Quoting Eric W. Biederman ([email protected]): > "Serge E. Hallyn" <[email protected]> writes: > > > So i was thinking about how to safely but incrementally introduce > > targeted capabilities - which we decided was a prereq to making VFS > > handle user namespaces - and the following seemed doable. My main > > motivations were (in order): > > > > 1. don't make any unconverted capable() checks unsafe > > 2. minimize performance impact on non-container case > > 3. minimize performance impact on containers > > My motivation is a bit different. I would like to get to the > unprivileged creation of new namespaces. It looks like this gets us > 90% of the way there, with only potential uid confusion issues left.
Yup, that was actually what I was thinking about last night when I decided to give it a shot :) IMO, my patch + a dummy version of user_namespaces for vfs (done in a clean way that can be an incremental step toward full vfs userns support - which I haven't yet thought through) is enough to give you safe fully unprivileged containers. Now with the API I have, you'd have a program with either setuid-root or cap_sys_admin,cap_setpcap=pe which does the prctl and the unshares, but it would theoretically be safe to hand that program to unprivileged users. > I still need to handle getting all caps after creation but otherwise I > think I have a good starter patch that achieves all of your goals. Well in my patch we don't need to clear out the bounding set, or set SETUID_NOROOT - so running a setuid root program or becoming root should still give you capabilities! They'll just be targeted at your container. I really think this is what you need. > Of course kill_permission needs the checks you have suggested as well. Ok, I can't look at your patch in detail right now and don't quite get where you're going with a quick glance, so will look in closer detail later. Will also think about a way to get "just-enough" vfs userns support to completely give you what you need for privileged users in unprivileged containers. -serge > >From db104af741b5f0a2f128688905498cae68fbbde2 Mon Sep 17 00:00:00 2001 > From: Eric W. Biederman <[email protected]> > Date: Wed, 6 Jan 2010 08:26:21 -0800 > Subject: [PATCH] security: Make capabilities relative to the user namespace. > > - Introduce ns_capable to test for a capability in a non-default > user namespace. > - Teach cap_capable to handle capabilities in a non-default > user namespace. > > Signed-off-by: Eric W. Biederman <[email protected]> > --- > include/linux/capability.h | 6 ++++-- > include/linux/security.h | 12 +++++++----- > kernel/capability.c | 22 ++++++++++++++++++++-- > security/commoncap.c | 40 +++++++++++++++++++++++++++++++++------- > security/security.c | 12 ++++++------ > security/selinux/hooks.c | 14 +++++++++----- > 6 files changed, 79 insertions(+), 27 deletions(-) > > diff --git a/include/linux/capability.h b/include/linux/capability.h > index 39e5ff5..89572b2 100644 > --- a/include/linux/capability.h > +++ b/include/linux/capability.h > @@ -544,7 +544,7 @@ extern const kernel_cap_t __cap_init_eff_set; > * > * Note that this does not set PF_SUPERPRIV on the task. > */ > -#define has_capability(t, cap) (security_real_capable((t), (cap)) == 0) > +#define has_capability(t, cap) (security_real_capable((t), &init_user_ns, > (cap)) == 0) > > /** > * has_capability_noaudit - Determine if a task has a superior capability > available (unaudited) > @@ -558,9 +558,11 @@ extern const kernel_cap_t __cap_init_eff_set; > * Note that this does not set PF_SUPERPRIV on the task. > */ > #define has_capability_noaudit(t, cap) \ > - (security_real_capable_noaudit((t), (cap)) == 0) > + (security_real_capable_noaudit((t), &init_user_ns, (cap)) == 0) > > +struct user_namespace; > extern int capable(int cap); > +extern int ns_capable(struct user_namespace *ns, int cap); > > /* audit system wants to get cap info from files as well */ > struct dentry; > diff --git a/include/linux/security.h b/include/linux/security.h > index 2c627d3..f44932f 100644 > --- a/include/linux/security.h > +++ b/include/linux/security.h > @@ -45,13 +45,14 @@ > > struct ctl_table; > struct audit_krule; > +struct user_namespace; > > /* > * These functions are in security/capability.c and are used > * as the default capabilities functions > */ > extern int cap_capable(struct task_struct *tsk, const struct cred *cred, > - int cap, int audit); > + struct user_namespace *ns, int cap, int audit); > extern int cap_settime(struct timespec *ts, 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); > @@ -1327,6 +1328,7 @@ static inline void security_free_mnt_opts(struct > security_mnt_opts *opts) > * credentials. > * @tsk contains the task_struct for the process. > * @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: Whether to write an audit message or not > * Return 0 if the capability is granted for @tsk. > @@ -1457,7 +1459,7 @@ struct security_operations { > const kernel_cap_t *inheritable, > const kernel_cap_t *permitted); > int (*capable) (struct task_struct *tsk, const struct cred *cred, > - int cap, int audit); > + struct user_namespace *ns, int cap, int audit); > int (*acct) (struct file *file); > int (*sysctl) (struct ctl_table *table, int op); > int (*quotactl) (int cmds, int type, int id, struct super_block *sb); > @@ -1754,9 +1756,9 @@ 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(int cap); > -int security_real_capable(struct task_struct *tsk, int cap); > -int security_real_capable_noaudit(struct task_struct *tsk, int cap); > +int security_capable(struct user_namespace *ns, int cap); > +int security_real_capable(struct task_struct *tsk, struct user_namespace > *ns, int cap); > +int security_real_capable_noaudit(struct task_struct *tsk, struct > user_namespace *ns, int cap); > int security_acct(struct file *file); > int security_sysctl(struct ctl_table *table, int op); > int security_quotactl(int cmds, int type, int id, struct super_block *sb); > diff --git a/kernel/capability.c b/kernel/capability.c > index 7f876e6..63dcf53 100644 > --- a/kernel/capability.c > +++ b/kernel/capability.c > @@ -14,6 +14,7 @@ > #include <linux/security.h> > #include <linux/syscalls.h> > #include <linux/pid_namespace.h> > +#include <linux/user_namespace.h> > #include <asm/uaccess.h> > #include "cred-internals.h" > > @@ -302,15 +303,32 @@ error: > */ > int capable(int cap) > { > + return ns_capable(&init_user_ns, cap); > +} > +EXPORT_SYMBOL(capable); > + > +/** > + * ns_capable - Determine if the current task has a superior capability in > effect > + * @ns: The usernamespace we want the capability in > + * @cap: The capability to be tested for > + * > + * Return true if the current task has the given superior capability > currently > + * available for use, false if not. > + * > + * This sets PF_SUPERPRIV on the task if the capability is available on the > + * assumption that it's about to be used. > + */ > +int ns_capable(struct user_namespace *ns, int cap) > +{ > if (unlikely(!cap_valid(cap))) { > printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap); > BUG(); > } > > - if (security_capable(cap) == 0) { > + if (security_capable(ns, cap) == 0) { > current->flags |= PF_SUPERPRIV; > return 1; > } > return 0; > } > -EXPORT_SYMBOL(capable); > +EXPORT_SYMBOL(ns_capable); > diff --git a/security/commoncap.c b/security/commoncap.c > index 34500e3..ffde5be 100644 > --- a/security/commoncap.c > +++ b/security/commoncap.c > @@ -27,6 +27,7 @@ > #include <linux/sched.h> > #include <linux/prctl.h> > #include <linux/securebits.h> > +#include <linux/user_namespace.h> > > /* > * If a non-root user executes a setuid-root binary in > @@ -68,6 +69,7 @@ EXPORT_SYMBOL(cap_netlink_recv); > * cap_capable - Determine whether a task has a particular effective > capability > * @tsk: The task to query > * @cred: The credentials to use > + * @ns: The user namespace in which we need the capability > * @cap: The capability to check for > * @audit: Whether to write an audit message or not > * > @@ -79,10 +81,32 @@ EXPORT_SYMBOL(cap_netlink_recv); > * cap_has_capability() returns 0 when a task has a capability, but the > * kernel's capable() and has_capability() returns 1 for this case. > */ > -int cap_capable(struct task_struct *tsk, const struct cred *cred, int cap, > - int audit) > +int cap_capable(struct task_struct *tsk, const struct cred *cred, > + struct user_namespace *targ_ns, int cap, int audit) > { > - return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM; > + for (;;) { > + /* Do we have the necessary capabilities? */ > + if (targ_ns == cred->user->user_ns) > + return cap_raised(cred->cap_effective, cap) ? 0 : > -EPERM; > + > + /* The creator of the user namespace has all caps. */ > + if (targ_ns->creator == cred->user) > + return 0; > + > + /* Have we tried all of the parent namespaces? */ > + if (targ_ns == &init_user_ns) > + return -EPERM; > + > + /* If you have the capability in a parent user ns you have it > + * in the over all children user namespaces as well, so see > + * if this process has the capability in the parent user > + * namespace. > + */ > + targ_ns = targ_ns->creator->user_ns; > + } > + > + /* We never get here */ > + return -EPERM; > } > > /** > @@ -177,7 +201,8 @@ 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, current_cred(), CAP_SETPCAP, > + if (cap_capable(current, current_cred(), > + current_cred()->user->user_ns, CAP_SETPCAP, > SECURITY_CAP_AUDIT) == 0) > return 0; > return 1; > @@ -832,7 +857,8 @@ int cap_task_prctl(int option, unsigned long arg2, > unsigned long arg3, > & (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, > + || (cap_capable(current, current_cred(), > + current_cred()->user->user_ns, CAP_SETPCAP, > SECURITY_CAP_AUDIT) != 0) /*[4]*/ > /* > * [1] no changing of bits that are locked > @@ -910,7 +936,7 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages) > { > int cap_sys_admin = 0; > > - if (cap_capable(current, current_cred(), CAP_SYS_ADMIN, > + if (cap_capable(current, current_cred(), &init_user_ns, CAP_SYS_ADMIN, > SECURITY_CAP_NOAUDIT) == 0) > cap_sys_admin = 1; > return __vm_enough_memory(mm, pages, cap_sys_admin); > @@ -937,7 +963,7 @@ int cap_file_mmap(struct file *file, unsigned long > reqprot, > int ret = 0; > > if (addr < dac_mmap_min_addr) { > - ret = cap_capable(current, current_cred(), CAP_SYS_RAWIO, > + ret = cap_capable(current, current_cred(), &init_user_ns, > CAP_SYS_RAWIO, > SECURITY_CAP_AUDIT); > /* set PF_SUPERPRIV if it turns out we allow the low mmap */ > if (ret == 0) > diff --git a/security/security.c b/security/security.c > index 24e060b..ad75427 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -155,30 +155,30 @@ int security_capset(struct cred *new, const struct cred > *old, > effective, inheritable, permitted); > } > > -int security_capable(int cap) > +int security_capable(struct user_namespace *ns, int cap) > { > - return security_ops->capable(current, current_cred(), cap, > + return security_ops->capable(current, current_cred(), ns, cap, > SECURITY_CAP_AUDIT); > } > > -int security_real_capable(struct task_struct *tsk, int cap) > +int security_real_capable(struct task_struct *tsk, struct user_namespace > *ns, int cap) > { > const struct cred *cred; > int ret; > > cred = get_task_cred(tsk); > - ret = security_ops->capable(tsk, cred, cap, SECURITY_CAP_AUDIT); > + ret = security_ops->capable(tsk, cred, ns, cap, SECURITY_CAP_AUDIT); > put_cred(cred); > return ret; > } > > -int security_real_capable_noaudit(struct task_struct *tsk, int cap) > +int security_real_capable_noaudit(struct task_struct *tsk, struct > user_namespace *ns, int cap) > { > const struct cred *cred; > int ret; > > cred = get_task_cred(tsk); > - ret = security_ops->capable(tsk, cred, cap, SECURITY_CAP_NOAUDIT); > + ret = security_ops->capable(tsk, cred, ns, cap, SECURITY_CAP_NOAUDIT); > put_cred(cred); > return ret; > } > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index bd77a2b..a69f97d 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -76,6 +76,7 @@ > #include <linux/selinux.h> > #include <linux/mutex.h> > #include <linux/posix-timers.h> > +#include <linux/user_namespace.h> > > #include "avc.h" > #include "objsec.h" > @@ -1480,6 +1481,7 @@ static int current_has_perm(const struct task_struct > *tsk, > /* Check whether a task is allowed to use a capability. */ > static int task_has_capability(struct task_struct *tsk, > const struct cred *cred, > + struct user_namespace *ns, > int cap, int audit) > { > struct common_audit_data ad; > @@ -1927,15 +1929,15 @@ static int selinux_capset(struct cred *new, const > struct cred *old, > */ > > static int selinux_capable(struct task_struct *tsk, const struct cred *cred, > - int cap, int audit) > + struct user_namespace *ns, int cap, int audit) > { > int rc; > > - rc = cap_capable(tsk, cred, cap, audit); > + rc = cap_capable(tsk, cred, ns, cap, audit); > if (rc) > return rc; > > - return task_has_capability(tsk, cred, cap, audit); > + return task_has_capability(tsk, cred, ns, cap, audit); > } > > static int selinux_sysctl_get_sid(ctl_table *table, u16 tclass, u32 *sid) > @@ -2091,7 +2093,8 @@ static int selinux_vm_enough_memory(struct mm_struct > *mm, long pages) > { > int rc, cap_sys_admin = 0; > > - rc = selinux_capable(current, current_cred(), CAP_SYS_ADMIN, > + rc = selinux_capable(current, current_cred(), > + &init_user_ns, CAP_SYS_ADMIN, > SECURITY_CAP_NOAUDIT); > if (rc == 0) > cap_sys_admin = 1; > @@ -2889,7 +2892,8 @@ static int selinux_inode_getsecurity(const struct inode > *inode, const char *name > * and lack of permission just means that we fall back to the > * in-core context value, not a denial. > */ > - error = selinux_capable(current, current_cred(), CAP_MAC_ADMIN, > + error = selinux_capable(current, current_cred(), > + &init_user_ns, CAP_MAC_ADMIN, > SECURITY_CAP_NOAUDIT); > if (!error) > error = security_sid_to_context_force(isec->sid, &context, > -- > 1.6.5.2.143.g8cc62 _______________________________________________ Containers mailing list [email protected] https://lists.linux-foundation.org/mailman/listinfo/containers _______________________________________________ Devel mailing list [email protected] https://openvz.org/mailman/listinfo/devel
