net: filter: keep original BPF program around

In order to open up the possibility to internally transform a BPF program
into an alternative and possibly non-trivial reversible representation, we
need to keep the original BPF program around, so that it can be passed back
to user space w/o the need of a complex decoder.

The reason for that use case resides in commit a8fc92778080 ("sk-filter:
Add ability to get socket filter program (v2)"), that is, the ability
to retrieve the currently attached BPF filter from a given socket used
mainly by the checkpoint-restore project, for example.

Therefore, we add two helpers sk_{store,release}_orig_filter for taking
care of that. In the sk_unattached_filter_create() case, there's no such
possibility/requirement to retrieve a loaded BPF program. Therefore, we
can spare us the work in that case.

This approach will simplify and slightly speed up both, sk_get_filter()
and sock_diag_put_filterinfo() handlers as we won't need to successively
decode filters anymore through sk_decode_filter(). As we still need
sk_decode_filter() later on, we're keeping it around.

Joint work with Alexei Starovoitov.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 93 insertions, 31 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index e65e23087367..93a9792e27bc 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -19,14 +19,19 @@ struct compat_sock_fprog {
 };
 #endif
 
+struct sock_fprog_kern {
+        u16                     len;
+        struct sock_filter      *filter;
+};
+
 struct sk_buff;
 struct sock;
 
-struct sk_filter
-{
+struct sk_filter {
         atomic_t                refcnt;
         u32                     jited:1,        /* Is our filter JIT'ed? */
                                 len:31;         /* Number of filter blocks */
+        struct sock_fprog_kern  *orig_prog;     /* Original BPF program */
         struct rcu_head         rcu;
         unsigned int            (*bpf_func)(const struct sk_buff *skb,
                                             const struct sock_filter *filter);
@@ -42,14 +47,20 @@ static inline unsigned int sk_filter_size(unsigned int proglen)
                    offsetof(struct sk_filter, insns[proglen]));
 }
 
+#define sk_filter_proglen(fprog)                        \
+                (fprog->len * sizeof(fprog->filter[0]))
+
 extern int sk_filter(struct sock *sk, struct sk_buff *skb);
 extern unsigned int sk_run_filter(const struct sk_buff *skb,
                                   const struct sock_filter *filter);
+
 extern int sk_unattached_filter_create(struct sk_filter **pfp,
                                        struct sock_fprog *fprog);
 extern void sk_unattached_filter_destroy(struct sk_filter *fp);
+
 extern int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk);
 extern int sk_detach_filter(struct sock *sk);
+
 extern int sk_chk_filter(struct sock_filter *filter, unsigned int flen);
 extern int sk_get_filter(struct sock *sk, struct sock_filter __user *filter, unsigned len);
 extern void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to);
diff --git a/net/core/filter.c b/net/core/filter.c
index bb3c76458ca9..9730e7fe4770 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -629,6 +629,37 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen)
 }
 EXPORT_SYMBOL(sk_chk_filter);
 
+static int sk_store_orig_filter(struct sk_filter *fp,
+                                const struct sock_fprog *fprog)
+{
+        unsigned int fsize = sk_filter_proglen(fprog);
+        struct sock_fprog_kern *fkprog;
+
+        fp->orig_prog = kmalloc(sizeof(*fkprog), GFP_KERNEL);
+        if (!fp->orig_prog)
+                return -ENOMEM;
+
+        fkprog = fp->orig_prog;
+        fkprog->len = fprog->len;
+        fkprog->filter = kmemdup(fp->insns, fsize, GFP_KERNEL);
+        if (!fkprog->filter) {
+                kfree(fp->orig_prog);
+                return -ENOMEM;
+        }
+
+        return 0;
+}
+
+static void sk_release_orig_filter(struct sk_filter *fp)
+{
+        struct sock_fprog_kern *fprog = fp->orig_prog;
+
+        if (fprog) {
+                kfree(fprog->filter);
+                kfree(fprog);
+        }
+}
+
 /**
  *      sk_filter_release_rcu - Release a socket filter by rcu_head
  *      @rcu: rcu_head that contains the sk_filter to free
@@ -637,6 +668,7 @@ void sk_filter_release_rcu(struct rcu_head *rcu)
 {
         struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
 
+        sk_release_orig_filter(fp);
         bpf_jit_free(fp);
 }
 EXPORT_SYMBOL(sk_filter_release_rcu);
@@ -669,8 +701,8 @@ static int __sk_prepare_filter(struct sk_filter *fp)
 int sk_unattached_filter_create(struct sk_filter **pfp,
                                 struct sock_fprog *fprog)
 {
+        unsigned int fsize = sk_filter_proglen(fprog);
         struct sk_filter *fp;
-        unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
         int err;
 
         /* Make sure new filter is there and in the right amounts. */
@@ -680,10 +712,16 @@ int sk_unattached_filter_create(struct sk_filter **pfp,
         fp = kmalloc(sk_filter_size(fprog->len), GFP_KERNEL);
         if (!fp)
                 return -ENOMEM;
+
         memcpy(fp->insns, fprog->filter, fsize);
 
         atomic_set(&fp->refcnt, 1);
         fp->len = fprog->len;
+        /* Since unattached filters are not copied back to user
+         * space through sk_get_filter(), we do not need to hold
+         * a copy here, and can spare us the work.
+         */
+        fp->orig_prog = NULL;
 
         err = __sk_prepare_filter(fp);
         if (err)
@@ -716,7 +754,7 @@ EXPORT_SYMBOL_GPL(sk_unattached_filter_destroy);
 int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 {
         struct sk_filter *fp, *old_fp;
-        unsigned int fsize = sizeof(struct sock_filter) * fprog->len;
+        unsigned int fsize = sk_filter_proglen(fprog);
         unsigned int sk_fsize = sk_filter_size(fprog->len);
         int err;
 
@@ -730,6 +768,7 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
         fp = sock_kmalloc(sk, sk_fsize, GFP_KERNEL);
         if (!fp)
                 return -ENOMEM;
+
         if (copy_from_user(fp->insns, fprog->filter, fsize)) {
                 sock_kfree_s(sk, fp, sk_fsize);
                 return -EFAULT;
@@ -738,6 +777,12 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
         atomic_set(&fp->refcnt, 1);
         fp->len = fprog->len;
 
+        err = sk_store_orig_filter(fp, fprog);
+        if (err) {
+                sk_filter_uncharge(sk, fp);
+                return -ENOMEM;
+        }
+
         err = __sk_prepare_filter(fp);
         if (err) {
                 sk_filter_uncharge(sk, fp);
@@ -750,6 +795,7 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
 
         if (old_fp)
                 sk_filter_uncharge(sk, old_fp);
+
         return 0;
 }
 EXPORT_SYMBOL_GPL(sk_attach_filter);
@@ -769,6 +815,7 @@ int sk_detach_filter(struct sock *sk)
                 sk_filter_uncharge(sk, filter);
                 ret = 0;
         }
+
         return ret;
 }
 EXPORT_SYMBOL_GPL(sk_detach_filter);
@@ -851,34 +898,41 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to)
         to->k = filt->k;
 }
 
-int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf, unsigned int len)
+int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf,
+                  unsigned int len)
 {
+        struct sock_fprog_kern *fprog;
         struct sk_filter *filter;
-        int i, ret;
+        int ret = 0;
 
         lock_sock(sk);
         filter = rcu_dereference_protected(sk->sk_filter,
-                        sock_owned_by_user(sk));
-        ret = 0;
+                                           sock_owned_by_user(sk));
         if (!filter)
                 goto out;
-        ret = filter->len;
+
+        /* We're copying the filter that has been originally attached,
+         * so no conversion/decode needed anymore.
+         */
+        fprog = filter->orig_prog;
+
+        ret = fprog->len;
         if (!len)
+                /* User space only enquires number of filter blocks. */
                 goto out;
+
         ret = -EINVAL;
-        if (len < filter->len)
+        if (len < fprog->len)
                 goto out;
 
         ret = -EFAULT;
-        for (i = 0; i < filter->len; i++) {
-                struct sock_filter fb;
-
-                sk_decode_filter(&filter->insns[i], &fb);
-                if (copy_to_user(&ubuf[i], &fb, sizeof(fb)))
-                        goto out;
-        }
+        if (copy_to_user(ubuf, fprog->filter, sk_filter_proglen(fprog)))
+                goto out;
 
-        ret = filter->len;
+        /* Instead of bytes, the API requests to return the number
+         * of filter blocks.
+         */
+        ret = fprog->len;
 out:
         release_sock(sk);
         return ret;
diff --git a/net/core/sock_diag.c b/net/core/sock_diag.c
index a0e9cf6379de..d7af18859322 100644
--- a/net/core/sock_diag.c
+++ b/net/core/sock_diag.c
@@ -52,9 +52,10 @@ EXPORT_SYMBOL_GPL(sock_diag_put_meminfo);
 int sock_diag_put_filterinfo(struct user_namespace *user_ns, struct sock *sk,
                              struct sk_buff *skb, int attrtype)
 {
-        struct nlattr *attr;
+        struct sock_fprog_kern *fprog;
         struct sk_filter *filter;
-        unsigned int len;
+        struct nlattr *attr;
+        unsigned int flen;
         int err = 0;
 
         if (!ns_capable(user_ns, CAP_NET_ADMIN)) {
@@ -63,24 +64,20 @@ int sock_diag_put_filterinfo(struct user_namespace *user_ns, struct sock *sk,
         }
 
         rcu_read_lock();
-
         filter = rcu_dereference(sk->sk_filter);
-        len = filter ? filter->len * sizeof(struct sock_filter) : 0;
+        if (!filter)
+                goto out;
 
-        attr = nla_reserve(skb, attrtype, len);
+        fprog = filter->orig_prog;
+        flen = sk_filter_proglen(fprog);
+
+        attr = nla_reserve(skb, attrtype, flen);
         if (attr == NULL) {
                 err = -EMSGSIZE;
                 goto out;
         }
 
-        if (filter) {
-                struct sock_filter *fb = (struct sock_filter *)nla_data(attr);
-                int i;
-
-                for (i = 0; i < filter->len; i++, fb++)
-                        sk_decode_filter(&filter->insns[i], fb);
-        }
-
+        memcpy(nla_data(attr), fprog->filter, flen);
 out:
         rcu_read_unlock();
         return err;