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Subject[PATCH 4/5] bpf: sockmap, sockhash: return file descriptors from privileged lookup
Date
Allow callers with CAP_NET_ADMIN to retrieve file descriptors from a
sockmap and sockhash. O_CLOEXEC is enforced on all fds.

Without this, it's difficult to resize or otherwise rebuild existing
sockmap or sockhashes.

Suggested-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
---
net/core/sock_map.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 03e04426cd21..3228936aa31e 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -347,12 +347,31 @@ static void *sock_map_lookup(struct bpf_map *map, void *key)
static int __sock_map_copy_value(struct bpf_map *map, struct sock *sk,
void *value)
{
+ struct file *file;
+ int fd;
+
switch (map->value_size) {
case sizeof(u64):
sock_gen_cookie(sk);
*(u64 *)value = atomic64_read(&sk->sk_cookie);
return 0;

+ case sizeof(u32):
+ if (!capable(CAP_NET_ADMIN))
+ return -EPERM;
+
+ fd = get_unused_fd_flags(O_CLOEXEC);
+ if (unlikely(fd < 0))
+ return fd;
+
+ read_lock_bh(&sk->sk_callback_lock);
+ file = get_file(sk->sk_socket->file);
+ read_unlock_bh(&sk->sk_callback_lock);
+
+ fd_install(fd, file);
+ *(u32 *)value = fd;
+ return 0;
+
default:
return -ENOSPC;
}
--
2.20.1
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