Re: [PATCH 4.14 20/65] ptrace: reintroduce usage of subjective credentials in ptrace_has_cap()

From: Ben Hutchings
Date: Mon Apr 20 2020 - 10:15:23 EST

On Fri, 2020-01-24 at 08:38 +0100, Greg Kroah-Hartman wrote:
> On Thu, Jan 23, 2020 at 03:01:29PM -0800, Guenter Roeck wrote:
> > On Wed, Jan 22, 2020 at 10:29:05AM +0100, Greg Kroah-Hartman wrote:
> > > From: Christian Brauner <christian.brauner@xxxxxxxxxx>
> > >
> > > commit 6b3ad6649a4c75504edeba242d3fd36b3096a57f upstream.
[...]
> > > --- a/kernel/ptrace.c
> > > +++ b/kernel/ptrace.c
> > > @@ -258,12 +258,17 @@ static int ptrace_check_attach(struct ta
> > > return ret;
> > > }
> > >
> > > -static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode)
> > > +static bool ptrace_has_cap(const struct cred *cred, struct user_namespace *ns,
> > > + unsigned int mode)
> > > {
> > > + int ret;
> > > +
> > > if (mode & PTRACE_MODE_NOAUDIT)
> > > - return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE);
> > > + ret = security_capable(cred, ns, CAP_SYS_PTRACE);
> > > else
> > > - return has_ns_capability(current, ns, CAP_SYS_PTRACE);
> > > + ret = security_capable(cred, ns, CAP_SYS_PTRACE);
> > > +
> > > + return ret == 0;
> >
> > This results in
> > if (condition)
> > do_something;
> > else
> > do_the_same;
> >
> > Is that really correct ? The upstream patch calls security_capable()
> > with additional CAP_OPT_NOAUDIT vs. CAP_OPT_NONE parameter, which does
> > make sense. But I don't really see the benefit of the change above.
>
> Yeah, this is odd, and differs from the original version I applied to
> the staging queue.
>
> Sasha, you made this change to the patch, I'm guessing to make it build
> properly in 4.14? Should I just have dropped it from there instead?

To make this work properly, you would need to pick these for 4.14 as
well:

11c92f144bf3 apparmor: fix mediation of prlimit
(to avoid a conflict, but it's an important fix in its own right)

c1a85a00ea66 LSM: generalize flag passing to security_capable

I'm attaching a backport of the second commit.

Ben.

--
Ben Hutchings
Klipstein's 4th Law of Prototyping and Production:
A fail-safe circuit will destroy others.


From 7f3ab5da5b288244374b8ac53165a278b2399963 Mon Sep 17 00:00:00 2001
From: Micah Morton <mortonm@xxxxxxxxxxxx>
Date: Mon, 7 Jan 2019 16:10:53 -0800
Subject: [PATCH] LSM: generalize flag passing to security_capable

This patch provides a general mechanism for passing flags to the
security_capable LSM hook. It replaces the specific 'audit' flag that is
used to tell security_capable whether it should log an audit message for
the given capability check. The reason for generalizing this flag
passing is so we can add an additional flag that signifies whether
security_capable is being called by a setid syscall (which is needed by
the proposed SafeSetID LSM).

Signed-off-by: Micah Morton <mortonm@xxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: James Morris <james.morris@xxxxxxxxxxxxx>
[bwh: Backported to 4.14:
- Add the extra argument to security_capable() in ptrace_has_cap()
- Adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
include/linux/lsm_hooks.h | 8 +++++---
include/linux/security.h | 28 +++++++++++++-------------
kernel/capability.c | 22 +++++++++++---------
kernel/seccomp.c | 4 ++--
security/apparmor/capability.c | 14 ++++++-------
security/apparmor/include/capability.h | 2 +-
security/apparmor/ipc.c | 3 ++-
security/apparmor/lsm.c | 4 ++--
security/apparmor/resource.c | 2 +-
security/commoncap.c | 17 ++++++++--------
security/security.c | 14 +++++--------
security/selinux/hooks.c | 18 ++++++++---------
security/smack/smack_access.c | 2 +-
13 files changed, 71 insertions(+), 67 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index c9258124e417..3b957eff0a03 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1229,7 +1229,7 @@
* @cred contains the credentials to use.
* @ns contains the user namespace we want the capability in
* @cap contains the capability <include/linux/capability.h>.
- * @audit contains whether to write an audit message or not
+ * @opts contains options for the capable check <include/linux/security.h>
* Return 0 if the capability is granted for @tsk.
* @syslog:
* Check permission before accessing the kernel message ring or changing
@@ -1371,8 +1371,10 @@ union security_list_options {
const kernel_cap_t *effective,
const kernel_cap_t *inheritable,
const kernel_cap_t *permitted);
- int (*capable)(const struct cred *cred, struct user_namespace *ns,
- int cap, int audit);
+ int (*capable)(const struct cred *cred,
+ struct user_namespace *ns,
+ int cap,
+ unsigned int opts);
int (*quotactl)(int cmds, int type, int id, struct super_block *sb);
int (*quota_on)(struct dentry *dentry);
int (*syslog)(int type);
diff --git a/include/linux/security.h b/include/linux/security.h
index ce6265960d6c..61dc06f616d1 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -57,9 +57,12 @@ struct xattr;
struct xfrm_sec_ctx;
struct mm_struct;

+/* Default (no) options for the capable function */
+#define CAP_OPT_NONE 0x0
/* If capable should audit the security request */
-#define SECURITY_CAP_NOAUDIT 0
-#define SECURITY_CAP_AUDIT 1
+#define CAP_OPT_NOAUDIT BIT(1)
+/* If capable is being called by a setid function */
+#define CAP_OPT_INSETID BIT(2)

/* LSM Agnostic defines for sb_set_mnt_opts */
#define SECURITY_LSM_NATIVE_LABELS 1
@@ -75,7 +78,7 @@ enum lsm_event {

/* These functions are in security/commoncap.c */
extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
- int cap, int audit);
+ int cap, unsigned int opts);
extern int cap_settime(const struct timespec64 *ts, const struct timezone *tz);
extern int cap_ptrace_access_check(struct task_struct *child, unsigned int mode);
extern int cap_ptrace_traceme(struct task_struct *parent);
@@ -214,10 +217,10 @@ int security_capset(struct cred *new, const struct cred *old,
const kernel_cap_t *effective,
const kernel_cap_t *inheritable,
const kernel_cap_t *permitted);
-int security_capable(const struct cred *cred, struct user_namespace *ns,
- int cap);
-int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
- int cap);
+int security_capable(const struct cred *cred,
+ struct user_namespace *ns,
+ int cap,
+ unsigned int opts);
int security_quotactl(int cmds, int type, int id, struct super_block *sb);
int security_quota_on(struct dentry *dentry);
int security_syslog(int type);
@@ -477,14 +480,11 @@ static inline int security_capset(struct cred *new,
}

static inline int security_capable(const struct cred *cred,
- struct user_namespace *ns, int cap)
+ struct user_namespace *ns,
+ int cap,
+ unsigned int opts)
{
- return cap_capable(cred, ns, cap, SECURITY_CAP_AUDIT);
-}
-
-static inline int security_capable_noaudit(const struct cred *cred,
- struct user_namespace *ns, int cap) {
- return cap_capable(cred, ns, cap, SECURITY_CAP_NOAUDIT);
+ return cap_capable(cred, ns, cap, opts);
}

static inline int security_quotactl(int cmds, int type, int id,
diff --git a/kernel/capability.c b/kernel/capability.c
index 1e1c0236f55b..7718d7dcadc7 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -299,7 +299,7 @@ bool has_ns_capability(struct task_struct *t,
int ret;

rcu_read_lock();
- ret = security_capable(__task_cred(t), ns, cap);
+ ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NONE);
rcu_read_unlock();

return (ret == 0);
@@ -340,7 +340,7 @@ bool has_ns_capability_noaudit(struct task_struct *t,
int ret;

rcu_read_lock();
- ret = security_capable_noaudit(__task_cred(t), ns, cap);
+ ret = security_capable(__task_cred(t), ns, cap, CAP_OPT_NOAUDIT);
rcu_read_unlock();

return (ret == 0);
@@ -363,7 +363,9 @@ bool has_capability_noaudit(struct task_struct *t, int cap)
return has_ns_capability_noaudit(t, &init_user_ns, cap);
}

-static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
+static bool ns_capable_common(struct user_namespace *ns,
+ int cap,
+ unsigned int opts)
{
int capable;

@@ -372,8 +374,7 @@ static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
BUG();
}

- capable = audit ? security_capable(current_cred(), ns, cap) :
- security_capable_noaudit(current_cred(), ns, cap);
+ capable = security_capable(current_cred(), ns, cap, opts);
if (capable == 0) {
current->flags |= PF_SUPERPRIV;
return true;
@@ -394,7 +395,7 @@ static bool ns_capable_common(struct user_namespace *ns, int cap, bool audit)
*/
bool ns_capable(struct user_namespace *ns, int cap)
{
- return ns_capable_common(ns, cap, true);
+ return ns_capable_common(ns, cap, CAP_OPT_NONE);
}
EXPORT_SYMBOL(ns_capable);

@@ -412,7 +413,7 @@ EXPORT_SYMBOL(ns_capable);
*/
bool ns_capable_noaudit(struct user_namespace *ns, int cap)
{
- return ns_capable_common(ns, cap, false);
+ return ns_capable_common(ns, cap, CAP_OPT_NOAUDIT);
}
EXPORT_SYMBOL(ns_capable_noaudit);

@@ -448,10 +449,11 @@ EXPORT_SYMBOL(capable);
bool file_ns_capable(const struct file *file, struct user_namespace *ns,
int cap)
{
+
if (WARN_ON_ONCE(!cap_valid(cap)))
return false;

- if (security_capable(file->f_cred, ns, cap) == 0)
+ if (security_capable(file->f_cred, ns, cap, CAP_OPT_NONE) == 0)
return true;

return false;
@@ -500,10 +502,12 @@ bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns)
{
int ret = 0; /* An absent tracer adds no restrictions */
const struct cred *cred;
+
rcu_read_lock();
cred = rcu_dereference(tsk->ptracer_cred);
if (cred)
- ret = security_capable_noaudit(cred, ns, CAP_SYS_PTRACE);
+ ret = security_capable(cred, ns, CAP_SYS_PTRACE,
+ CAP_OPT_NOAUDIT);
rcu_read_unlock();
return (ret == 0);
}
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 075e344a87c3..791f56869324 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -383,8 +383,8 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
* behavior of privileged children.
*/
if (!task_no_new_privs(current) &&
- security_capable_noaudit(current_cred(), current_user_ns(),
- CAP_SYS_ADMIN) != 0)
+ security_capable(current_cred(), current_user_ns(),
+ CAP_SYS_ADMIN, CAP_OPT_NOAUDIT) != 0)
return ERR_PTR(-EACCES);

/* Allocate a new seccomp_filter */
diff --git a/security/apparmor/capability.c b/security/apparmor/capability.c
index 67e347192a55..4ee296ec2f11 100644
--- a/security/apparmor/capability.c
+++ b/security/apparmor/capability.c
@@ -110,13 +110,13 @@ static int audit_caps(struct common_audit_data *sa, struct aa_profile *profile,
* profile_capable - test if profile allows use of capability @cap
* @profile: profile being enforced (NOT NULL, NOT unconfined)
* @cap: capability to test if allowed
- * @audit: whether an audit record should be generated
+ * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
* @sa: audit data (MAY BE NULL indicating no auditing)
*
* Returns: 0 if allowed else -EPERM
*/
-static int profile_capable(struct aa_profile *profile, int cap, int audit,
- struct common_audit_data *sa)
+static int profile_capable(struct aa_profile *profile, int cap,
+ unsigned int opts, struct common_audit_data *sa)
{
int error;

@@ -126,7 +126,7 @@ static int profile_capable(struct aa_profile *profile, int cap, int audit,
else
error = -EPERM;

- if (audit == SECURITY_CAP_NOAUDIT) {
+ if (opts & CAP_OPT_NOAUDIT) {
if (!COMPLAIN_MODE(profile))
return error;
/* audit the cap request in complain mode but note that it
@@ -142,13 +142,13 @@ static int profile_capable(struct aa_profile *profile, int cap, int audit,
* aa_capable - test permission to use capability
* @label: label being tested for capability (NOT NULL)
* @cap: capability to be tested
- * @audit: whether an audit record should be generated
+ * @opts: CAP_OPT_NOAUDIT bit determines whether audit record is generated
*
* Look up capability in profile capability set.
*
* Returns: 0 on success, or else an error code.
*/
-int aa_capable(struct aa_label *label, int cap, int audit)
+int aa_capable(struct aa_label *label, int cap, unsigned int opts)
{
struct aa_profile *profile;
int error = 0;
@@ -156,7 +156,7 @@ int aa_capable(struct aa_label *label, int cap, int audit)

sa.u.cap = cap;
error = fn_for_each_confined(label, profile,
- profile_capable(profile, cap, audit, &sa));
+ profile_capable(profile, cap, opts, &sa));

return error;
}
diff --git a/security/apparmor/include/capability.h b/security/apparmor/include/capability.h
index e0304e2aeb7f..1b3663b6ab12 100644
--- a/security/apparmor/include/capability.h
+++ b/security/apparmor/include/capability.h
@@ -40,7 +40,7 @@ struct aa_caps {

extern struct aa_sfs_entry aa_sfs_entry_caps[];

-int aa_capable(struct aa_label *label, int cap, int audit);
+int aa_capable(struct aa_label *label, int cap, unsigned int opts);

static inline void aa_free_cap_rules(struct aa_caps *caps)
{
diff --git a/security/apparmor/ipc.c b/security/apparmor/ipc.c
index 586facd35f7c..b4ed35233b1a 100644
--- a/security/apparmor/ipc.c
+++ b/security/apparmor/ipc.c
@@ -107,7 +107,8 @@ static int profile_tracer_perm(struct aa_profile *tracer,
aad(sa)->label = &tracer->label;
aad(sa)->peer = tracee;
aad(sa)->request = 0;
- aad(sa)->error = aa_capable(&tracer->label, CAP_SYS_PTRACE, 1);
+ aad(sa)->error = aa_capable(&tracer->label, CAP_SYS_PTRACE,
+ CAP_OPT_NONE);

return aa_audit(AUDIT_APPARMOR_AUTO, tracer, sa, audit_ptrace_cb);
}
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 4f08023101f3..c95279d61db3 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -167,14 +167,14 @@ static int apparmor_capget(struct task_struct *target, kernel_cap_t *effective,
}

static int apparmor_capable(const struct cred *cred, struct user_namespace *ns,
- int cap, int audit)
+ int cap, unsigned int opts)
{
struct aa_label *label;
int error = 0;

label = aa_get_newest_cred_label(cred);
if (!unconfined(label))
- error = aa_capable(label, cap, audit);
+ error = aa_capable(label, cap, opts);
aa_put_label(label);

return error;
diff --git a/security/apparmor/resource.c b/security/apparmor/resource.c
index 5d4219709d44..e0268424e11c 100644
--- a/security/apparmor/resource.c
+++ b/security/apparmor/resource.c
@@ -124,7 +124,7 @@ int aa_task_setrlimit(struct aa_label *label, struct task_struct *task,
*/

if (label != peer &&
- aa_capable(label, CAP_SYS_RESOURCE, SECURITY_CAP_NOAUDIT) != 0)
+ aa_capable(label, CAP_SYS_RESOURCE, CAP_OPT_NOAUDIT) != 0)
error = fn_for_each(label, profile,
audit_resource(profile, resource,
new_rlim->rlim_max, peer,
diff --git a/security/commoncap.c b/security/commoncap.c
index ae26ef006988..d54fd36b5d80 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -69,7 +69,7 @@ static void warn_setuid_and_fcaps_mixed(const char *fname)
* kernel's capable() and has_capability() returns 1 for this case.
*/
int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
- int cap, int audit)
+ int cap, unsigned int opts)
{
struct user_namespace *ns = targ_ns;

@@ -223,12 +223,11 @@ int cap_capget(struct task_struct *target, kernel_cap_t *effective,
*/
static inline int cap_inh_is_capped(void)
{
-
/* they are so limited unless the current task has the CAP_SETPCAP
* capability
*/
if (cap_capable(current_cred(), current_cred()->user_ns,
- CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
+ CAP_SETPCAP, CAP_OPT_NONE) == 0)
return 0;
return 1;
}
@@ -1145,8 +1144,9 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
|| ((old->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
|| (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
|| (cap_capable(current_cred(),
- current_cred()->user_ns, CAP_SETPCAP,
- SECURITY_CAP_AUDIT) != 0) /*[4]*/
+ current_cred()->user_ns,
+ CAP_SETPCAP,
+ CAP_OPT_NONE) != 0) /*[4]*/
/*
* [1] no changing of bits that are locked
* [2] no unlocking of locks
@@ -1241,9 +1241,10 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
{
int cap_sys_admin = 0;

- if (cap_capable(current_cred(), &init_user_ns, CAP_SYS_ADMIN,
- SECURITY_CAP_NOAUDIT) == 0)
+ if (cap_capable(current_cred(), &init_user_ns,
+ CAP_SYS_ADMIN, CAP_OPT_NOAUDIT) == 0)
cap_sys_admin = 1;
+
return cap_sys_admin;
}

@@ -1262,7 +1263,7 @@ int cap_mmap_addr(unsigned long addr)

if (addr < dac_mmap_min_addr) {
ret = cap_capable(current_cred(), &init_user_ns, CAP_SYS_RAWIO,
- SECURITY_CAP_AUDIT);
+ CAP_OPT_NONE);
/* set PF_SUPERPRIV if it turns out we allow the low mmap */
if (ret == 0)
current->flags |= PF_SUPERPRIV;
diff --git a/security/security.c b/security/security.c
index 4fbe4e495c02..4e3e697d419b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -273,16 +273,12 @@ int security_capset(struct cred *new, const struct cred *old,
effective, inheritable, permitted);
}

-int security_capable(const struct cred *cred, struct user_namespace *ns,
- int cap)
+int security_capable(const struct cred *cred,
+ struct user_namespace *ns,
+ int cap,
+ unsigned int opts)
{
- return call_int_hook(capable, 0, cred, ns, cap, SECURITY_CAP_AUDIT);
-}
-
-int security_capable_noaudit(const struct cred *cred, struct user_namespace *ns,
- int cap)
-{
- return call_int_hook(capable, 0, cred, ns, cap, SECURITY_CAP_NOAUDIT);
+ return call_int_hook(capable, 0, cred, ns, cap, opts);
}

int security_quotactl(int cmds, int type, int id, struct super_block *sb)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 5f7bfc65c446..f2571d1072b8 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1738,7 +1738,7 @@ static inline u32 signal_to_av(int sig)

/* Check whether a task is allowed to use a capability. */
static int cred_has_capability(const struct cred *cred,
- int cap, int audit, bool initns)
+ int cap, unsigned int opts, bool initns)
{
struct common_audit_data ad;
struct av_decision avd;
@@ -1765,7 +1765,7 @@ static int cred_has_capability(const struct cred *cred,
}

rc = avc_has_perm_noaudit(sid, sid, sclass, av, 0, &avd);
- if (audit == SECURITY_CAP_AUDIT) {
+ if (!(opts & CAP_OPT_NOAUDIT)) {
int rc2 = avc_audit(sid, sid, sclass, av, &avd, rc, &ad, 0);
if (rc2)
return rc2;
@@ -2242,9 +2242,9 @@ static int selinux_capset(struct cred *new, const struct cred *old,
*/

static int selinux_capable(const struct cred *cred, struct user_namespace *ns,
- int cap, int audit)
+ int cap, unsigned int opts)
{
- return cred_has_capability(cred, cap, audit, ns == &init_user_ns);
+ return cred_has_capability(cred, cap, opts, ns == &init_user_ns);
}

static int selinux_quotactl(int cmds, int type, int id, struct super_block *sb)
@@ -2315,7 +2315,7 @@ static int selinux_vm_enough_memory(struct mm_struct *mm, long pages)
int rc, cap_sys_admin = 0;

rc = cred_has_capability(current_cred(), CAP_SYS_ADMIN,
- SECURITY_CAP_NOAUDIT, true);
+ CAP_OPT_NOAUDIT, true);
if (rc == 0)
cap_sys_admin = 1;

@@ -3173,11 +3173,11 @@ static int selinux_inode_setotherxattr(struct dentry *dentry, const char *name)
static bool has_cap_mac_admin(bool audit)
{
const struct cred *cred = current_cred();
- int cap_audit = audit ? SECURITY_CAP_AUDIT : SECURITY_CAP_NOAUDIT;
+ unsigned int opts = audit ? CAP_OPT_NONE : CAP_OPT_NOAUDIT;

- if (cap_capable(cred, &init_user_ns, CAP_MAC_ADMIN, cap_audit))
+ if (cap_capable(cred, &init_user_ns, CAP_MAC_ADMIN, opts))
return false;
- if (cred_has_capability(cred, CAP_MAC_ADMIN, cap_audit, true))
+ if (cred_has_capability(cred, CAP_MAC_ADMIN, opts, true))
return false;
return true;
}
@@ -3556,7 +3556,7 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
case KDSKBENT:
case KDSKBSENT:
error = cred_has_capability(cred, CAP_SYS_TTY_CONFIG,
- SECURITY_CAP_AUDIT, true);
+ CAP_OPT_NONE, true);
break;

/* default case assumes that the command will go
diff --git a/security/smack/smack_access.c b/security/smack/smack_access.c
index a9c20821a726..378a870fdb2f 100644
--- a/security/smack/smack_access.c
+++ b/security/smack/smack_access.c
@@ -642,7 +642,7 @@ bool smack_privileged(int cap)
return true;

rc = cap_capable(current_cred(), &init_user_ns, cap,
- SECURITY_CAP_AUDIT);
+ CAP_OPT_NONE);
if (rc)
return false;

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