[Devel] Re: [PATCH 5/9] cr: capabilities: define checkpoint and restore fns
Serge E. Hallyn
serue at us.ibm.com
Mon Jun 1 08:49:01 PDT 2009
Quoting Andrew G. Morgan (morgan at kernel.org):
> Serge,
>
> I'm not sure I'm too happy with hard coding the 64-bitness of
> capability sets. It may well be a very long time before we increase
> their size, but couldn't you prepare for that with some reference to
> the prevailing magic numbers for the current ABI representation?
Is the appended, updated version of the patch ok?
> Also, the use of 'error' as both a variable and a goto destination
> looks a little confusing.
Ok, but that was in the original code. I can send a separate
patch for mainline to change that, but it's not hurting
anything at the moment so not sure it's worth it?
-serge
>From aa72f022fb5788ab46658e6eb94eaf18e8c6568a Mon Sep 17 00:00:00 2001
From: Serge E. Hallyn <serue at us.ibm.com>
Date: Mon, 11 May 2009 09:44:42 -0400
Subject: [PATCH 5/9] cr: capabilities: define checkpoint and restore fns
An application checkpoint image will store capability sets
(and the bounding set) as __u64s. Define checkpoint and
restart functions to translate between those and kernel_cap_t's.
Define a common function do_capset_tocred() which applies capability
set changes to a passed-in struct cred.
The restore function uses do_capset_tocred() to apply the restored
capabilities to the struct cred being crafted, subject to the
current task's (task executing sys_restart()) permissions.
Changelog:
Jun 01: Add commented BUILD_BUG_ON() to point out that the
current implementation depends on 64-bit capabilities.
(Andrew Morgan and Alexey Dobriyan).
May 28: add helpers to c/r securebits
Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
---
include/linux/capability.h | 7 +++
kernel/capability.c | 102 ++++++++++++++++++++++++++++++++++++++------
security/commoncap.c | 51 +++++++++++++++-------
3 files changed, 130 insertions(+), 30 deletions(-)
diff --git a/include/linux/capability.h b/include/linux/capability.h
index c302110..b3853ca 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -536,6 +536,13 @@ extern const kernel_cap_t __cap_empty_set;
extern const kernel_cap_t __cap_full_set;
extern const kernel_cap_t __cap_init_eff_set;
+extern void checkpoint_save_cap(__u64 *dest, kernel_cap_t src);
+struct cred;
+extern int checkpoint_restore_cap(__u64 e, __u64 i, __u64 p, __u64 x,
+ struct cred *cred);
+extern void checkpoint_save_securebits(unsigned *, unsigned);
+extern int checkpoint_restore_securebits(unsigned, struct cred *);
+
/**
* has_capability - Determine if a task has a superior capability available
* @t: The task in question
diff --git a/kernel/capability.c b/kernel/capability.c
index 4e17041..6bfd180 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -217,6 +217,45 @@ SYSCALL_DEFINE2(capget, cap_user_header_t, header, cap_user_data_t, dataptr)
return ret;
}
+static int do_capset_tocred(kernel_cap_t *effective, kernel_cap_t *inheritable,
+ kernel_cap_t *permitted, struct cred *new)
+{
+ int ret;
+
+ ret = security_capset(new, current_cred(),
+ effective, inheritable, permitted);
+ if (ret < 0)
+ return ret;
+
+ /*
+ * for checkpoint-restart, do we want to wait until end of restart?
+ * not sure we care */
+ audit_log_capset(current->pid, new, current_cred());
+
+ return 0;
+}
+
+static int do_capset(kernel_cap_t *effective, kernel_cap_t *inheritable,
+ kernel_cap_t *permitted)
+{
+ struct cred *new;
+ int ret;
+
+ new = prepare_creds();
+ if (!new)
+ return -ENOMEM;
+
+ ret = do_capset_tocred(effective, inheritable, permitted, new);
+ if (ret < 0)
+ goto error;
+
+ return commit_creds(new);
+
+error:
+ abort_creds(new);
+ return ret;
+}
+
/**
* sys_capset - set capabilities for a process or (*) a group of processes
* @header: pointer to struct that contains capability version and
@@ -240,7 +279,6 @@ SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
unsigned i, tocopy;
kernel_cap_t inheritable, permitted, effective;
- struct cred *new;
int ret;
pid_t pid;
@@ -271,22 +309,60 @@ SYSCALL_DEFINE2(capset, cap_user_header_t, header, const cap_user_data_t, data)
i++;
}
- new = prepare_creds();
- if (!new)
- return -ENOMEM;
+ return do_capset(&effective, &inheritable, &permitted);
- ret = security_capset(new, current_cred(),
- &effective, &inheritable, &permitted);
- if (ret < 0)
- goto error;
+}
- audit_log_capset(pid, new, current_cred());
+void checkpoint_save_cap(__u64 *dest, kernel_cap_t src)
+{
- return commit_creds(new);
+ /*
+ * If the following triggers, then capabilities no longer fit into
+ * 64 bits. The checkpoint image defined in include/linux/checkpoint_hdr.h
+ * as well as the checkpoint_save_cap() and checkpoint_restore_cap()
+ * helpers below need to be updated
+ */
+ BUILD_BUG_ON(CAP_LAST_CAP >= 64);
-error:
- abort_creds(new);
- return ret;
+ *dest = src.cap[0] | (src.cap[1] << sizeof(__u32));
+}
+
+static void do_capbset_drop(struct cred *cred, int cap)
+{
+ cap_lower(cred->cap_bset, cap);
+}
+
+int checkpoint_restore_cap(__u64 newe, __u64 newi, __u64 newp, __u64 newx,
+ struct cred *cred)
+{
+ kernel_cap_t effective, inheritable, permitted, bset;
+ int may_dropbcap = capable(CAP_SETPCAP);
+ int ret, i;
+
+ effective.cap[0] = newe;
+ effective.cap[1] = (newe >> sizeof(__u32));
+ inheritable.cap[0] = newi;
+ inheritable.cap[1] = (newi >> sizeof(__u32));
+ permitted.cap[0] = newp;
+ permitted.cap[1] = (newp >> sizeof(__u32));
+ bset.cap[0] = newx;
+ bset.cap[1] = (newx >> sizeof(__u32));
+
+ ret = do_capset_tocred(&effective, &inheritable, &permitted, cred);
+ if (ret < 0)
+ return ret;
+
+ for (i = 0; i < CAP_LAST_CAP; i++) {
+ if (cap_raised(bset, i))
+ continue;
+ if (!cap_raised(current_cred()->cap_bset, i))
+ continue;
+ if (!may_dropbcap)
+ return -EPERM;
+ do_capbset_drop(cred, i);
+ }
+
+ return 0;
}
/**
diff --git a/security/commoncap.c b/security/commoncap.c
index beac025..8054a07 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -804,6 +804,28 @@ int cap_task_setnice (struct task_struct *p, int nice)
}
#endif
+int cap_set_securebits(struct cred *new, unsigned securebits)
+{
+ if ((((new->securebits & SECURE_ALL_LOCKS) >> 1)
+ & (new->securebits ^ securebits)) /*[1]*/
+ || ((new->securebits & SECURE_ALL_LOCKS & ~securebits)) /*[2]*/
+ || (securebits & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
+ || (cap_capable(current, current_cred(), CAP_SETPCAP,
+ SECURITY_CAP_AUDIT) != 0) /*[4]*/
+ /*
+ * [1] no changing of bits that are locked
+ * [2] no unlocking of locks
+ * [3] no setting of unsupported bits
+ * [4] doing anything requires privilege (go read about
+ * the "sendmail capabilities bug")
+ */
+ )
+ /* cannot change a locked bit */
+ return -EPERM;
+ new->securebits = securebits;
+ return 0;
+}
+
/**
* cap_task_prctl - Implement process control functions for this security module
* @option: The process control function requested
@@ -861,24 +883,9 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
* capability-based-privilege environment.
*/
case PR_SET_SECUREBITS:
- error = -EPERM;
- if ((((new->securebits & SECURE_ALL_LOCKS) >> 1)
- & (new->securebits ^ arg2)) /*[1]*/
- || ((new->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
- || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
- || (cap_capable(current, current_cred(), CAP_SETPCAP,
- SECURITY_CAP_AUDIT) != 0) /*[4]*/
- /*
- * [1] no changing of bits that are locked
- * [2] no unlocking of locks
- * [3] no setting of unsupported bits
- * [4] doing anything requires privilege (go read about
- * the "sendmail capabilities bug")
- */
- )
- /* cannot change a locked bit */
+ error = cap_set_securebits(new, arg2);
+ if (error)
goto error;
- new->securebits = arg2;
goto changed;
case PR_GET_SECUREBITS:
@@ -921,6 +928,16 @@ error:
return error;
}
+void checkpoint_save_securebits(unsigned *b, unsigned cred_securebits)
+{
+ *b = cred_securebits;
+}
+
+int checkpoint_restore_securebits(unsigned b, struct cred *cred)
+{
+ return cap_set_securebits(cred, b);
+}
+
/**
* cap_syslog - Determine whether syslog function is permitted
* @type: Function requested
--
1.6.1
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