netdev - [iproute PATCH v2] iproute: restrict hoplimit values to be in range [0;255]

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Date:	Tue, 24 Nov 2015 15:45:31 +0100
From:	Phil Sutter <phil@....cc>
To:	Stephen Hemminger <shemming@...cade.com>
Cc:	netdev@...r.kernel.org
Subject: [iproute PATCH v2] iproute: restrict hoplimit values to be in range [0;255]

Technically, the range of possible hoplimit values are defined by IPv4
and IPv6 header formats. Both define the field to be eight bits in size,
which leads to a value range of [0;255]. Setting a packet's hoplimit
field to 0 though makes not much sense, as the next hop would
immediately drop the packet. Therefore Linux uses 0 as a special value
indicating to use the system's default hoplimit (configurable via
sysctl). In iproute, setting the hoplimit of a route to 0 is equivalent
to omitting the hoplimit parameter alltogether, so it is actually not
necessary to allow that value to be specified, but keep it anyway for
backwards compatibility.

Signed-off-by: Phil Sutter <phil@....cc>
---
Changes since v1:
- Allow hoplimit 0 for backwards compatibility.
- Adjust commit message accordingly.
---
 ip/iproute.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ip/iproute.c b/ip/iproute.c
index c0ef7bf..aed1038 100644
--- a/ip/iproute.c
+++ b/ip/iproute.c
@@ -931,7 +931,7 @@ static int iproute_modify(int cmd, unsigned flags, int argc, char **argv)
 				mxlock |= (1<<RTAX_HOPLIMIT);
 				NEXT_ARG();
 			}
-			if (get_unsigned(&hoplimit, *argv, 0))
+			if (get_unsigned(&hoplimit, *argv, 0) || hoplimit > 255)
 				invarg("\"hoplimit\" value is invalid\n", *argv);
 			rta_addattr32(mxrta, sizeof(mxbuf), RTAX_HOPLIMIT, hoplimit);
 		} else if (strcmp(*argv, "advmss") == 0) {
-- 
2.5.0

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