[PATCH] Fix sysctl unregistration oops (CVE-2005-2709)
You could open the /proc/sys/net/ipv4/conf/<if>/<whatever> file, then
wait for interface to go away, try to grab as much memory as possible in
hope to hit the (kfreed) ctl_table. Then fill it with pointers to your
function. Then do read from file you've opened and if you are lucky,
you'll get it called as ->proc_handler() in kernel mode.
So this is at least an Oops and possibly more. It does depend on an
interface going away though, so less of a security risk than it would
otherwise be.
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index c4f35f9..9990e10 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -169,7 +169,7 @@
extern struct proc_dir_entry *proc_sys_root;
-static void register_proc_table(ctl_table *, struct proc_dir_entry *);
+static void register_proc_table(ctl_table *, struct proc_dir_entry *, void *);
static void unregister_proc_table(ctl_table *, struct proc_dir_entry *);
#endif
@@ -992,10 +992,51 @@
extern void init_irq_proc (void);
+static DEFINE_SPINLOCK(sysctl_lock);
+
+/* called under sysctl_lock */
+static int use_table(struct ctl_table_header *p)
+{
+ if (unlikely(p->unregistering))
+ return 0;
+ p->used++;
+ return 1;
+}
+
+/* called under sysctl_lock */
+static void unuse_table(struct ctl_table_header *p)
+{
+ if (!--p->used)
+ if (unlikely(p->unregistering))
+ complete(p->unregistering);
+}
+
+/* called under sysctl_lock, will reacquire if has to wait */
+static void start_unregistering(struct ctl_table_header *p)
+{
+ /*
+ * if p->used is 0, nobody will ever touch that entry again;
+ * we'll eliminate all paths to it before dropping sysctl_lock
+ */
+ if (unlikely(p->used)) {
+ struct completion wait;
+ init_completion(&wait);
+ p->unregistering = &wait;
+ spin_unlock(&sysctl_lock);
+ wait_for_completion(&wait);
+ spin_lock(&sysctl_lock);
+ }
+ /*
+ * do not remove from the list until nobody holds it; walking the
+ * list in do_sysctl() relies on that.
+ */
+ list_del_init(&p->ctl_entry);
+}
+
void __init sysctl_init(void)
{
#ifdef CONFIG_PROC_FS
- register_proc_table(root_table, proc_sys_root);
+ register_proc_table(root_table, proc_sys_root, &root_table_header);
init_irq_proc();
#endif
}
@@ -1004,6 +1045,7 @@
void __user *newval, size_t newlen)
{
struct list_head *tmp;
+ int error = -ENOTDIR;
if (nlen <= 0 || nlen >= CTL_MAXNAME)
return -ENOTDIR;
@@ -1012,20 +1054,30 @@
if (!oldlenp || get_user(old_len, oldlenp))
return -EFAULT;
}
+ spin_lock(&sysctl_lock);
tmp = &root_table_header.ctl_entry;
do {
struct ctl_table_header *head =
list_entry(tmp, struct ctl_table_header, ctl_entry);
void *context = NULL;
- int error = parse_table(name, nlen, oldval, oldlenp,
+
+ if (!use_table(head))
+ continue;
+
+ spin_unlock(&sysctl_lock);
+
+ error = parse_table(name, nlen, oldval, oldlenp,
newval, newlen, head->ctl_table,
&context);
kfree(context);
+
+ spin_lock(&sysctl_lock);
+ unuse_table(head);
if (error != -ENOTDIR)
- return error;
- tmp = tmp->next;
- } while (tmp != &root_table_header.ctl_entry);
- return -ENOTDIR;
+ break;
+ } while ((tmp = tmp->next) != &root_table_header.ctl_entry);
+ spin_unlock(&sysctl_lock);
+ return error;
}
asmlinkage long sys_sysctl(struct __sysctl_args __user *args)
@@ -1236,12 +1288,16 @@
return NULL;
tmp->ctl_table = table;
INIT_LIST_HEAD(&tmp->ctl_entry);
+ tmp->used = 0;
+ tmp->unregistering = NULL;
+ spin_lock(&sysctl_lock);
if (insert_at_head)
list_add(&tmp->ctl_entry, &root_table_header.ctl_entry);
else
list_add_tail(&tmp->ctl_entry, &root_table_header.ctl_entry);
+ spin_unlock(&sysctl_lock);
#ifdef CONFIG_PROC_FS
- register_proc_table(table, proc_sys_root);
+ register_proc_table(table, proc_sys_root, tmp);
#endif
return tmp;
}
@@ -1255,10 +1311,13 @@
*/
void unregister_sysctl_table(struct ctl_table_header * header)
{
- list_del(&header->ctl_entry);
+ might_sleep();
+ spin_lock(&sysctl_lock);
+ start_unregistering(header);
#ifdef CONFIG_PROC_FS
unregister_proc_table(header->ctl_table, proc_sys_root);
#endif
+ spin_unlock(&sysctl_lock);
kfree(header);
}
@@ -1269,7 +1328,7 @@
#ifdef CONFIG_PROC_FS
/* Scan the sysctl entries in table and add them all into /proc */
-static void register_proc_table(ctl_table * table, struct proc_dir_entry *root)
+static void register_proc_table(ctl_table * table, struct proc_dir_entry *root, void *set)
{
struct proc_dir_entry *de;
int len;
@@ -1305,13 +1364,14 @@
de = create_proc_entry(table->procname, mode, root);
if (!de)
continue;
+ de->set = set;
de->data = (void *) table;
if (table->proc_handler)
de->proc_fops = &proc_sys_file_operations;
}
table->de = de;
if (de->mode & S_IFDIR)
- register_proc_table(table->child, de);
+ register_proc_table(table->child, de, set);
}
}
@@ -1336,6 +1396,13 @@
continue;
}
+ /*
+ * In any case, mark the entry as goner; we'll keep it
+ * around if it's busy, but we'll know to do nothing with
+ * its fields. We are under sysctl_lock here.
+ */
+ de->data = NULL;
+
/* Don't unregister proc entries that are still being used.. */
if (atomic_read(&de->count))
continue;
@@ -1349,27 +1416,38 @@
size_t count, loff_t *ppos)
{
int op;
- struct proc_dir_entry *de;
+ struct proc_dir_entry *de = PDE(file->f_dentry->d_inode);
struct ctl_table *table;
size_t res;
- ssize_t error;
+ ssize_t error = -ENOTDIR;
- de = PDE(file->f_dentry->d_inode);
- if (!de || !de->data)
- return -ENOTDIR;
- table = (struct ctl_table *) de->data;
- if (!table || !table->proc_handler)
- return -ENOTDIR;
- op = (write ? 002 : 004);
- if (ctl_perm(table, op))
- return -EPERM;
-
- res = count;
-
- error = (*table->proc_handler) (table, write, file, buf, &res, ppos);
- if (error)
- return error;
- return res;
+ spin_lock(&sysctl_lock);
+ if (de && de->data && use_table(de->set)) {
+ /*
+ * at that point we know that sysctl was not unregistered
+ * and won't be until we finish
+ */
+ spin_unlock(&sysctl_lock);
+ table = (struct ctl_table *) de->data;
+ if (!table || !table->proc_handler)
+ goto out;
+ error = -EPERM;
+ op = (write ? 002 : 004);
+ if (ctl_perm(table, op))
+ goto out;
+
+ /* careful: calling conventions are nasty here */
+ res = count;
+ error = (*table->proc_handler)(table, write, file,
+ buf, &res, ppos);
+ if (!error)
+ error = res;
+ out:
+ spin_lock(&sysctl_lock);
+ unuse_table(de->set);
+ }
+ spin_unlock(&sysctl_lock);
+ return error;
}
static int proc_opensys(struct inode *inode, struct file *file)
