Revert this upstream commit:

commit 9a0cc8c1bd7645bf3c988890ffb59639c07a5812

Author: Florian Weimer <fweimer@redhat.com>

Date:   Fri Jun 23 22:51:00 2017 +0200

    inet_pton: Reject IPv6 addresses with many leading zeros [BZ #16637]

    2001:db8:00001::f is not a valid IPv6 address according to RFC 2373.

We do not want this behavioral change in Red Hat Enterprise Linux 7.

See rhbz#1484034 for some discussion.

diff --git a/resolv/inet_pton.c b/resolv/inet_pton.c

index 16ee33e0c0dfb015..b95da47c17ef8afc 100644

--- a/resolv/inet_pton.c

+++ b/resolv/inet_pton.c

@@ -144,8 +144,7 @@ inet_pton6 (const char *src, const char *src_endp, unsigned char *dst)

 {

   unsigned char tmp[NS_IN6ADDRSZ], *tp, *endp, *colonp;

   const char *curtok;

-  int ch;

-  size_t xdigits_seen;	/* Number of hex digits since colon.  */

+  int ch, saw_xdigit;

   unsigned int val;

   tp = memset (tmp, '\0', NS_IN6ADDRSZ);

@@ -163,7 +162,7 @@ inet_pton6 (const char *src, const char *src_endp, unsigned char *dst)

     }

   curtok = src;

-  xdigits_seen = 0;

+  saw_xdigit = 0;

   val = 0;

   while (src < src_endp)

     {

@@ -171,19 +170,17 @@ inet_pton6 (const char *src, const char *src_endp, unsigned char *dst)

       int digit = hex_digit_value (ch);

       if (digit >= 0)

 	{

-	  if (xdigits_seen == 4)

-	    return 0;

 	  val <<= 4;

 	  val |= digit;

 	  if (val > 0xffff)

 	    return 0;

-	  ++xdigits_seen;

+	  saw_xdigit = 1;

 	  continue;

 	}

       if (ch == ':')

 	{

 	  curtok = src;

-	  if (xdigits_seen == 0)

+	  if (!saw_xdigit)

 	    {

 	      if (colonp)

 		return 0;

@@ -196,7 +193,7 @@ inet_pton6 (const char *src, const char *src_endp, unsigned char *dst)

 	    return 0;

 	  *tp++ = (unsigned char) (val >> 8) & 0xff;

 	  *tp++ = (unsigned char) val & 0xff;

-	  xdigits_seen = 0;

+	  saw_xdigit = 0;

 	  val = 0;

 	  continue;

 	}

@@ -204,12 +201,12 @@ inet_pton6 (const char *src, const char *src_endp, unsigned char *dst)

           && inet_pton4 (curtok, src_endp, tp) > 0)

 	{

 	  tp += NS_INADDRSZ;

-	  xdigits_seen = 0;

+	  saw_xdigit = 0;

 	  break;  /* '\0' was seen by inet_pton4.  */

 	}

       return 0;

     }

-  if (xdigits_seen > 0)

+  if (saw_xdigit)

     {

       if (tp + NS_INT16SZ > endp)

 	return 0;

diff --git a/resolv/tst-inet_pton.c b/resolv/tst-inet_pton.c

index 4bb9f8119378b467..7fffb24cdf9eb1f4 100644

--- a/resolv/tst-inet_pton.c

+++ b/resolv/tst-inet_pton.c

@@ -226,7 +226,13 @@ const struct test_case test_cases[] =

     },

     {.input = "2", },

     {.input = "2.", },

-    {.input = "2001:db8:00001::f", },

+    {.input = "2001:db8:00001::f",

+     .ipv6_ok = true,

+     .ipv6_expected = {

+       0x20, 0x1, 0xd, 0xb8, 0x0, 0x1, 0x0, 0x0,

+       0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0xf

+     },

+    },

     {.input = "2001:db8:10000::f", },

     {.input = "2001:db8:1234:5678:abcd:ef01:2345:67",

      .ipv6_ok = true,

@@ -448,7 +454,13 @@ const struct test_case test_cases[] =

        0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0

      },

     },

-    {.input = "::00001", },

+    {.input = "::00001",

+     .ipv6_ok = true,

+     .ipv6_expected = {

+       0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,

+       0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x1

+     },

+    },

     {.input = "::1",

      .ipv6_ok = true,

      .ipv6_expected = {