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-rw-r--r--net/netlink/af_netlink.c34
1 files changed, 22 insertions, 12 deletions
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 8f060d7f9a0e..0a49a8c7c564 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2785,6 +2785,7 @@ static int netlink_dump(struct sock *sk)
struct sk_buff *skb = NULL;
struct nlmsghdr *nlh;
int len, err = -ENOBUFS;
+ int alloc_min_size;
int alloc_size;
mutex_lock(nlk->cb_mutex);
@@ -2793,9 +2794,6 @@ static int netlink_dump(struct sock *sk)
goto errout_skb;
}
- cb = &nlk->cb;
- alloc_size = max_t(int, cb->min_dump_alloc, NLMSG_GOODSIZE);
-
if (!netlink_rx_is_mmaped(sk) &&
atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
goto errout_skb;
@@ -2805,23 +2803,35 @@ static int netlink_dump(struct sock *sk)
* to reduce number of system calls on dump operations, if user
* ever provided a big enough buffer.
*/
- if (alloc_size < nlk->max_recvmsg_len) {
- skb = netlink_alloc_skb(sk,
- nlk->max_recvmsg_len,
- nlk->portid,
+ cb = &nlk->cb;
+ alloc_min_size = max_t(int, cb->min_dump_alloc, NLMSG_GOODSIZE);
+
+ if (alloc_min_size < nlk->max_recvmsg_len) {
+ alloc_size = nlk->max_recvmsg_len;
+ skb = netlink_alloc_skb(sk, alloc_size, nlk->portid,
GFP_KERNEL |
__GFP_NOWARN |
__GFP_NORETRY);
- /* available room should be exact amount to avoid MSG_TRUNC */
- if (skb)
- skb_reserve(skb, skb_tailroom(skb) -
- nlk->max_recvmsg_len);
}
- if (!skb)
+ if (!skb) {
+ alloc_size = alloc_min_size;
skb = netlink_alloc_skb(sk, alloc_size, nlk->portid,
GFP_KERNEL);
+ }
if (!skb)
goto errout_skb;
+
+ /* Trim skb to allocated size. User is expected to provide buffer as
+ * large as max(min_dump_alloc, 16KiB (mac_recvmsg_len capped at
+ * netlink_recvmsg())). dump will pack as many smaller messages as
+ * could fit within the allocated skb. skb is typically allocated
+ * with larger space than required (could be as much as near 2x the
+ * requested size with align to next power of 2 approach). Allowing
+ * dump to use the excess space makes it difficult for a user to have a
+ * reasonable static buffer based on the expected largest dump of a
+ * single netdev. The outcome is MSG_TRUNC error.
+ */
+ skb_reserve(skb, skb_tailroom(skb) - alloc_size);
netlink_skb_set_owner_r(skb, sk);
len = cb->dump(skb, cb);