->cap_ambient;
bprm->cap_effective = effective;
/*
@@ -566,7 +577,7 @@ skip:
* Number 1 above might fail if you don't have a full bset, but I think
* that is interesting information to audit.
*/
- if (!cap_isclear(new->cap_effective)) {
+ if (!cap_issubset(new->cap_effective, new->cap_ambient)) {
if (!cap_issubset(CAP_FULL_SET, new->cap_effective) ||
!uid_eq(new->euid, root_uid) || !uid_eq(new->uid, root_uid) ||
issecure(SECURE_NOROOT)) {
@@ -598,7 +609,7 @@ int cap_bprm_secureexec(struct linux_bin
if (!uid_eq(cred->uid, root_uid)) {
if (bprm->cap_effective)
return 1;
- if (!cap_isclear(cred->cap_permitted))
+ if (!cap_issubset(cred->cap_permitted, cred->cap_ambient))
return 1;
}
@@ -933,6 +944,23 @@ 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;
+
+ if (!ns_capable(current_user_ns(), arg2))
+ return -EPERM;
+
+ 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 2015-02-25 13:43:06.929973954 -0600
+++ linux/include/linux/cred.h 2015-02-25 13:43:06.925972078 -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 2015-02-25 13:43:06.929973954 -0600
+++ linux/include/uapi/linux/prctl.h 2015-02-25 13:43:06.925972078 -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 */
Index: linux/fs/proc/array.c
===================================================================
--- linux.orig/fs/proc/array.c 2015-02-25 13:43:06.929973954 -0600
+++ linux/fs/proc/array.c 2015-02-25 13:43:06.925972078 -0600
@@ -302,7 +302,8 @@ static void render_cap_t(struct seq_file
static inline void task_cap(struct seq_file *m, struct task_struct *p)
{
const struct cred *cred;
- kernel_cap_t cap_inheritable, cap_permitted, cap_effective, cap_bset;
+ kernel_cap_t cap_inheritable, cap_permitted, cap_effective,
+ cap_bset, cap_ambient;
rcu_read_lock();
cred = __task_cred(p);
@@ -310,12 +311,14 @@ static inline void task_cap(struct seq_f
cap_permitted = cred->cap_permitted;
cap_effective = cred->cap_effective;
cap_bset = cred->cap_bset;
+ cap_ambient = cred->cap_ambient;
rcu_read_unlock();
render_cap_t(m, "CapInh:\t", &cap_inheritable);
render_cap_t(m, "CapPrm:\t", &cap_permitted);
render_cap_t(m, "CapEff:\t", &cap_effective);
render_cap_t(m, "CapBnd:\t", &cap_bset);
+ render_cap_t(m, "CapAmb:\t", &cap_ambient);
}
static inline void task_seccomp(struct seq_file *m, struct task_struct *p)
--
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