[PATCH v18 59/80] c/r: capabilities: define checkpoint and restore fns

Oren Laadan
2009-09-24T00:30:07Z

From: Serge E. Hallyn <serue@us.ibm.com>

[ Andrew: I am punting on dealing with the subsystem cooperation
issues in this version, in favor of trying to get LSM issues
straightened out ]

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 09: Can't choose securebits or drop bounding set if
file capabilities aren't compiled into the kernel.
Also just store caps in __u32s (looks cleaner).
Jun 01: Made the checkpoint and restore functions and the
ckpt_hdr_capabilities struct more opaque to the
rest of the c/r code, as suggested by Andrew Morgan,
and using naming suggested by Oren.
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@us.ibm.com>
---
include/linux/capability.h | 6 ++
include/linux/checkpoint_hdr.h | 11 +++
kernel/capability.c | 164 +++++++++++++++++++++++++++++++++++++---
security/commoncap.c | 19 +----
4 files changed, 172 insertions(+), 28 deletions(-)

diff --git a/include/linux/capability.h b/include/linux/capability.h
index c302110..3a74655 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -568,6 +568,12 @@ extern int capable(int cap);
struct dentry;
extern int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data *cpu_caps);

+struct cred;
+int apply_securebits(unsigned securebits, struct cred *new);
+struct ckpt_capabilities;
+int restore_capabilities(struct ckpt_capabilities *h, struct cred *new);
+void checkpoint_capabilities(struct ckpt_capabilities *h, struct cred * cred);
+
#endif /* __KERNEL__ */

#endif /* !_LINUX_CAPABILITY_H */
diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h
index ef260a0..cb036e8 100644
--- a/include/linux/checkpoint_hdr.h
+++ b/include/linux/checkpoint_hdr.h
@@ -61,6 +61,7 @@ enum {
CKPT_HDR_NS,
CKPT_HDR_UTS_NS,
CKPT_HDR_IPC_NS,
+ CKPT_HDR_CAPABILITIES,

/* 201-299: reserved for arch-dependent */

@@ -192,6 +193,16 @@ struct ckpt_hdr_task {
__u64 robust_futex_list; /* a __user ptr */
} __attribute__((aligned(8)));

+/* Posix capabilities */
+struct ckpt_capabilities {
+ __u32 cap_i_0, cap_i_1; /* inheritable set */
+ __u32 cap_p_0, cap_p_1; /* permitted set */
+ __u32 cap_e_0, cap_e_1; /* effective set */
+ __u32 cap_b_0, cap_b_1; /* bounding set */
+ __u32 securebits;
+ __u32 padding;
+} __attribute__((aligned(8)));
+
/* namespaces */
struct ckpt_hdr_task_ns {
struct ckpt_hdr h;
diff --git a/kernel/capability.c b/kernel/capability.c
index 4e17041..4f58454 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -14,6 +14,8 @@
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/pid_namespace.h>
+#include <linux/securebits.h>
+#include <linux/checkpoint.h>
#include <asm/uaccess.h>
#include "cred-internals.h"

@@ -217,6 +219,45 @@ 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 +281,6 @@ 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;

@@ -271,23 +311,125 @@ 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);
+}
+
+#ifdef CONFIG_SECURITY_FILE_CAPABILITIES
+int apply_securebits(unsigned securebits, struct cred *new)
+{
+ 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;
+}
+
+static void do_capbset_drop(struct cred *cred, int cap)
+{
+ cap_lower(cred->cap_bset, cap);
+}
+
+static inline int restore_cap_bset(kernel_cap_t bset, struct cred *cred)
+{
+ int i, may_dropbcap = capable(CAP_SETPCAP);
+
+ 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;
+}
+
+#else /* CONFIG_SECURITY_FILE_CAPABILITIES */
+
+int apply_securebits(unsigned securebits, struct cred *new)
+{
+ /* settable securebits not supported */
+ return 0;
+}
+
+static inline int restore_cap_bset(kernel_cap_t bset, struct cred *cred)
+{
+ /* bounding sets not supported */
+ return 0;
+}
+#endif /* CONFIG_SECURITY_FILE_CAPABILITIES */
+
+#ifdef CONFIG_CHECKPOINT
+static int do_restore_caps(struct ckpt_capabilities *h, struct cred *cred)
+{
+ kernel_cap_t effective, inheritable, permitted, bset;
+ int ret;
+
+ effective.cap[0] = h->cap_e_0;
+ effective.cap[1] = h->cap_e_1;
+ inheritable.cap[0] = h->cap_i_0;
+ inheritable.cap[1] = h->cap_i_1;
+ permitted.cap[0] = h->cap_p_0;
+ permitted.cap[1] = h->cap_p_1;
+ bset.cap[0] = h->cap_b_0;
+ bset.cap[1] = h->cap_b_1;
+
+ ret = do_capset_tocred(&effective, &inheritable, &permitted, cred);
if (ret < 0)
- goto error;
+ return ret;
+
+ ret = restore_cap_bset(bset, cred);
+ return ret;
+}

- audit_log_capset(pid, new, current_cred());
+void checkpoint_capabilities(struct ckpt_capabilities *h, struct cred * cred)
+{
+ BUILD_BUG_ON(CAP_LAST_CAP >= 64);
+ h->securebits = cred->securebits;
+ h->cap_i_0 = cred->cap_inheritable.cap[0];
+ h->cap_i_1 = cred->cap_inheritable.cap[1];
+ h->cap_p_0 = cred->cap_permitted.cap[0];
+ h->cap_p_1 = cred->cap_permitted.cap[1];
+ h->cap_e_0 = cred->cap_effective.cap[0];
+ h->cap_e_1 = cred->cap_effective.cap[1];
+ h->cap_b_0 = cred->cap_bset.cap[0];
+ h->cap_b_1 = cred->cap_bset.cap[1];
+}

- return commit_creds(new);
+/*
+ * restore_capabilities: called by restore_creds() to set the
+ * restored capabilities (if permitted) in a new struct cred which
+ * will be attached at the end of the sys_restart().
+ * struct cred *new is prepared by caller (using prepare_creds())
+ * (and aborted by caller on error)
+ * return 0 on success, < 0 on error
+ */
+int restore_capabilities(struct ckpt_capabilities *h, struct cred *new)
+{
+ int ret = do_restore_caps(h, new);
+
+ if (!ret)
+ ret = apply_securebits(h->securebits, new);

-error:
- abort_creds(new);
return ret;
}
+#endif /* CONFIG_CHECKPOINT */

/**
* capable - Determine if the current task has a superior capability in effect
diff --git a/security/commoncap.c b/security/commoncap.c
index e3097c0..892815b 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -893,24 +893,9 @@ 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 = apply_securebits(arg2, new);
+ if (error)
goto error;
- new->securebits = arg2;
goto changed;

case PR_GET_SECUREBITS:
--
1.6.0.4