krb5 commit: Fix xdr_bytes() strict-aliasing violations

[Greg Hudson]

https://github.com/krb5/krb5/commit/21b39d0196e3e0bb6b1bfbf5d60a0596cfc82e27
commit 21b39d0196e3e0bb6b1bfbf5d60a0596cfc82e27
Author: Greg Hudson <ghudson at mit.edu>
Date:   Tue Dec 10 12:06:05 2019 -0500

    Fix xdr_bytes() strict-aliasing violations
    
    When xdr_bytes() is used for a gss_buffer_desc object, a temporary
    character pointer must be used for the data value to avoid a strict
    aliasing violation.
    
    When xdr_bytes() is used for a krb5_keyblock object, a temporary
    character pointer must also be used, even though the data pointer is
    of type unsigned char *, to avoid a clang warning on macOS due to the
    "#pragma pack" declaration in krb5.h.

 src/lib/kadm5/kadm_rpc_xdr.c   |    8 +++++---
 src/lib/rpc/auth_gssapi_misc.c |   21 +++++++++++++--------
 src/lib/rpc/authgss_prot.c     |    5 ++++-
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/src/lib/kadm5/kadm_rpc_xdr.c b/src/lib/kadm5/kadm_rpc_xdr.c
index f22ea7f..8383e4e 100644
--- a/src/lib/kadm5/kadm_rpc_xdr.c
+++ b/src/lib/kadm5/kadm_rpc_xdr.c
@@ -1125,14 +1125,16 @@ xdr_krb5_salttype(XDR *xdrs, krb5_int32 *objp)
 bool_t
 xdr_krb5_keyblock(XDR *xdrs, krb5_keyblock *objp)
 {
+   char *cp;
+
    /* XXX This only works because free_keyblock assumes ->contents
       is allocated by malloc() */
-
    if(!xdr_krb5_enctype(xdrs, &objp->enctype))
       return FALSE;
-   if(!xdr_bytes(xdrs, (char **) &objp->contents, (unsigned int *)
-		 &objp->length, ~0))
+   cp = (char *)objp->contents;
+   if(!xdr_bytes(xdrs, &cp, &objp->length, ~0))
       return FALSE;
+   objp->contents = (uint8_t *)cp;
    return TRUE;
 }
 
diff --git a/src/lib/rpc/auth_gssapi_misc.c b/src/lib/rpc/auth_gssapi_misc.c
index a05ea19..a60eb7f 100644
--- a/src/lib/rpc/auth_gssapi_misc.c
+++ b/src/lib/rpc/auth_gssapi_misc.c
@@ -45,9 +45,11 @@ bool_t xdr_gss_buf(
      bool_t result;
      /* Fix type mismatches between APIs.  */
      unsigned int length = buf->length;
-     result = xdr_bytes(xdrs, (char **) &buf->value, &length,
+     char *cp = buf->value;
+     result = xdr_bytes(xdrs, &cp, &length,
 			(xdrs->x_op == XDR_DECODE && buf->value == NULL)
 			? (unsigned int) -1 : (unsigned int) buf->length);
+     buf->value = cp;
      buf->length = length;
      return result;
 }
@@ -204,6 +206,7 @@ bool_t auth_gssapi_wrap_data(
      XDR temp_xdrs;
      int conf_state;
      unsigned int length;
+     char *cp;
 
      PRINTF(("gssapi_wrap_data: starting\n"));
 
@@ -243,13 +246,13 @@ bool_t auth_gssapi_wrap_data(
 
      /* write the token */
      length = out_buf.length;
-     if (! xdr_bytes(out_xdrs, (char **) &out_buf.value,
-		     (unsigned int *) &length,
-		     out_buf.length)) {
+     cp = out_buf.value;
+     if (! xdr_bytes(out_xdrs, &cp, &length, out_buf.length)) {
 	  PRINTF(("gssapi_wrap_data: serializing encrypted data failed\n"));
 	  XDR_DESTROY(&temp_xdrs);
 	  return FALSE;
      }
+     out_buf.value = cp;
 
      *major = gss_release_buffer(minor, &out_buf);
 
@@ -272,6 +275,7 @@ bool_t auth_gssapi_unwrap_data(
      uint32_t verf_seq_num;
      int conf, qop;
      unsigned int length;
+     char *cp;
 
      PRINTF(("gssapi_unwrap_data: starting\n"));
 
@@ -280,14 +284,15 @@ bool_t auth_gssapi_unwrap_data(
 
      in_buf.value = NULL;
      out_buf.value = NULL;
-     if (! xdr_bytes(in_xdrs, (char **) &in_buf.value,
-		     &length, (unsigned int) -1)) {
+     cp = in_buf.value;
+     if (! xdr_bytes(in_xdrs, &cp, &length, (unsigned int) -1)) {
 	 PRINTF(("gssapi_unwrap_data: deserializing encrypted data failed\n"));
 	 temp_xdrs.x_op = XDR_FREE;
-	 (void)xdr_bytes(&temp_xdrs, (char **) &in_buf.value, &length,
-			 (unsigned int) -1);
+	 (void)xdr_bytes(&temp_xdrs, &cp, &length, (unsigned int) -1);
+	 in_buf.value = NULL;
 	 return FALSE;
      }
+     in_buf.value = cp;
      in_buf.length = length;
 
      *major = gss_unseal(minor, context, &in_buf, &out_buf, &conf,
diff --git a/src/lib/rpc/authgss_prot.c b/src/lib/rpc/authgss_prot.c
index a5a587f..9a48277 100644
--- a/src/lib/rpc/authgss_prot.c
+++ b/src/lib/rpc/authgss_prot.c
@@ -50,6 +50,7 @@ xdr_rpc_gss_buf(XDR *xdrs, gss_buffer_t buf, u_int maxsize)
 {
 	bool_t xdr_stat;
 	u_int tmplen;
+	char *cp;
 
 	if (xdrs->x_op != XDR_DECODE) {
 		if (buf->length > UINT_MAX)
@@ -57,7 +58,9 @@ xdr_rpc_gss_buf(XDR *xdrs, gss_buffer_t buf, u_int maxsize)
 		else
 			tmplen = buf->length;
 	}
-	xdr_stat = xdr_bytes(xdrs, (char **)&buf->value, &tmplen, maxsize);
+	cp = buf->value;
+	xdr_stat = xdr_bytes(xdrs, &cp, &tmplen, maxsize);
+	buf->value = cp;
 
 	if (xdr_stat && xdrs->x_op == XDR_DECODE)
 		buf->length = tmplen;