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>

diff --git a/include/linux/filter.h b/include/linux/filter.h
index e65e230873679285cdba21bee8f9c07429ef626d..93a9792e27bce628f9393b6bc5519f90e27ba139 100644 (file)
--- 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 bb3c76458ca9cc3c2f6aefc8022a224055c5fa65..9730e7fe477002d76b576d9950818d988a868a3f 100644 (file)
--- 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 a0e9cf6379de3eac8ac1182c3be73e8d140b4a1b..d7af1885932269eb9f4196fe1211a6d09e298b97 100644 (file)
--- 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;