Re: 2.6.12-rc4-mm2 - sleeping function called from invalid context at mm/slab.c:2502

[Stephen Smalley <sds@tycho.nsa.gov>]

On Fri, 2005-05-20 at 16:36 +0100, David Woodhouse wrote:
> On Fri, 2005-05-20 at 11:09 -0400, Stephen Smalley wrote:
> > The lock is being held by the af_unix code (unix_state_wlock), not
> > avc_audit; the AVC is called under all kinds of circumstances (softirq,
> > hard irq, caller holding locks on relevant objects) for permission
> > checking and must never sleep.
> > 
> > One option might be to defer some of the AVC auditing to the audit
> > framework (e.g. save the vfsmount and dentry on the current audit
> > context and let audit_log_exit perform the audit_log_d_path).
> 
> Yeah, maybe. Assuming you pin them, it's easy enough to hang something
> off the audit context's aux list which refers to them. I'm really not
> that fond of the idea of allocating a whole PATH_MAX with GFP_ATOMIC.

Untested patch below, relative to 2.6.12-rc4-mm2 plus your socketcall
patch to avoid the obvious conflict there.  Is this what you had in
mind?

 include/linux/audit.h  |    2 ++
 kernel/auditsc.c       |   38 ++++++++++++++++++++++++++++++++++++++
 security/selinux/avc.c |   17 ++++++++---------
 3 files changed, 48 insertions(+), 9 deletions(-)

--- linux-2.6.12-rc4-mm2/include/linux/audit.h.orig	2005-05-20 12:37:41.000000000 -0400
+++ linux-2.6.12-rc4-mm2/include/linux/audit.h	2005-05-20 12:38:15.000000000 -0400
@@ -238,6 +238,7 @@ extern uid_t audit_get_loginuid(struct a
 extern int audit_ipc_perms(unsigned long qbytes, uid_t uid, gid_t gid, mode_t mode);
 extern int audit_socketcall(int nargs, unsigned long *args);
 extern int audit_sockaddr(int len, void *addr);
+extern int audit_avc_path(struct dentry *dentry, struct vfsmount *mnt);
 extern void audit_signal_info(int sig, struct task_struct *t);
 #else
 #define audit_alloc(t) ({ 0; })
@@ -253,6 +254,7 @@ extern void audit_signal_info(int sig, s
 #define audit_ipc_perms(q,u,g,m) ({ 0; })
 #define audit_socketcall(n,a) ({ 0; })
 #define audit_sockaddr(len, addr) ({ 0; })
+#define audit_avc_path(dentry, mnt) ({ 0; })
 #define audit_signal_info(s,t) do { ; } while (0)
 #endif
 
--- linux-2.6.12-rc4-mm2/kernel/auditsc.c.orig	2005-05-20 12:37:19.000000000 -0400
+++ linux-2.6.12-rc4-mm2/kernel/auditsc.c	2005-05-20 12:43:05.000000000 -0400
@@ -34,6 +34,7 @@
 #include <asm/types.h>
 #include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/mount.h>
 #include <linux/socket.h>
 #include <linux/audit.h>
 #include <linux/personality.h>
@@ -124,6 +125,11 @@ struct audit_aux_data_sockaddr {
 	char			a[0];
 };
 
+struct audit_aux_data_avc {
+	struct audit_aux_data	d;
+	struct dentry		*dentry;
+	struct vfsmount		*mnt;
+};
 
 /* The per-task audit context. */
 struct audit_context {
@@ -553,6 +559,11 @@ static inline void audit_free_aux(struct
 	struct audit_aux_data *aux;
 
 	while ((aux = context->aux)) {
+		if (aux->type == AUDIT_AVC) {
+			struct audit_aux_data_avc *axi = (void *)aux;
+			dput(axi->dentry);
+			mntput(axi->mnt);
+		}
 		context->aux = aux->next;
 		kfree(aux);
 	}
@@ -728,6 +739,12 @@ static void audit_log_exit(struct audit_
 			} /* case AUDIT_SOCKADDR */
 			break;
 
+		case AUDIT_AVC: {
+			struct audit_aux_data_avc *axi = (void *)aux;
+			if (axi->dentry)
+				audit_log_d_path(ab, "path=", axi->dentry, axi->mnt);
+			} /* case AUDIT_AVC */
+			break;
 		}
 		audit_log_end(ab);
 
@@ -1128,6 +1145,27 @@ int audit_sockaddr(int len, void *a)
 	return 0;
 }
 
+int audit_avc_path(struct dentry *dentry, struct vfsmount *mnt)
+{
+	struct audit_aux_data_avc *ax;
+	struct audit_context *context = current->audit_context;
+
+	if (likely(!context))
+		return 0;
+
+	ax = kmalloc(sizeof(*ax), GFP_ATOMIC);
+	if (!ax)
+		return -ENOMEM;
+
+	ax->dentry = dget(dentry);
+	ax->mnt = mntget(mnt);
+
+	ax->d.type = AUDIT_AVC;
+	ax->d.next = context->aux;
+	context->aux = (void *)ax;
+	return 0;
+}
+
 void audit_signal_info(int sig, struct task_struct *t)
 {
 	extern pid_t audit_sig_pid;
--- linux-2.6.12-rc4-mm2/security/selinux/avc.c.orig	2005-05-20 12:37:41.000000000 -0400
+++ linux-2.6.12-rc4-mm2/security/selinux/avc.c	2005-05-20 12:39:06.000000000 -0400
@@ -566,13 +566,10 @@ void avc_audit(u32 ssid, u32 tsid,
 		case AVC_AUDIT_DATA_FS:
 			if (a->u.fs.dentry) {
 				struct dentry *dentry = a->u.fs.dentry;
-				if (a->u.fs.mnt) {
-					audit_log_d_path(ab, "path=", dentry,
-							a->u.fs.mnt);
-				} else {
-					audit_log_format(ab, " name=%s",
-							 dentry->d_name.name);
-				}
+				if (a->u.fs.mnt)
+					audit_avc_path(dentry, a->u.fs.mnt);
+				audit_log_format(ab, " name=%s",
+						 dentry->d_name.name);
 				inode = dentry->d_inode;
 			} else if (a->u.fs.inode) {
 				struct dentry *dentry;
@@ -623,8 +620,10 @@ void avc_audit(u32 ssid, u32 tsid,
 				case AF_UNIX:
 					u = unix_sk(sk);
 					if (u->dentry) {
-						audit_log_d_path(ab, "path=",
-							u->dentry, u->mnt);
+						audit_avc_path(u->dentry, u->mnt);
+						audit_log_format(ab, " name=%s",
+								 u->dentry->d_name.name);
+
 						break;
 					}
 					if (!u->addr)


-- 
Stephen Smalley
National Security Agency

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