Re: audit-ptrace patch (untested)

[Alexander Viro <aviro@redhat.com>]

On Tue, Mar 06, 2007 at 09:46:14AM -0500, Stephen Smalley wrote:
> On Mon, 2007-03-05 at 09:50 -0500, Alexander Viro wrote:
> > That one is on top of security_getprocattr() patch.  See bz#228384...
> > 
> <snip>
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index 89875b2..c8465ea 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> <snip>
> > @@ -1874,6 +1887,13 @@ int audit_sockaddr(int len, void *a)
> >  	return 0;
> >  }
> >  
> > +void __audit_ptrace(struct task_struct *t)
> > +{
> > +	struct audit_context *context = current->audit_context;
> > +	context->target_pid = t->pid;
> > +	security_getprocattr(t, "current", &context->obj_ctx);
> > +}
> 
> This will trigger a permission check in selinux_getprocattr, because
> current != t.  So the audit system could be prevented from fetching the
> context in this way based on the current task's permissions.   As with
> the prior patch, I'd suggest using security_task_getsecid() and
> security_secid_to_secctx() [or their selinux-specific equivalents,
> selinux_get_task_sid and selinux_sid_to_string, already in use by audit]
> instead for such internal access to security contexts.

OK...  Here's combined patch (with switch to security_task_getsecid(), etc.)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4f5745a..6bbfe91 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1558,29 +1558,20 @@ static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
 				  size_t count, loff_t *ppos)
 {
 	struct inode * inode = file->f_path.dentry->d_inode;
-	unsigned long page;
+	char *p = NULL;
 	ssize_t length;
 	struct task_struct *task = get_proc_task(inode);
 
-	length = -ESRCH;
 	if (!task)
-		goto out_no_task;
-
-	if (count > PAGE_SIZE)
-		count = PAGE_SIZE;
-	length = -ENOMEM;
-	if (!(page = __get_free_page(GFP_KERNEL)))
-		goto out;
+		return -ESRCH;
 
 	length = security_getprocattr(task,
 				      (char*)file->f_path.dentry->d_name.name,
-				      (void*)page, count);
-	if (length >= 0)
-		length = simple_read_from_buffer(buf, count, ppos, (char *)page, length);
-	free_page(page);
-out:
+				      &p);
 	put_task_struct(task);
-out_no_task:
+	if (length > 0)
+		length = simple_read_from_buffer(buf, count, ppos, p, length);
+	kfree(p);
 	return length;
 }
 
diff --git a/include/linux/audit.h b/include/linux/audit.h
index 229fa01..31b0f40 100644
--- a/include/linux/audit.h
+++ b/include/linux/audit.h
@@ -90,6 +90,7 @@
 #define AUDIT_MQ_GETSETATTR	1315	/* POSIX MQ get/set attribute record type */
 #define AUDIT_KERNEL_OTHER	1316	/* For use by 3rd party modules */
 #define AUDIT_FD_PAIR		1317    /* audit record for pipe/socketpair */
+#define AUDIT_OBJ_PID		1318	/* ptrace target */
 
 #define AUDIT_AVC		1400	/* SE Linux avc denial or grant */
 #define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
@@ -351,6 +352,8 @@ extern void __audit_inode(const char *name, const struct inode *inode);
 extern void __audit_inode_child(const char *dname, const struct inode *inode,
 				const struct inode *parent);
 extern void __audit_inode_update(const struct inode *inode);
+extern void __audit_ptrace(struct task_struct *t);
+
 static inline int audit_dummy_context(void)
 {
 	void *p = current->audit_context;
@@ -376,6 +379,12 @@ static inline void audit_inode_update(const struct inode *inode) {
 		__audit_inode_update(inode);
 }
 
+static inline void audit_ptrace(struct task_struct *t)
+{
+	if (unlikely(!audit_dummy_context()))
+		__audit_ptrace(t);
+}
+
 				/* Private API (for audit.c only) */
 extern unsigned int audit_serial(void);
 extern void auditsc_get_stamp(struct audit_context *ctx,
@@ -476,6 +485,7 @@ extern int audit_n_rules;
 #define audit_mq_timedreceive(d,l,p,t) ({ 0; })
 #define audit_mq_notify(d,n) ({ 0; })
 #define audit_mq_getsetattr(d,s) ({ 0; })
+#define audit_ptrace(t) ((void)0)
 #define audit_n_rules 0
 #endif
 
diff --git a/include/linux/security.h b/include/linux/security.h
index 7f88d97..47e82c1 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -1324,7 +1324,7 @@ struct security_operations {
 
 	void (*d_instantiate) (struct dentry *dentry, struct inode *inode);
 
- 	int (*getprocattr)(struct task_struct *p, char *name, void *value, size_t size);
+ 	int (*getprocattr)(struct task_struct *p, char *name, char **value);
  	int (*setprocattr)(struct task_struct *p, char *name, void *value, size_t size);
 	int (*secid_to_secctx)(u32 secid, char **secdata, u32 *seclen);
 	void (*release_secctx)(char *secdata, u32 seclen);
@@ -2092,9 +2092,9 @@ static inline void security_d_instantiate (struct dentry *dentry, struct inode *
 	security_ops->d_instantiate (dentry, inode);
 }
 
-static inline int security_getprocattr(struct task_struct *p, char *name, void *value, size_t size)
+static inline int security_getprocattr(struct task_struct *p, char *name, char **value)
 {
-	return security_ops->getprocattr(p, name, value, size);
+	return security_ops->getprocattr(p, name, value);
 }
 
 static inline int security_setprocattr(struct task_struct *p, char *name, void *value, size_t size)
@@ -2749,7 +2749,7 @@ static inline int security_sem_semop (struct sem_array * sma,
 static inline void security_d_instantiate (struct dentry *dentry, struct inode *inode)
 { }
 
-static inline int security_getprocattr(struct task_struct *p, char *name, void *value, size_t size)
+static inline int security_getprocattr(struct task_struct *p, char *name, char **value)
 {
 	return -EINVAL;
 }
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 3599558..f8875cb 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -209,6 +209,9 @@ struct audit_context {
 	unsigned long	    personality;
 	int		    arch;
 
+	pid_t		    target_pid;
+	char *		    obj_ctx;
+
 #if AUDIT_DEBUG
 	int		    put_count;
 	int		    ino_count;
@@ -729,6 +732,7 @@ static inline void audit_free_context(struct audit_context *context)
 		audit_free_names(context);
 		audit_free_aux(context);
 		kfree(context->filterkey);
+		kfree(context->obj_ctx);
 		kfree(context);
 		context  = previous;
 	} while (context);
@@ -739,28 +743,26 @@ static inline void audit_free_context(struct audit_context *context)
 void audit_log_task_context(struct audit_buffer *ab)
 {
 	char *ctx = NULL;
-	ssize_t len = 0;
+	unsigned len;
+	int error;
+	u32 sid;
 
-	len = security_getprocattr(current, "current", NULL, 0);
-	if (len < 0) {
-		if (len != -EINVAL)
+	security_task_getsecid(current, &sid);
+	if (!sid)
+		return;
+
+	error = security_secid_to_secctx(sid, &ctx, &len);
+	if (error) {
+		if (error != -EINVAL)
 			goto error_path;
 		return;
 	}
 
-	ctx = kmalloc(len, GFP_KERNEL);
-	if (!ctx)
-		goto error_path;
-
-	len = security_getprocattr(current, "current", ctx, len);
-	if (len < 0 )
-		goto error_path;
-
 	audit_log_format(ab, " subj=%s", ctx);
+	kfree(ctx);
 	return;
 
 error_path:
-	kfree(ctx);
 	audit_panic("error in audit_log_task_context");
 	return;
 }
@@ -975,6 +977,16 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 		audit_log_end(ab);
 	}
 
+	if (context->target_pid) {
+		char *s = context->obj_ctx ? context->obj_ctx : "(none)";
+		ab =audit_log_start(context, GFP_KERNEL, AUDIT_OBJ_PID);
+		if (ab) {
+			audit_log_format(ab, "opid=%d obj=%s",
+					 context->target_pid, s);
+			audit_log_end(ab);
+		}
+	}
+
 	if (context->pwd && context->pwdmnt) {
 		ab = audit_log_start(context, GFP_KERNEL, AUDIT_CWD);
 		if (ab) {
@@ -1195,6 +1207,9 @@ void audit_syscall_exit(int valid, long return_code)
 	} else {
 		audit_free_names(context);
 		audit_free_aux(context);
+		kfree(context->obj_ctx);
+		context->obj_ctx = NULL;
+		context->target_pid = 0;
 		kfree(context->filterkey);
 		context->filterkey = NULL;
 		tsk->audit_context = context;
@@ -1882,6 +1897,19 @@ int audit_sockaddr(int len, void *a)
 	return 0;
 }
 
+void __audit_ptrace(struct task_struct *t)
+{
+	struct audit_context *context = current->audit_context;
+	unsigned len;
+	u32 sid;
+
+	context->target_pid = t->pid;
+
+	security_task_getsecid(t, &sid);
+	if (sid)
+		security_secid_to_secctx(sid, &context->obj_ctx, &len);
+}
+
 /**
  * audit_avc_path - record the granting or denial of permissions
  * @dentry: dentry to record
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 4d50e06..ad7949a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -18,6 +18,7 @@
 #include <linux/ptrace.h>
 #include <linux/security.h>
 #include <linux/signal.h>
+#include <linux/audit.h>
 
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
@@ -161,6 +162,8 @@ int ptrace_attach(struct task_struct *task)
 {
 	int retval;
 
+	audit_ptrace(task);
+
 	retval = -EPERM;
 	if (task->pid <= 1)
 		goto out;
diff --git a/security/dummy.c b/security/dummy.c
index 558795b..8ffd764 100644
--- a/security/dummy.c
+++ b/security/dummy.c
@@ -907,7 +907,7 @@ static void dummy_d_instantiate (struct dentry *dentry, struct inode *inode)
 	return;
 }
 
-static int dummy_getprocattr(struct task_struct *p, char *name, void *value, size_t size)
+static int dummy_getprocattr(struct task_struct *p, char *name, char **value)
 {
 	return -EINVAL;
 }
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index b1ac22d..0b265a5 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4468,11 +4468,12 @@ static void selinux_d_instantiate (struct dentry *dentry, struct inode *inode)
 }
 
 static int selinux_getprocattr(struct task_struct *p,
-			       char *name, void *value, size_t size)
+			       char *name, char **value)
 {
 	struct task_security_struct *tsec;
 	u32 sid;
 	int error;
+	unsigned len;
 
 	if (current != p) {
 		error = task_has_perm(current, p, PROCESS__GETATTR);
@@ -4500,7 +4501,10 @@ static int selinux_getprocattr(struct task_struct *p,
 	if (!sid)
 		return 0;
 
-	return selinux_getsecurity(sid, value, size);
+	error = security_sid_to_context(sid, value, &len);
+	if (error)
+		return error;
+	return len;
 }
 
 static int selinux_setprocattr(struct task_struct *p,