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Date: Fri, 27 Jun 2008 16:06:16 -0500
From: "Serge E. Hallyn" <serue@...ibm.com>
To: "Andrew G. Morgan" <morgan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
David Howells <dhowells@...hat.com>,
"Serge E. Hallyn" <serue@...ibm.com>,
lkml <linux-kernel@...r.kernel.org>,
Linux Security Modules List
<linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 3/4] security: filesystem capabilities refactor kernel
code
Quoting Andrew G. Morgan (morgan@...nel.org):
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> More optimal kernel locking for filesystem capability support.
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.2.6 (GNU/Linux)
>
> iD8DBQFIY1gi+bHCR3gb8jsRAuqYAJ0c5Vw3WVHJFcSBZoHGhAEDR1RSDQCfUSgy
> m6bfMSlHRkEIulIxqp96t3E=
> =Xs/z
> -----END PGP SIGNATURE-----
> From 73bb5a039e95b9d150c74feaf5824a1f761fb718 Mon Sep 17 00:00:00 2001
> From: Andrew G. Morgan <morgan@...nel.org>
> Date: Wed, 25 Jun 2008 23:30:44 -0700
> Subject: [PATCH] Refactor filesystem capability support in main kernel.
>
> To date, we've tried hard to confine filesystem support for capabilities
> to the security modules. This has left a lot of the code in
> kernel/capability.c in a state where it looks like it supports something
> that filesystem support for capabilities actually suppresses when the
> LSM security/commmoncap.c code runs. What is left is a lot of code that
> uses sub-optimal locking in the main kernel. With this change we refactor
> the main kernel code and make it explicit which locks are needed and that
> the only remaining kernel races in this area are associated with
> non-filesystem capability code.
>
> Signed-off-by: Andrew G. Morgan <morgan@...nel.org>
No changelog, so I assume this is essentially the same patch as I
acked+tested on Jun 23.
Acked-by: Serge Hallyn <serue@...ibm.com>
-serge
> ---
> kernel/capability.c | 338 +++++++++++++++++++++++++++++++++------------------
> 1 files changed, 221 insertions(+), 117 deletions(-)
>
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 901e0fd..0101e84 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -115,11 +115,208 @@ static int cap_validate_magic(cap_user_header_t header, unsigned *tocopy)
> return 0;
> }
>
> +#ifndef CONFIG_SECURITY_FILE_CAPABILITIES
> +
> +/*
> + * Without filesystem capability support, we nominally support one process
> + * setting the capabilities of another
> + */
> +static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
> + kernel_cap_t *pIp, kernel_cap_t *pPp)
> +{
> + struct task_struct *target;
> + int ret;
> +
> + spin_lock(&task_capability_lock);
> + read_lock(&tasklist_lock);
> +
> + if (pid && pid != task_pid_vnr(current)) {
> + target = find_task_by_vpid(pid);
> + if (!target) {
> + ret = -ESRCH;
> + goto out;
> + }
> + } else
> + target = current;
> +
> + ret = security_capget(target, pEp, pIp, pPp);
> +
> +out:
> + read_unlock(&tasklist_lock);
> + spin_unlock(&task_capability_lock);
> +
> + return ret;
> +}
> +
> +/*
> + * cap_set_pg - set capabilities for all processes in a given process
> + * group. We call this holding task_capability_lock and tasklist_lock.
> + */
> +static inline int cap_set_pg(int pgrp_nr, kernel_cap_t *effective,
> + kernel_cap_t *inheritable,
> + kernel_cap_t *permitted)
> +{
> + struct task_struct *g, *target;
> + int ret = -EPERM;
> + int found = 0;
> + struct pid *pgrp;
> +
> + spin_lock(&task_capability_lock);
> + read_lock(&tasklist_lock);
> +
> + pgrp = find_vpid(pgrp_nr);
> + do_each_pid_task(pgrp, PIDTYPE_PGID, g) {
> + target = g;
> + while_each_thread(g, target) {
> + if (!security_capset_check(target, effective,
> + inheritable, permitted)) {
> + security_capset_set(target, effective,
> + inheritable, permitted);
> + ret = 0;
> + }
> + found = 1;
> + }
> + } while_each_pid_task(pgrp, PIDTYPE_PGID, g);
> +
> + read_unlock(&tasklist_lock);
> + spin_unlock(&task_capability_lock);
> +
> + if (!found)
> + ret = 0;
> + return ret;
> +}
> +
> /*
> - * For sys_getproccap() and sys_setproccap(), any of the three
> - * capability set pointers may be NULL -- indicating that that set is
> - * uninteresting and/or not to be changed.
> + * cap_set_all - set capabilities for all processes other than init
> + * and self. We call this holding task_capability_lock and tasklist_lock.
> */
> +static inline int cap_set_all(kernel_cap_t *effective,
> + kernel_cap_t *inheritable,
> + kernel_cap_t *permitted)
> +{
> + struct task_struct *g, *target;
> + int ret = -EPERM;
> + int found = 0;
> +
> + spin_lock(&task_capability_lock);
> + read_lock(&tasklist_lock);
> +
> + do_each_thread(g, target) {
> + if (target == current
> + || is_container_init(target->group_leader))
> + continue;
> + found = 1;
> + if (security_capset_check(target, effective, inheritable,
> + permitted))
> + continue;
> + ret = 0;
> + security_capset_set(target, effective, inheritable, permitted);
> + } while_each_thread(g, target);
> +
> + read_unlock(&tasklist_lock);
> + spin_unlock(&task_capability_lock);
> +
> + if (!found)
> + ret = 0;
> +
> + return ret;
> +}
> +
> +/*
> + * Given the target pid does not refer to the current process we
> + * need more elaborate support... (This support is not present when
> + * filesystem capabilities are configured.)
> + */
> +static inline int do_sys_capset_other_tasks(pid_t pid, kernel_cap_t *effective,
> + kernel_cap_t *inheritable,
> + kernel_cap_t *permitted)
> +{
> + struct task_struct *target;
> + int ret;
> +
> + if (!capable(CAP_SETPCAP))
> + return -EPERM;
> +
> + if (pid == -1) /* all procs other than current and init */
> + return cap_set_all(effective, inheritable, permitted);
> +
> + else if (pid < 0) /* all procs in process group */
> + return cap_set_pg(-pid, effective, inheritable, permitted);
> +
> + /* target != current */
> + spin_lock(&task_capability_lock);
> + read_lock(&tasklist_lock);
> +
> + target = find_task_by_vpid(pid);
> + if (!target)
> + ret = -ESRCH;
> + else {
> + ret = security_capset_check(target, effective, inheritable,
> + permitted);
> +
> + /* having verified that the proposed changes are legal,
> + we now put them into effect. */
> + if (!ret)
> + security_capset_set(target, effective, inheritable,
> + permitted);
> + }
> +
> + read_unlock(&tasklist_lock);
> + spin_unlock(&task_capability_lock);
> +
> + return ret;
> +}
> +
> +#else /* ie., def CONFIG_SECURITY_FILE_CAPABILITIES */
> +
> +/*
> + * If we have configured with filesystem capability support, then the
> + * only thing that can change the capabilities of the current process
> + * is the current process. As such, we can't be in this code at the
> + * same time as we are in the process of setting capabilities in this
> + * process. The net result is that we can limit our use of locks to
> + * when we are reading the caps of another process.
> + */
> +static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
> + kernel_cap_t *pIp, kernel_cap_t *pPp)
> +{
> + int ret;
> +
> + if (pid && (pid != task_pid_vnr(current))) {
> + struct task_struct *target;
> +
> + spin_lock(&task_capability_lock);
> + read_lock(&tasklist_lock);
> +
> + target = find_task_by_vpid(pid);
> + if (!target)
> + ret = -ESRCH;
> + else
> + ret = security_capget(target, pEp, pIp, pPp);
> +
> + read_unlock(&tasklist_lock);
> + spin_unlock(&task_capability_lock);
> + } else
> + ret = security_capget(current, pEp, pIp, pPp);
> +
> + return ret;
> +}
> +
> +/*
> + * With filesystem capability support configured, the kernel does not
> + * permit the changing of capabilities in one process by another
> + * process. (CAP_SETPCAP has much less broad semantics when configured
> + * this way.)
> + */
> +static inline int do_sys_capset_other_tasks(pid_t pid,
> + kernel_cap_t *effective,
> + kernel_cap_t *inheritable,
> + kernel_cap_t *permitted)
> +{
> + return -EPERM;
> +}
> +
> +#endif /* ie., ndef CONFIG_SECURITY_FILE_CAPABILITIES */
>
> /*
> * Atomically modify the effective capabilities returning the original
> @@ -155,7 +352,6 @@ asmlinkage long sys_capget(cap_user_header_t header, cap_user_data_t dataptr)
> {
> int ret = 0;
> pid_t pid;
> - struct task_struct *target;
> unsigned tocopy;
> kernel_cap_t pE, pI, pP;
>
> @@ -169,23 +365,7 @@ asmlinkage long sys_capget(cap_user_header_t header, cap_user_data_t dataptr)
> if (pid < 0)
> return -EINVAL;
>
> - spin_lock(&task_capability_lock);
> - read_lock(&tasklist_lock);
> -
> - if (pid && pid != task_pid_vnr(current)) {
> - target = find_task_by_vpid(pid);
> - if (!target) {
> - ret = -ESRCH;
> - goto out;
> - }
> - } else
> - target = current;
> -
> - ret = security_capget(target, &pE, &pI, &pP);
> -
> -out:
> - read_unlock(&tasklist_lock);
> - spin_unlock(&task_capability_lock);
> + ret = cap_get_target_pid(pid, &pE, &pI, &pP);
>
> if (!ret) {
> struct __user_cap_data_struct kdata[_KERNEL_CAPABILITY_U32S];
> @@ -216,7 +396,6 @@ out:
> * before modification is attempted and the application
> * fails.
> */
> -
> if (copy_to_user(dataptr, kdata, tocopy
> * sizeof(struct __user_cap_data_struct))) {
> return -EFAULT;
> @@ -226,70 +405,8 @@ out:
> return ret;
> }
>
> -/*
> - * cap_set_pg - set capabilities for all processes in a given process
> - * group. We call this holding task_capability_lock and tasklist_lock.
> - */
> -static inline int cap_set_pg(int pgrp_nr, kernel_cap_t *effective,
> - kernel_cap_t *inheritable,
> - kernel_cap_t *permitted)
> -{
> - struct task_struct *g, *target;
> - int ret = -EPERM;
> - int found = 0;
> - struct pid *pgrp;
> -
> - pgrp = find_vpid(pgrp_nr);
> - do_each_pid_task(pgrp, PIDTYPE_PGID, g) {
> - target = g;
> - while_each_thread(g, target) {
> - if (!security_capset_check(target, effective,
> - inheritable,
> - permitted)) {
> - security_capset_set(target, effective,
> - inheritable,
> - permitted);
> - ret = 0;
> - }
> - found = 1;
> - }
> - } while_each_pid_task(pgrp, PIDTYPE_PGID, g);
> -
> - if (!found)
> - ret = 0;
> - return ret;
> -}
> -
> -/*
> - * cap_set_all - set capabilities for all processes other than init
> - * and self. We call this holding task_capability_lock and tasklist_lock.
> - */
> -static inline int cap_set_all(kernel_cap_t *effective,
> - kernel_cap_t *inheritable,
> - kernel_cap_t *permitted)
> -{
> - struct task_struct *g, *target;
> - int ret = -EPERM;
> - int found = 0;
> -
> - do_each_thread(g, target) {
> - if (target == current || is_container_init(target->group_leader))
> - continue;
> - found = 1;
> - if (security_capset_check(target, effective, inheritable,
> - permitted))
> - continue;
> - ret = 0;
> - security_capset_set(target, effective, inheritable, permitted);
> - } while_each_thread(g, target);
> -
> - if (!found)
> - ret = 0;
> - return ret;
> -}
> -
> /**
> - * sys_capset - set capabilities for a process or a group of processes
> + * sys_capset - set capabilities for a process or (*) a group of processes
> * @header: pointer to struct that contains capability version and
> * target pid data
> * @data: pointer to struct that contains the effective, permitted,
> @@ -313,7 +430,6 @@ asmlinkage long sys_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 task_struct *target;
> int ret;
> pid_t pid;
>
> @@ -324,9 +440,6 @@ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
> if (get_user(pid, &header->pid))
> return -EFAULT;
>
> - if (pid && pid != task_pid_vnr(current) && !capable(CAP_SETPCAP))
> - return -EPERM;
> -
> if (copy_from_user(&kdata, data, tocopy
> * sizeof(struct __user_cap_data_struct))) {
> return -EFAULT;
> @@ -344,40 +457,31 @@ asmlinkage long sys_capset(cap_user_header_t header, const cap_user_data_t data)
> i++;
> }
>
> - spin_lock(&task_capability_lock);
> - read_lock(&tasklist_lock);
> -
> - if (pid > 0 && pid != task_pid_vnr(current)) {
> - target = find_task_by_vpid(pid);
> - if (!target) {
> - ret = -ESRCH;
> - goto out;
> - }
> - } else
> - target = current;
> -
> - ret = 0;
> -
> - /* having verified that the proposed changes are legal,
> - we now put them into effect. */
> - if (pid < 0) {
> - if (pid == -1) /* all procs other than current and init */
> - ret = cap_set_all(&effective, &inheritable, &permitted);
> + if (pid && (pid != task_pid_vnr(current)))
> + ret = do_sys_capset_other_tasks(pid, &effective, &inheritable,
> + &permitted);
> + else {
> + /*
> + * This lock is required even when filesystem
> + * capability support is configured - it protects the
> + * sys_capget() call from returning incorrect data in
> + * the case that the targeted process is not the
> + * current one.
> + */
> + spin_lock(&task_capability_lock);
>
> - else /* all procs in process group */
> - ret = cap_set_pg(-pid, &effective, &inheritable,
> - &permitted);
> - } else {
> - ret = security_capset_check(target, &effective, &inheritable,
> + ret = security_capset_check(current, &effective, &inheritable,
> &permitted);
> + /*
> + * Having verified that the proposed changes are
> + * legal, we now put them into effect.
> + */
> if (!ret)
> - security_capset_set(target, &effective, &inheritable,
> + security_capset_set(current, &effective, &inheritable,
> &permitted);
> + spin_unlock(&task_capability_lock);
> }
>
> -out:
> - read_unlock(&tasklist_lock);
> - spin_unlock(&task_capability_lock);
>
> return ret;
> }
> --
> 1.5.3.7
>
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