Commit 330d57fb authored by Al Viro's avatar Al Viro Committed by Linus Torvalds

[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: default avatarGreg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 8546df6f
......@@ -592,12 +592,15 @@ int appldata_register_ops(struct appldata_ops *ops)
*/
void appldata_unregister_ops(struct appldata_ops *ops)
{
void *table;
spin_lock(&appldata_ops_lock);
unregister_sysctl_table(ops->sysctl_header);
list_del(&ops->list);
kfree(ops->ctl_table);
/* at that point any incoming access will fail */
table = ops->ctl_table;
ops->ctl_table = NULL;
spin_unlock(&appldata_ops_lock);
unregister_sysctl_table(ops->sysctl_header);
kfree(table);
P_INFO("%s-ops unregistered!\n", ops->name);
}
/********************** module-ops management <END> **************************/
......
......@@ -66,6 +66,7 @@ struct proc_dir_entry {
write_proc_t *write_proc;
atomic_t count; /* use count */
int deleted; /* delete flag */
void *set;
};
struct kcore_list {
......
......@@ -24,6 +24,7 @@
#include <linux/compiler.h>
struct file;
struct completion;
#define CTL_MAXNAME 10 /* how many path components do we allow in a
call to sysctl? In other words, what is
......@@ -925,6 +926,8 @@ struct ctl_table_header
{
ctl_table *ctl_table;
struct list_head ctl_entry;
int used;
struct completion *unregistering;
};
struct ctl_table_header * register_sysctl_table(ctl_table * table,
......
......@@ -169,7 +169,7 @@ struct file_operations proc_sys_file_operations = {
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 @@ static ctl_table dev_table[] = {
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 @@ int do_sysctl(int __user *name, int nlen, void __user *oldval, size_t __user *ol
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 @@ int do_sysctl(int __user *name, int nlen, void __user *oldval, size_t __user *ol
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 @@ struct ctl_table_header *register_sysctl_table(ctl_table * table,
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 @@ struct ctl_table_header *register_sysctl_table(ctl_table * table,
*/
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 @@ void unregister_sysctl_table(struct ctl_table_header * header)
#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 @@ static void register_proc_table(ctl_table * table, struct proc_dir_entry *root)
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 @@ static void unregister_proc_table(ctl_table * table, struct proc_dir_entry *root
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 @@ static ssize_t do_rw_proc(int write, struct file * file, char __user * buf,
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;
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;
ssize_t error = -ENOTDIR;
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)
......
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