[NETFILTER]: ip_tables: fix compat copy race

When copying entries to user, the kernel makes two passes through the
data, first copying all the entries, then fixing up names and counters.
On the second pass it copies the kernel and match data from userspace
to the kernel again to find the corresponding structures, expecting
that kernel pointers contained in the data are still valid.

This is obviously broken, fix by avoiding the second pass completely
and fixing names and counters while dumping the ruleset, using the
kernel-internal data structures.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 45 deletions

diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index 4b10b98640ac..b9b189c26208 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -1492,8 +1492,10 @@ static inline int compat_copy_match_to_user(struct ipt_entry_match *m,
         return xt_compat_match_to_user(m, dstptr, size);
 }
 
-static int compat_copy_entry_to_user(struct ipt_entry *e,
-                void __user **dstptr, compat_uint_t *size)
+static int
+compat_copy_entry_to_user(struct ipt_entry *e, void __user **dstptr,
+                          compat_uint_t *size, struct xt_counters *counters,
+                          unsigned int *i)
 {
         struct ipt_entry_target *t;
         struct compat_ipt_entry __user *ce;
@@ -1507,6 +1509,9 @@ static int compat_copy_entry_to_user(struct ipt_entry *e,
         if (copy_to_user(ce, e, sizeof(struct ipt_entry)))
                 goto out;
 
+        if (copy_to_user(&ce->counters, &counters[*i], sizeof(counters[*i])))
+                goto out;
+
         *dstptr += sizeof(struct compat_ipt_entry);
         ret = IPT_MATCH_ITERATE(e, compat_copy_match_to_user, dstptr, size);
         target_offset = e->target_offset - (origsize - *size);
@@ -1522,6 +1527,8 @@ static int compat_copy_entry_to_user(struct ipt_entry *e,
                 goto out;
         if (put_user(next_offset, &ce->next_offset))
                 goto out;
+
+        (*i)++;
         return 0;
 out:
         return ret;
@@ -1937,14 +1944,13 @@ struct compat_ipt_get_entries
 static int compat_copy_entries_to_user(unsigned int total_size,
                      struct xt_table *table, void __user *userptr)
 {
-        unsigned int off, num;
-        struct compat_ipt_entry e;
         struct xt_counters *counters;
         struct xt_table_info *private = table->private;
         void __user *pos;
         unsigned int size;
         int ret = 0;
         void *loc_cpu_entry;
+        unsigned int i = 0;
 
         counters = alloc_counters(table);
         if (IS_ERR(counters))
@@ -1958,48 +1964,9 @@ static int compat_copy_entries_to_user(unsigned int total_size,
         pos = userptr;
         size = total_size;
         ret = IPT_ENTRY_ITERATE(loc_cpu_entry, total_size,
-                        compat_copy_entry_to_user, &pos, &size);
-        if (ret)
-                goto free_counters;
-
-        /* ... then go back and fix counters and names */
-        for (off = 0, num = 0; off < size; off += e.next_offset, num++) {
-                unsigned int i;
-                struct ipt_entry_match m;
-                struct ipt_entry_target t;
+                                compat_copy_entry_to_user,
+                                &pos, &size, counters, &i);
 
-                ret = -EFAULT;
-                if (copy_from_user(&e, userptr + off,
-                                        sizeof(struct compat_ipt_entry)))
-                        goto free_counters;
-                if (copy_to_user(userptr + off +
-                        offsetof(struct compat_ipt_entry, counters),
-                         &counters[num], sizeof(counters[num])))
-                        goto free_counters;
-
-                for (i = sizeof(struct compat_ipt_entry);
-                                i < e.target_offset; i += m.u.match_size) {
-                        if (copy_from_user(&m, userptr + off + i,
-                                        sizeof(struct ipt_entry_match)))
-                                goto free_counters;
-                        if (copy_to_user(userptr + off + i +
-                                offsetof(struct ipt_entry_match, u.user.name),
-                                m.u.kernel.match->name,
-                                strlen(m.u.kernel.match->name) + 1))
-                                goto free_counters;
-                }
-
-                if (copy_from_user(&t, userptr + off + e.target_offset,
-                                        sizeof(struct ipt_entry_target)))
-                        goto free_counters;
-                if (copy_to_user(userptr + off + e.target_offset +
-                        offsetof(struct ipt_entry_target, u.user.name),
-                        t.u.kernel.target->name,
-                        strlen(t.u.kernel.target->name) + 1))
-                        goto free_counters;
-        }
-        ret = 0;
-free_counters:
         vfree(counters);
         return ret;
 }