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>

diff --git a/resolv/res_query.c b/resolv/res_query.c
index 5d0a68dc81fdd8c7545780af6b983fb9fab31e51..3b5c60426143fb9a503b1fc1497ecdb7f7d4dac4 100644 (file)
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -112,8 +112,8 @@ __res_context_query (struct resolv_context *ctx, const char *name,
                     int *nanswerp2, int *resplen2, int *answerp2_malloced)
 {
        struct __res_state *statp = ctx->resp;
-       HEADER *hp = (HEADER *) answer;
-       HEADER *hp2;
+       UHEADER *hp = (UHEADER *) answer;
+       UHEADER *hp2;
        int n, use_malloc = 0;
 
        size_t bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * QUERYSIZE;
@@ -217,7 +217,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
 
        if (answerp != NULL)
          /* __res_context_send might have reallocated the buffer.  */
-         hp = (HEADER *) *answerp;
+         hp = (UHEADER *) *answerp;
 
        /* We simplify the following tests by assigning HP to HP2 or
           vice versa.  It is easy to verify that this is the same as
@@ -228,7 +228,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
          }
        else
          {
-           hp2 = (HEADER *) *answerp2;
+           hp2 = (UHEADER *) *answerp2;
            if (n < (int) sizeof (HEADER))
              {
                hp = hp2;
@@ -338,7 +338,7 @@ __res_context_search (struct resolv_context *ctx,
 {
        struct __res_state *statp = ctx->resp;
        const char *cp;
-       HEADER *hp = (HEADER *) answer;
+       UHEADER *hp = (UHEADER *) answer;
        char tmp[NS_MAXDNAME];
        u_int dots;
        int trailing_dot, ret, saved_herrno;

diff --git a/resolv/res_send.c b/resolv/res_send.c
index 5d6be4b82d383dc0ebdf22ebb52caff81b1ab172..d6c85fd7a2995dd1dbb8d1979e7ed4304f5fcc2d 100644 (file)
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -245,7 +245,7 @@ static void
 mask_ad_bit (struct resolv_context *ctx, void *buf)
 {
   if (!(ctx->resp->options & RES_TRUSTAD))
-    ((HEADER *) buf)->ad = 0;
+    ((UHEADER *) buf)->ad = 0;
 }
 
 int
@@ -560,9 +560,9 @@ send_vc(res_state statp,
        int *terrno, int ns, u_char **anscp, u_char **ansp2, int *anssizp2,
        int *resplen2, int *ansp2_malloced)
 {
-       const HEADER *hp = (HEADER *) buf;
-       const HEADER *hp2 = (HEADER *) buf2;
-       HEADER *anhp = (HEADER *) *ansp;
+       const UHEADER *hp = (UHEADER *) buf;
+       const UHEADER *hp2 = (UHEADER *) buf2;
+       UHEADER *anhp = (UHEADER *) *ansp;
        struct sockaddr *nsap = __res_get_nsaddr (statp, ns);
        int truncating, connreset, n;
        /* On some architectures compiler might emit a warning indicating
@@ -697,7 +697,7 @@ send_vc(res_state statp,
                thisansp = ansp2;
                thisresplenp = resplen2;
        }
-       anhp = (HEADER *) *thisansp;
+       anhp = (UHEADER *) *thisansp;
 
        *thisresplenp = rlen;
        /* Is the answer buffer too small?  */
@@ -718,7 +718,7 @@ send_vc(res_state statp,
                        *thisansp = newp;
                        if (thisansp == ansp2)
                          *ansp2_malloced = 1;
-                       anhp = (HEADER *) newp;
+                       anhp = (UHEADER *) newp;
                        /* A uint16_t can't be larger than MAXPACKET
                           thus it's safe to allocate MAXPACKET but
                           read RLEN bytes instead.  */
@@ -925,8 +925,8 @@ send_dg(res_state statp,
        int *terrno, int ns, int *v_circuit, int *gotsomewhere, u_char **anscp,
        u_char **ansp2, int *anssizp2, int *resplen2, int *ansp2_malloced)
 {
-       const HEADER *hp = (HEADER *) buf;
-       const HEADER *hp2 = (HEADER *) buf2;
+       const UHEADER *hp = (UHEADER *) buf;
+       const UHEADER *hp2 = (UHEADER *) buf2;
        struct timespec now, timeout, finish;
        struct pollfd pfd[1];
        int ptimeout;
@@ -1168,7 +1168,7 @@ send_dg(res_state statp,
                   MSG_TRUNC which is only available on Linux.  We
                   can abstract out the Linux-specific feature in the
                   future to detect truncation.  */
-               HEADER *anhp = (HEADER *) *thisansp;
+               UHEADER *anhp = (UHEADER *) *thisansp;
                socklen_t fromlen = sizeof(struct sockaddr_in6);
                assert (sizeof(from) <= fromlen);
                *thisresplenp = __recvfrom (pfd[0].fd, (char *) *thisansp,

diff --git a/resolv/resolv-internal.h b/resolv/resolv-internal.h
index 2fa57d394f70bcad372074401ad43c42bc4c6776..9d2e832d6839faf064b6a292a96784d00f22b938 100644 (file)
--- 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