resolv: Fix unaligned accesses to fields in HEADER struct

The structure HEADER is normally aligned to a word boundary but
sometimes it needs to be accessed when aligned on a byte boundary.
This change defines a new typedef, UHEADER, with alignment 1.
It is used to ensure the fields are accessed with byte loads and
stores when necessary.

V4: Change to res_mkquery.c deleted.  Small whitespace fix.

V5: Move UHEADER typedef to resolv/resolv-internal.h.  Replace all
HEADER usage with UHEADER in resolv/res_send.c.

Signed-off-by: John David Anglin <dave.anglin@bell.net>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/resolv/resolv-internal.h b/resolv/resolv-internal.h
index 2fa57d394f..9d2e832d68 100644
--- a/resolv/resolv-internal.h
+++ b/resolv/resolv-internal.h
@@ -27,6 +27,13 @@
 #define RES_F_CONN      0x00000002 /* Socket is connected.  */
 #define RES_F_EDNS0ERR  0x00000004 /* EDNS0 caused errors.  */
 
+/* The structure HEADER is normally aligned on a word boundary.  In
+   some code, we need to access this structure when it may be aligned
+   on a byte boundary.  To avoid unaligned accesses, we need a typedef
+   with alignment one.  This ensures the fields are accessed with byte
+   loads and stores.  */
+typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
+
 /* Legacy function.  This needs to be removed once all NSS modules
    have been adjusted.  */
 static inline bool