[PATCH 4.19 26/77] tun: fix return value when the number of iovs exceeds MAX_SKB_FRAGS

[Greg Kroah-Hartman]

From: Yunjian Wang <wangyunjian@xxxxxxxxxx>

[ Upstream commit 950271d7cc0b4546af3549d8143c4132d6e1f138 ]

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: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: Yunjian Wang <wangyunjian@xxxxxxxxxx>
Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Link: https://lore.kernel.org/r/1608864736-24332-1-git-send-email-wangyunjian@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/tun.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1450,7 +1450,7 @@ static struct sk_buff *tun_napi_alloc_fr
 	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);