[PATCH v2] LSM: generalize flag passing to security_capable
Micah Morton
mortonm at chromium.org
Tue Jan 8 00:10:59 UTC 2019
On Mon, Jan 7, 2019 at 3:13 PM Kees Cook <keescook at chromium.org> wrote:
>
> On Tue, Dec 18, 2018 at 2:37 PM <mortonm at chromium.org> wrote:
> >
> > From: Micah Morton <mortonm at chromium.org>
> >
> > 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 at chromium.org>
> > ---
> > Changes since the last patch: Changed the code to use a bitmask instead
> > of a struct to represent the options passed to security_capable.
>
> FWIW, I too prefer this v2 patch. I don't see a reason to keep an
> "option-ified" function around if it's been generalized into a
> bitfield argument.
>
> > 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/commoncap.c | 17 ++++++++--------
> > security/security.c | 14 +++++--------
> > security/selinux/hooks.c | 16 +++++++--------
> > security/smack/smack_access.c | 2 +-
> > 12 files changed, 69 insertions(+), 65 deletions(-)
> >
> > diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> > index aaeb7fa24dc4..ef955a44a782 100644
> > --- a/include/linux/lsm_hooks.h
> > +++ b/include/linux/lsm_hooks.h
> > @@ -1270,7 +1270,7 @@
> > * @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
> > @@ -1446,8 +1446,10 @@ 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 d170a5b031f3..038e6779948c 100644
> > --- a/include/linux/security.h
> > +++ b/include/linux/security.h
> > @@ -54,9 +54,12 @@ struct xattr;
> > struct xfrm_sec_ctx;
> > struct mm_struct;
> >
> > +/* Default (no) options for the capable function */
> > +#define SECURITY_CAP_DEFAULT 0x0
>
> bikeshed: maybe we should call this CAP_OPT_* ? (Then this might be
> CAP_OPT_NONE?)
I agree, I like those names better.
>
> > /* If capable should audit the security request */
> > -#define SECURITY_CAP_NOAUDIT 0
> > -#define SECURITY_CAP_AUDIT 1
> > +#define SECURITY_CAP_NOAUDIT 0x01
> > +/* If capable is being called by a setid function */
> > +#define SECURITY_CAP_INSETID 0x02
>
> For the 1 and 2 case, can you use BIT(0) and BIT(1) instead? This
> makes it clear this is a bitfield here (and does all the type magic
> for higher-order bits if we ever get ther).
Done.
>
> > /* LSM Agnostic defines for sb_set_mnt_opts */
> > #define SECURITY_LSM_NATIVE_LABELS 1
> > @@ -72,7 +75,7 @@ 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);
> > @@ -233,10 +236,10 @@ 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);
> > @@ -492,14 +495,11 @@ 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..454576743b1b 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, SECURITY_CAP_DEFAULT);
> > rcu_read_unlock();
> >
> > return (ret == 0);
> > @@ -340,7 +340,7 @@ bool has_ns_capability_noaudit(struct task_struct *t,
>
> One argument for _keeping_ the _noaudit() function as in v3 is that
> keeping this one but removing the other seems inconsistent.
Hmm yeah. Removing the function still seems like the lesser evil to me
but I see what you mean.
>
> > int ret;
> >
> > rcu_read_lock();
> > - ret = security_capable_noaudit(__task_cred(t), ns, cap);
> > + ret = security_capable(__task_cred(t), ns, cap, SECURITY_CAP_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, SECURITY_CAP_DEFAULT);
> > }
> > 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, SECURITY_CAP_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, SECURITY_CAP_DEFAULT) == 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,
> > + SECURITY_CAP_NOAUDIT);
> > rcu_read_unlock();
> > return (ret == 0);
> > }
> > diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> > index f2ae2324c232..ddf615eb1bf7 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, SECURITY_CAP_NOAUDIT) != 0)
> > return ERR_PTR(-EACCES);
> >
> > /* Allocate a new seccomp_filter */
> > diff --git a/security/apparmor/capability.c b/security/apparmor/capability.c
> > index 253ef6e9d445..0f6dca54b66e 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: SECURITY_CAP_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 & SECURITY_CAP_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: SECURITY_CAP_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 527ea1557120..4a1da2313162 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,
> > + SECURITY_CAP_DEFAULT);
> >
> > return aa_audit(AUDIT_APPARMOR_AUTO, tracer, sa, audit_ptrace_cb);
> > }
> > diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> > index 42446a216f3b..0bd817084fc1 100644
> > --- a/security/apparmor/lsm.c
> > +++ b/security/apparmor/lsm.c
> > @@ -176,14 +176,14 @@ 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/commoncap.c b/security/commoncap.c
> > index 232db019f051..3d8609192e17 100644
> > --- a/security/commoncap.c
> > +++ b/security/commoncap.c
> > @@ -68,7 +68,7 @@ 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;
> >
> > @@ -222,12 +222,11 @@ 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, SECURITY_CAP_DEFAULT) == 0)
> > return 0;
> > return 1;
> > }
> > @@ -1208,8 +1207,9 @@ 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,
> > + SECURITY_CAP_DEFAULT) != 0) /*[4]*/
> > /*
> > * [1] no changing of bits that are locked
> > * [2] no unlocking of locks
> > @@ -1304,9 +1304,10 @@ 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, SECURITY_CAP_NOAUDIT) == 0)
> > cap_sys_admin = 1;
> > +
> > return cap_sys_admin;
> > }
> >
> > @@ -1325,7 +1326,7 @@ 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);
> > + SECURITY_CAP_DEFAULT);
> > /* 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 d670136dda2c..d2334697797a 100644
> > --- a/security/security.c
> > +++ b/security/security.c
> > @@ -294,16 +294,12 @@ 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 a67459eb62d5..a4b2e49213de 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -1769,7 +1769,7 @@ 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;
> > @@ -1796,7 +1796,7 @@ static int cred_has_capability(const struct cred *cred,
> >
> > rc = avc_has_perm_noaudit(&selinux_state,
> > sid, sid, sclass, av, 0, &avd);
> > - if (audit == SECURITY_CAP_AUDIT) {
> > + if (!(opts & SECURITY_CAP_NOAUDIT)) {
> > int rc2 = avc_audit(&selinux_state,
> > sid, sid, sclass, av, &avd, rc, &ad, 0);
> > if (rc2)
> > @@ -2316,9 +2316,9 @@ 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)
> > @@ -3245,11 +3245,11 @@ static int selinux_inode_getattr(const struct path *path)
> > 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 ? SECURITY_CAP_DEFAULT : SECURITY_CAP_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;
> > }
> > @@ -3649,7 +3649,7 @@ 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);
> > + SECURITY_CAP_DEFAULT, 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 9a4c0ad46518..fac2a21aa7d4 100644
> > --- a/security/smack/smack_access.c
> > +++ b/security/smack/smack_access.c
> > @@ -640,7 +640,7 @@ bool smack_privileged_cred(int cap, const struct cred *cred)
> > struct smack_known_list_elem *sklep;
> > int rc;
> >
> > - rc = cap_capable(cred, &init_user_ns, cap, SECURITY_CAP_AUDIT);
> > + rc = cap_capable(cred, &init_user_ns, cap, SECURITY_CAP_DEFAULT);
> > if (rc)
> > return false;
> >
> > --
> > 2.20.0.405.gbc1bbc6f85-goog
> >
>
> Otherwise, this looks fine to me.
>
> Reviewed-by: Kees Cook <keescook at chromium.org>
>
> James, Stephen, thoughts?
>
> --
> Kees Cook
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