CRED: Add some configurable debugging [try #6]
Add a config option (CONFIG_DEBUG_CREDENTIALS) to turn on some debug checking
for credential management. The additional code keeps track of the number of
pointers from task_structs to any given cred struct, and checks to see that
this number never exceeds the usage count of the cred struct (which includes
all references, not just those from task_structs).
Furthermore, if SELinux is enabled, the code also checks that the security
pointer in the cred struct is never seen to be invalid.
This attempts to catch the bug whereby inode_has_perm() faults in an nfsd
kernel thread on seeing cred->security be a NULL pointer (it appears that the
credential struct has been previously released):
http://www.kerneloops.org/oops.php?number=252883
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/kernel/cred.c b/kernel/cred.c
index 1bb4d7e..24dd2f5 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -18,6 +18,18 @@
#include <linux/cn_proc.h>
#include "cred-internals.h"
+#if 0
+#define kdebug(FMT, ...) \
+ printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
+#else
+static inline __attribute__((format(printf, 1, 2)))
+void no_printk(const char *fmt, ...)
+{
+}
+#define kdebug(FMT, ...) \
+ no_printk("[%-5.5s%5u] "FMT"\n", current->comm, current->pid ,##__VA_ARGS__)
+#endif
+
static struct kmem_cache *cred_jar;
/*
@@ -36,6 +48,10 @@
*/
struct cred init_cred = {
.usage = ATOMIC_INIT(4),
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ .subscribers = ATOMIC_INIT(2),
+ .magic = CRED_MAGIC,
+#endif
.securebits = SECUREBITS_DEFAULT,
.cap_inheritable = CAP_INIT_INH_SET,
.cap_permitted = CAP_FULL_SET,
@@ -48,6 +64,31 @@
#endif
};
+static inline void set_cred_subscribers(struct cred *cred, int n)
+{
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ atomic_set(&cred->subscribers, n);
+#endif
+}
+
+static inline int read_cred_subscribers(const struct cred *cred)
+{
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ return atomic_read(&cred->subscribers);
+#else
+ return 0;
+#endif
+}
+
+static inline void alter_cred_subscribers(const struct cred *_cred, int n)
+{
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ struct cred *cred = (struct cred *) _cred;
+
+ atomic_add(n, &cred->subscribers);
+#endif
+}
+
/*
* Dispose of the shared task group credentials
*/
@@ -85,9 +126,22 @@
{
struct cred *cred = container_of(rcu, struct cred, rcu);
+ kdebug("put_cred_rcu(%p)", cred);
+
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ if (cred->magic != CRED_MAGIC_DEAD ||
+ atomic_read(&cred->usage) != 0 ||
+ read_cred_subscribers(cred) != 0)
+ panic("CRED: put_cred_rcu() sees %p with"
+ " mag %x, put %p, usage %d, subscr %d\n",
+ cred, cred->magic, cred->put_addr,
+ atomic_read(&cred->usage),
+ read_cred_subscribers(cred));
+#else
if (atomic_read(&cred->usage) != 0)
panic("CRED: put_cred_rcu() sees %p with usage %d\n",
cred, atomic_read(&cred->usage));
+#endif
security_cred_free(cred);
key_put(cred->thread_keyring);
@@ -106,12 +160,47 @@
*/
void __put_cred(struct cred *cred)
{
+ kdebug("__put_cred(%p{%d,%d})", cred,
+ atomic_read(&cred->usage),
+ read_cred_subscribers(cred));
+
BUG_ON(atomic_read(&cred->usage) != 0);
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ BUG_ON(read_cred_subscribers(cred) != 0);
+ cred->magic = CRED_MAGIC_DEAD;
+ cred->put_addr = __builtin_return_address(0);
+#endif
+ BUG_ON(cred == current->cred);
+ BUG_ON(cred == current->real_cred);
call_rcu(&cred->rcu, put_cred_rcu);
}
EXPORT_SYMBOL(__put_cred);
+/*
+ * Clean up a task's credentials when it exits
+ */
+void exit_creds(struct task_struct *tsk)
+{
+ struct cred *cred;
+
+ kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
+ atomic_read(&tsk->cred->usage),
+ read_cred_subscribers(tsk->cred));
+
+ cred = (struct cred *) tsk->real_cred;
+ tsk->real_cred = NULL;
+ validate_creds(cred);
+ alter_cred_subscribers(cred, -1);
+ put_cred(cred);
+
+ cred = (struct cred *) tsk->cred;
+ tsk->cred = NULL;
+ validate_creds(cred);
+ alter_cred_subscribers(cred, -1);
+ put_cred(cred);
+}
+
/**
* prepare_creds - Prepare a new set of credentials for modification
*
@@ -132,16 +221,19 @@
const struct cred *old;
struct cred *new;
- BUG_ON(atomic_read(&task->real_cred->usage) < 1);
+ validate_process_creds();
new = kmem_cache_alloc(cred_jar, GFP_KERNEL);
if (!new)
return NULL;
+ kdebug("prepare_creds() alloc %p", new);
+
old = task->cred;
memcpy(new, old, sizeof(struct cred));
atomic_set(&new->usage, 1);
+ set_cred_subscribers(new, 0);
get_group_info(new->group_info);
get_uid(new->user);
@@ -157,6 +249,7 @@
if (security_prepare_creds(new, old, GFP_KERNEL) < 0)
goto error;
+ validate_creds(new);
return new;
error:
@@ -229,9 +322,12 @@
if (!new)
return NULL;
+ kdebug("prepare_usermodehelper_creds() alloc %p", new);
+
memcpy(new, &init_cred, sizeof(struct cred));
atomic_set(&new->usage, 1);
+ set_cred_subscribers(new, 0);
get_group_info(new->group_info);
get_uid(new->user);
@@ -250,6 +346,7 @@
#endif
if (security_prepare_creds(new, &init_cred, GFP_ATOMIC) < 0)
goto error;
+ validate_creds(new);
BUG_ON(atomic_read(&new->usage) != 1);
return new;
@@ -286,6 +383,10 @@
) {
p->real_cred = get_cred(p->cred);
get_cred(p->cred);
+ alter_cred_subscribers(p->cred, 2);
+ kdebug("share_creds(%p{%d,%d})",
+ p->cred, atomic_read(&p->cred->usage),
+ read_cred_subscribers(p->cred));
atomic_inc(&p->cred->user->processes);
return 0;
}
@@ -331,6 +432,8 @@
atomic_inc(&new->user->processes);
p->cred = p->real_cred = get_cred(new);
+ alter_cred_subscribers(new, 2);
+ validate_creds(new);
return 0;
error_put:
@@ -355,13 +458,20 @@
int commit_creds(struct cred *new)
{
struct task_struct *task = current;
- const struct cred *old;
+ const struct cred *old = task->real_cred;
- BUG_ON(task->cred != task->real_cred);
- BUG_ON(atomic_read(&task->real_cred->usage) < 2);
+ kdebug("commit_creds(%p{%d,%d})", new,
+ atomic_read(&new->usage),
+ read_cred_subscribers(new));
+
+ BUG_ON(task->cred != old);
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ BUG_ON(read_cred_subscribers(old) < 2);
+ validate_creds(old);
+ validate_creds(new);
+#endif
BUG_ON(atomic_read(&new->usage) < 1);
- old = task->real_cred;
security_commit_creds(new, old);
get_cred(new); /* we will require a ref for the subj creds too */
@@ -390,12 +500,14 @@
* cheaply with the new uid cache, so if it matters
* we should be checking for it. -DaveM
*/
+ alter_cred_subscribers(new, 2);
if (new->user != old->user)
atomic_inc(&new->user->processes);
rcu_assign_pointer(task->real_cred, new);
rcu_assign_pointer(task->cred, new);
if (new->user != old->user)
atomic_dec(&old->user->processes);
+ alter_cred_subscribers(old, -2);
sched_switch_user(task);
@@ -428,6 +540,13 @@
*/
void abort_creds(struct cred *new)
{
+ kdebug("abort_creds(%p{%d,%d})", new,
+ atomic_read(&new->usage),
+ read_cred_subscribers(new));
+
+#ifdef CONFIG_DEBUG_CREDENTIALS
+ BUG_ON(read_cred_subscribers(new) != 0);
+#endif
BUG_ON(atomic_read(&new->usage) < 1);
put_cred(new);
}
@@ -444,7 +563,20 @@
{
const struct cred *old = current->cred;
- rcu_assign_pointer(current->cred, get_cred(new));
+ kdebug("override_creds(%p{%d,%d})", new,
+ atomic_read(&new->usage),
+ read_cred_subscribers(new));
+
+ validate_creds(old);
+ validate_creds(new);
+ get_cred(new);
+ alter_cred_subscribers(new, 1);
+ rcu_assign_pointer(current->cred, new);
+ alter_cred_subscribers(old, -1);
+
+ kdebug("override_creds() = %p{%d,%d}", old,
+ atomic_read(&old->usage),
+ read_cred_subscribers(old));
return old;
}
EXPORT_SYMBOL(override_creds);
@@ -460,7 +592,15 @@
{
const struct cred *override = current->cred;
+ kdebug("revert_creds(%p{%d,%d})", old,
+ atomic_read(&old->usage),
+ read_cred_subscribers(old));
+
+ validate_creds(old);
+ validate_creds(override);
+ alter_cred_subscribers(old, 1);
rcu_assign_pointer(current->cred, old);
+ alter_cred_subscribers(override, -1);
put_cred(override);
}
EXPORT_SYMBOL(revert_creds);
@@ -502,11 +642,15 @@
if (!new)
return NULL;
+ kdebug("prepare_kernel_cred() alloc %p", new);
+
if (daemon)
old = get_task_cred(daemon);
else
old = get_cred(&init_cred);
+ validate_creds(old);
+
*new = *old;
get_uid(new->user);
get_group_info(new->group_info);
@@ -526,7 +670,9 @@
goto error;
atomic_set(&new->usage, 1);
+ set_cred_subscribers(new, 0);
put_cred(old);
+ validate_creds(new);
return new;
error:
@@ -589,3 +735,95 @@
return security_kernel_create_files_as(new, inode);
}
EXPORT_SYMBOL(set_create_files_as);
+
+#ifdef CONFIG_DEBUG_CREDENTIALS
+
+/*
+ * dump invalid credentials
+ */
+static void dump_invalid_creds(const struct cred *cred, const char *label,
+ const struct task_struct *tsk)
+{
+ printk(KERN_ERR "CRED: %s credentials: %p %s%s%s\n",
+ label, cred,
+ cred == &init_cred ? "[init]" : "",
+ cred == tsk->real_cred ? "[real]" : "",
+ cred == tsk->cred ? "[eff]" : "");
+ printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
+ cred->magic, cred->put_addr);
+ printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
+ atomic_read(&cred->usage),
+ read_cred_subscribers(cred));
+ printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
+ cred->uid, cred->euid, cred->suid, cred->fsuid);
+ printk(KERN_ERR "CRED: ->*gid = { %d,%d,%d,%d }\n",
+ cred->gid, cred->egid, cred->sgid, cred->fsgid);
+#ifdef CONFIG_SECURITY
+ printk(KERN_ERR "CRED: ->security is %p\n", cred->security);
+ if ((unsigned long) cred->security >= PAGE_SIZE &&
+ (((unsigned long) cred->security & 0xffffff00) !=
+ (POISON_FREE << 24 | POISON_FREE << 16 | POISON_FREE << 8)))
+ printk(KERN_ERR "CRED: ->security {%x, %x}\n",
+ ((u32*)cred->security)[0],
+ ((u32*)cred->security)[1]);
+#endif
+}
+
+/*
+ * report use of invalid credentials
+ */
+void __invalid_creds(const struct cred *cred, const char *file, unsigned line)
+{
+ printk(KERN_ERR "CRED: Invalid credentials\n");
+ printk(KERN_ERR "CRED: At %s:%u\n", file, line);
+ dump_invalid_creds(cred, "Specified", current);
+ BUG();
+}
+EXPORT_SYMBOL(__invalid_creds);
+
+/*
+ * check the credentials on a process
+ */
+void __validate_process_creds(struct task_struct *tsk,
+ const char *file, unsigned line)
+{
+ if (tsk->cred == tsk->real_cred) {
+ if (unlikely(read_cred_subscribers(tsk->cred) < 2 ||
+ creds_are_invalid(tsk->cred)))
+ goto invalid_creds;
+ } else {
+ if (unlikely(read_cred_subscribers(tsk->real_cred) < 1 ||
+ read_cred_subscribers(tsk->cred) < 1 ||
+ creds_are_invalid(tsk->real_cred) ||
+ creds_are_invalid(tsk->cred)))
+ goto invalid_creds;
+ }
+ return;
+
+invalid_creds:
+ printk(KERN_ERR "CRED: Invalid process credentials\n");
+ printk(KERN_ERR "CRED: At %s:%u\n", file, line);
+
+ dump_invalid_creds(tsk->real_cred, "Real", tsk);
+ if (tsk->cred != tsk->real_cred)
+ dump_invalid_creds(tsk->cred, "Effective", tsk);
+ else
+ printk(KERN_ERR "CRED: Effective creds == Real creds\n");
+ BUG();
+}
+EXPORT_SYMBOL(__validate_process_creds);
+
+/*
+ * check creds for do_exit()
+ */
+void validate_creds_for_do_exit(struct task_struct *tsk)
+{
+ kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
+ tsk->real_cred, tsk->cred,
+ atomic_read(&tsk->cred->usage),
+ read_cred_subscribers(tsk->cred));
+
+ __validate_process_creds(tsk, __FILE__, __LINE__);
+}
+
+#endif /* CONFIG_DEBUG_CREDENTIALS */