[Devel] Re: [PATCH 2/2] hijack: update task_alloc_security

Rodrigo Rubira Branco (BSDaemon) rodrigo at kernelhacking.com
Tue Nov 27 03:08:31 PST 2007


It will give another easy way to locate selinux security structures inside
the kernel, will not?

Again, if you have a kernel vulnerability and this feature, someone will
easily disable selinux for the process, or just change the security concerns
for it ;).


cya,


Rodrigo (BSDaemon).

--
http://www.kernelhacking.com/rodrigo

Kernel Hacking: If i really know, i can hack

GPG KeyID: 1FCEDEA1


--------- Mensagem Original --------
De: Joshua Brindle <method at manicmethod.com>
Para: Mark Nelson <markn at au1.ibm.com>
Cópia: containers at lists.linux-foundation.org,
linux-security-module at vger.kernel.org, selinux at tycho.nsa.gov,
menage at google.com, Stephen Smalley <sds at tycho.nsa.gov>, James Morris
<jmorris at namei.org>, Serge E. Hallyn <serue at us.ibm.com>
Assunto: Re: [PATCH 2/2] hijack: update task_alloc_security
Data: 27/11/07 02:38

>
> Mark Nelson wrote:
> &gt; Subject: [PATCH 2/2] hijack: update task_alloc_security
> &gt;
> &gt; Update task_alloc_security() to take the hijacked task as a second
> &gt; argument.
> &gt;
> &gt; For the selinux version, refuse permission if hijack_src!=current,
> &gt; since we have no idea what the proper behavior is.  Even if we
> &gt; assume that the resulting child should be in the hijacked task's
> &gt; domain, depending on the policy that may not be enough information
> &gt; since init_t executing /bin/bash could result in a different domain
> &gt; than login_t executing /bin/bash.
> &gt;
> &gt;
> This means its basically not possible to hijack tasks with SELinux
> right? It would be a shame if this weren't useful to people running
SELinux.
>
> It seems to me (I may be wrong, I'm sure someone will let me know if I
> am) that the right way to handle this with SELinux is to check to see if
> the current task (caller of sys_hijack) has permission to ptrace (or
> some other permission deemed suitable, perhaps a new one) and if so copy
> the security blob pointer from the hijacked task to the new one (we
> don't want tranquility problems).
>
>  From your paragraph above it seems like you were thinking there should
> be a transition at hijack time but we don't automatically transition
> anywhere except exec.
>
> Anyway, I just don't think you should completely disable this for
> SELinux users.
>
> &gt; Signed-off-by: Serge Hallyn &lt;serue at us.ibm.com&gt;
> &gt; Signed-off-by: Mark Nelson &lt;markn at au1.ibm.com&gt;
> &gt; ---
> &gt;  include/linux/security.h |   12 +++++++++---
> &gt;  kernel/fork.c            |    2 +-
> &gt;  security/dummy.c         |    3 ++-
> &gt;  security/security.c      |    4 ++--
> &gt;  security/selinux/hooks.c |    6 +++++-
> &gt;  5 files changed, 19 insertions(+), 8 deletions(-)
> &gt;
> &gt; Index: upstream/include/linux/security.h
> &gt; ===================================================================
> &gt; --- upstream.orig/include/linux/security.h
> &gt; +++ upstream/include/linux/security.h
> &gt; @@ -545,9 +545,13 @@ struct request_sock;
> &gt;   *	Return 0 if permission is granted.
> &gt;   * @task_alloc_security:
> &gt;   *	@p contains the task_struct for child process.
> &gt; + *	@task contains the task_struct for process to be hijacked
> &gt;   *	Allocate and attach a security structure to the p-&gt;security
field. The
> &gt;   *	security field is initialized to NULL when the task structure is
> &gt;   *	allocated.
> &gt; + *	@task will usually be current.  If it is not equal to current,
then
> &gt; + *	a sys_hijack system call is going on, and current is asking for a
> &gt; + *	child to be created in the context of the hijack src, @task.
> &gt;   *	Return 0 if operation was successful.
> &gt;   * @task_free_security:
> &gt;   *	@p contains the task_struct for process.
> &gt; @@ -1301,7 +1305,8 @@ struct security_operations {
> &gt;  	int (*dentry_open)  (struct file *file);
> &gt;
> &gt;  	int (*task_create) (unsigned long clone_flags);
> &gt; -	int (*task_alloc_security) (struct task_struct * p);
> &gt; +	int (*task_alloc_security) (struct task_struct *p,
> &gt; +				    struct task_struct *task);
> &gt;  	void (*task_free_security) (struct task_struct * p);
> &gt;  	int (*task_setuid) (uid_t id0, uid_t id1, uid_t id2, int flags);
> &gt;  	int (*task_post_setuid) (uid_t old_ruid /* or fsuid */ ,
> &gt; @@ -1549,7 +1554,7 @@ int security_file_send_sigiotask(struct
> &gt;  int security_file_receive(struct file *file);
> &gt;  int security_dentry_open(struct file *file);
> &gt;  int security_task_create(unsigned long clone_flags);
> &gt; -int security_task_alloc(struct task_struct *p);
> &gt; +int security_task_alloc(struct task_struct *p, struct task_struct
*task);
> &gt;  void security_task_free(struct task_struct *p);
> &gt;  int security_task_setuid(uid_t id0, uid_t id1, uid_t id2, int
flags);
> &gt;  int security_task_post_setuid(uid_t old_ruid, uid_t old_euid,
> &gt; @@ -2021,7 +2026,8 @@ static inline int security_task_create (
> &gt;  	return 0;
> &gt;  }
> &gt;
> &gt; -static inline int security_task_alloc (struct task_struct *p)
> &gt; +static inline int security_task_alloc(struct task_struct *p,
> &gt; +				       struct task_struct *task)
> &gt;  {
> &gt;  	return 0;
> &gt;  }
> &gt; Index: upstream/kernel/fork.c
> &gt; ===================================================================
> &gt; --- upstream.orig/kernel/fork.c
> &gt; +++ upstream/kernel/fork.c
> &gt; @@ -1177,7 +1177,7 @@ static struct task_struct *copy_process(
> &gt;  	/* Perform scheduler related setup. Assign this task to a CPU. */
> &gt;  	sched_fork(p, clone_flags);
> &gt;
> &gt; -	if ((retval = security_task_alloc(p)))
> &gt; +	if ((retval = security_task_alloc(p, task)))
> &gt;  		goto bad_fork_cleanup_policy;
> &gt;  	if ((retval = audit_alloc(p)))
> &gt;  		goto bad_fork_cleanup_security;
> &gt; Index: upstream/security/dummy.c
> &gt; ===================================================================
> &gt; --- upstream.orig/security/dummy.c
> &gt; +++ upstream/security/dummy.c
> &gt; @@ -475,7 +475,8 @@ static int dummy_task_create (unsigned l
> &gt;  	return 0;
> &gt;  }
> &gt;
> &gt; -static int dummy_task_alloc_security (struct task_struct *p)
> &gt; +static int dummy_task_alloc_security(struct task_struct *p,
> &gt; +				      struct task_struct *task)
> &gt;  {
> &gt;  	return 0;
> &gt;  }
> &gt; Index: upstream/security/security.c
> &gt; ===================================================================
> &gt; --- upstream.orig/security/security.c
> &gt; +++ upstream/security/security.c
> &gt; @@ -568,9 +568,9 @@ int security_task_create(unsigned long c
> &gt;  	return security_ops-&gt;task_create(clone_flags);
> &gt;  }
> &gt;
> &gt; -int security_task_alloc(struct task_struct *p)
> &gt; +int security_task_alloc(struct task_struct *p, struct task_struct
*task)
> &gt;  {
> &gt; -	return security_ops-&gt;task_alloc_security(p);
> &gt; +	return security_ops-&gt;task_alloc_security(p, task);
> &gt;  }
> &gt;
> &gt;  void security_task_free(struct task_struct *p)
> &gt; Index: upstream/security/selinux/hooks.c
> &gt; ===================================================================
> &gt; --- upstream.orig/security/selinux/hooks.c
> &gt; +++ upstream/security/selinux/hooks.c
> &gt; @@ -2788,11 +2788,15 @@ static int selinux_task_create(unsigned
> &gt;  	return task_has_perm(current, current, PROCESS__FORK);
> &gt;  }
> &gt;
> &gt; -static int selinux_task_alloc_security(struct task_struct *tsk)
> &gt; +static int selinux_task_alloc_security(struct task_struct *tsk,
> &gt; +				      struct task_struct *hijack_src)
> &gt;  {
> &gt;  	struct task_security_struct *tsec1, *tsec2;
> &gt;  	int rc;
> &gt;
> &gt; +	if (hijack_src != current)
> &gt; +		return -EPERM;
> &gt; +
> &gt;  	tsec1 = current-&gt;security;
> &gt;
> &gt;  	rc = task_alloc_security(tsk);
> &gt; -
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