bpf: sockmap: Require attach_bpf_fd when detaching a program

The sockmap code currently ignores the value of attach_bpf_fd when
detaching a program. This is contrary to the usual behaviour of
checking that attach_bpf_fd represents the currently attached
program.

Ensure that attach_bpf_fd is indeed the currently attached
program. It turns out that all sockmap selftests already do this,
which indicates that this is unlikely to cause breakage.

Fixes: 38506f4bbc9d ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200629095630.7933-5-lmb@cloudflare.com

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 07052d44bca1c692cb6f360dd614c4c6ce854016..9750a1902ee503814ce83e6b890837b1c673bdc4 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1543,13 +1543,16 @@ static inline void bpf_map_offload_map_free(struct bpf_map *map)
 #endif /* CONFIG_NET && CONFIG_BPF_SYSCALL */
 
 #if defined(CONFIG_BPF_STREAM_PARSER)
-int sock_map_prog_update(struct bpf_map *map, struct bpf_prog *prog, u32 which);
+int sock_map_prog_update(struct bpf_map *map, struct bpf_prog *prog,
+                        struct bpf_prog *old, u32 which);
 int sock_map_get_from_fd(const union bpf_attr *attr, struct bpf_prog *prog);
+int sock_map_prog_detach(const union bpf_attr *attr, enum bpf_prog_type ptype);
 void sock_map_unhash(struct sock *sk);
 void sock_map_close(struct sock *sk, long timeout);
 #else
 static inline int sock_map_prog_update(struct bpf_map *map,
-                                      struct bpf_prog *prog, u32 which)
+                                      struct bpf_prog *prog,
+                                      struct bpf_prog *old, u32 which)
 {
        return -EOPNOTSUPP;
 }
@@ -1559,6 +1562,12 @@ static inline int sock_map_get_from_fd(const union bpf_attr *attr,
 {
        return -EINVAL;
 }
+
+static inline int sock_map_prog_detach(const union bpf_attr *attr,
+                                      enum bpf_prog_type ptype)
+{
+       return -EOPNOTSUPP;
+}
 #endif /* CONFIG_BPF_STREAM_PARSER */
 
 #if defined(CONFIG_INET) && defined(CONFIG_BPF_SYSCALL)

diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
index 08674cd14d5a5581d383daeb9c745ed61ff58e1d..1e9ed840b9fc101087c860dd6879de95afb950d3 100644 (file)
--- a/include/linux/skmsg.h
+++ b/include/linux/skmsg.h
@@ -430,6 +430,19 @@ static inline void psock_set_prog(struct bpf_prog **pprog,
                bpf_prog_put(prog);
 }
 
+static inline int psock_replace_prog(struct bpf_prog **pprog,
+                                    struct bpf_prog *prog,
+                                    struct bpf_prog *old)
+{
+       if (cmpxchg(pprog, old, prog) != old)
+               return -ENOENT;
+
+       if (old)
+               bpf_prog_put(old);
+
+       return 0;
+}
+
 static inline void psock_progs_drop(struct sk_psock_progs *progs)
 {
        psock_set_prog(&progs->msg_parser, NULL);

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 28c6ef7590370af7bc075deca251182f7bf2f618..a74fce8ce043f410ac3df9be9f9dfacf17016faf 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2893,7 +2893,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
        switch (ptype) {
        case BPF_PROG_TYPE_SK_MSG:
        case BPF_PROG_TYPE_SK_SKB:
-               return sock_map_get_from_fd(attr, NULL);
+               return sock_map_prog_detach(attr, ptype);
        case BPF_PROG_TYPE_LIRC_MODE2:
                return lirc_prog_detach(attr);
        case BPF_PROG_TYPE_FLOW_DISSECTOR:

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 58016a5c63ff8a00ece1080e61222a435558d3a3..0971f17e8e5429427d48f60524eaf4c9d8f292f9 100644 (file)
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -77,7 +77,42 @@ int sock_map_get_from_fd(const union bpf_attr *attr, struct bpf_prog *prog)
        map = __bpf_map_get(f);
        if (IS_ERR(map))
                return PTR_ERR(map);
-       ret = sock_map_prog_update(map, prog, attr->attach_type);
+       ret = sock_map_prog_update(map, prog, NULL, attr->attach_type);
+       fdput(f);
+       return ret;
+}
+
+int sock_map_prog_detach(const union bpf_attr *attr, enum bpf_prog_type ptype)
+{
+       u32 ufd = attr->target_fd;
+       struct bpf_prog *prog;
+       struct bpf_map *map;
+       struct fd f;
+       int ret;
+
+       if (attr->attach_flags || attr->replace_bpf_fd)
+               return -EINVAL;
+
+       f = fdget(ufd);
+       map = __bpf_map_get(f);
+       if (IS_ERR(map))
+               return PTR_ERR(map);
+
+       prog = bpf_prog_get(attr->attach_bpf_fd);
+       if (IS_ERR(prog)) {
+               ret = PTR_ERR(prog);
+               goto put_map;
+       }
+
+       if (prog->type != ptype) {
+               ret = -EINVAL;
+               goto put_prog;
+       }
+
+       ret = sock_map_prog_update(map, NULL, prog, attr->attach_type);
+put_prog:
+       bpf_prog_put(prog);
+put_map:
        fdput(f);
        return ret;
 }
@@ -1206,27 +1241,32 @@ static struct sk_psock_progs *sock_map_progs(struct bpf_map *map)
 }
 
 int sock_map_prog_update(struct bpf_map *map, struct bpf_prog *prog,
-                        u32 which)
+                        struct bpf_prog *old, u32 which)
 {
        struct sk_psock_progs *progs = sock_map_progs(map);
+       struct bpf_prog **pprog;
 
        if (!progs)
                return -EOPNOTSUPP;
 
        switch (which) {
        case BPF_SK_MSG_VERDICT:
-               psock_set_prog(&progs->msg_parser, prog);
+               pprog = &progs->msg_parser;
                break;
        case BPF_SK_SKB_STREAM_PARSER:
-               psock_set_prog(&progs->skb_parser, prog);
+               pprog = &progs->skb_parser;
                break;
        case BPF_SK_SKB_STREAM_VERDICT:
-               psock_set_prog(&progs->skb_verdict, prog);
+               pprog = &progs->skb_verdict;
                break;
        default:
                return -EOPNOTSUPP;
        }
 
+       if (old)
+               return psock_replace_prog(pprog, prog, old);
+
+       psock_set_prog(pprog, prog);
        return 0;
 }