tun: fix return value when the number of iovs exceeds MAX_SKB_FRAGS

stable inclusion
from stable-5.10.7
commit e3cbce80be894293d5d90b657df0ea33d754068c
bugzilla: 47429

--------------------------------

[ Upstream commit 950271d7 ]

Currently the tun_napi_alloc_frags() function returns -ENOMEM when the
number of iovs exceeds MAX_SKB_FRAGS + 1. However this is inappropriate,
we should use -EMSGSIZE instead of -ENOMEM.

The following distinctions are matters:
1. the caller need to drop the bad packet when -EMSGSIZE is returned,
   which means meeting a persistent failure.
2. the caller can try again when -ENOMEM is returned, which means
   meeting a transient failure.

Fixes: 90e33d45 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: NYunjian Wang <wangyunjian@huawei.com>
Acked-by: NWillem de Bruijn <willemb@google.com>
Acked-by: NJason Wang <jasowang@redhat.com>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/1608864736-24332-1-git-send-email-wangyunjian@huawei.comSigned-off-by: NJakub Kicinski <kuba@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

drivers/net/tun.c

@@ -1401,7 +1401,7 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile,
 	int i;
 
 	if (it->nr_segs > MAX_SKB_FRAGS + 1)
-		return ERR_PTR(-ENOMEM);
+		return ERR_PTR(-EMSGSIZE);
 
 	local_bh_disable();
 	skb = napi_get_frags(&tfile->napi);