[RFC PATCH 4/6] ah6: Create function __zero_out_mutable_opts

[Tom Herbert <tom@herbertland.com>]

This is an adaptation of zero_out_mutable_opts that takes three
additional arguments: offset of the TLVs, a mask to locate the
mutable bit in the TLV type, and the type value for single byte
padding.

zero_out_mutable_opts calls the new function and sets the arguments
appropriate to Hop-by-Hop and Destination Options. The function will
be used to support zeroing out mutable SRH TLVs' data with the
appropriate arguments for SRH TLVs.

Signed-off-by: Tom Herbert <tom@quantonium.net>
---
 net/ipv6/ah6.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c
index 68b9e92..1e80157 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c
@@ -102,32 +102,28 @@ static inline struct scatterlist *ah_req_sg(struct crypto_ahash *ahash,
 			     __alignof__(struct scatterlist));
 }
 
-static bool zero_out_mutable_opts(struct ipv6_opt_hdr *opthdr)
+static bool __zero_out_mutable_opts(struct ipv6_opt_hdr *opthdr, int off,
+				    unsigned char mut_bit, unsigned char pad1)
 {
 	u8 *opt = (u8 *)opthdr;
 	int len = ipv6_optlen(opthdr);
-	int off = 0;
 	int optlen = 0;
 
-	off += 2;
-	len -= 2;
+	len -= off;
 
 	while (len > 0) {
-
-		switch (opt[off]) {
-
-		case IPV6_TLV_PAD1:
+		if (opt[off] == pad1) {
 			optlen = 1;
-			break;
-		default:
+		} else {
 			if (len < 2)
 				goto bad;
-			optlen = opt[off+1]+2;
+
+			optlen = opt[off + 1] + 2;
 			if (len < optlen)
 				goto bad;
-			if (opt[off] & 0x20)
-				memset(&opt[off+2], 0, opt[off+1]);
-			break;
+
+			if (opt[off] & mut_bit)
+				memset(&opt[off + 2], 0, opt[off + 1]);
 		}
 
 		off += optlen;
@@ -140,6 +136,11 @@ static bool zero_out_mutable_opts(struct ipv6_opt_hdr *opthdr)
 	return false;
 }
 
+static bool zero_out_mutable_opts(struct ipv6_opt_hdr *opthdr)
+{
+	return __zero_out_mutable_opts(opthdr, 2, 0x20, IPV6_TLV_PAD1);
+}
+
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
 /**
  *	ipv6_rearrange_destopt - rearrange IPv6 destination options header
-- 
2.7.4