[glibc] resolv: Fix a few unaligned accesses to fields in HEADER

[glibc] resolv: Fix a few unaligned accesses to fields in HEADER

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=fc039ce8502d236f11074eb58468be24b4fa8cc7

commit fc039ce8502d236f11074eb58468be24b4fa8cc7
Author: Ludwig Rydberg <ludwig.rydberg@gaisler.com>
Date:   Mon Dec 11 13:50:41 2023 +0100

    resolv: Fix a few unaligned accesses to fields in HEADER
    
    After refactoring the alloca usage in 40c0add7d4 ("resolve: Remove
    __res_context_query alloca usage") a few unaligned accesses to HEADER
    fields surfaced. These unaligned accesses led to problems when running
    the resolv test suite on sparc32-linux (leon) as many tests failed due to
    SIGBUS crashes.
    
    The issue(s) occured during T_QUERY_A_AND_AAAA queries as the second query
    now can start on an unaligned address (previously it was explicitly aligned).
    
    With this patch the unaligned accesses are now fixed by using the
    UHEADER instead to ensure the fields are accessed with byte
    loads/stores.
    
    The patch has been verfied by running the resolv test suite on sparc32
    and x86_64.
    
    Signed-off-by: Ludwig Rydberg <ludwig.rydberg@gaisler.com>
    Signed-off-by: Andreas Larsson <andreas@gaisler.com>
    Reviewed-by: Florian Weimer <fweimer@redhat.com>

Diff:
---
 resolv/res_mkquery.c      | 6 +++---
 resolv/res_queriesmatch.c | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/resolv/res_mkquery.c b/resolv/res_mkquery.c
index e9316b3c37..a46a92432b 100644
--- a/resolv/res_mkquery.c
+++ b/resolv/res_mkquery.c
@@ -100,7 +100,7 @@ __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
                        int class, int type, const unsigned char *data,
                        unsigned char *buf, int buflen)
 {
-  HEADER *hp;
+  UHEADER *hp;
   unsigned char *cp;
   int n;
   unsigned char *dnptrs[20], **dpp, **lastdnptr;
@@ -112,7 +112,7 @@ __res_context_mkquery (struct resolv_context *ctx, int op, const char *dname,
   if ((buf == NULL) || (buflen < HFIXEDSZ))
     return -1;
   memset (buf, 0, HFIXEDSZ);
-  hp = (HEADER *) buf;
+  hp = (UHEADER *) buf;
   /* We randomize the IDs every time.  The old code just incremented
      by one after the initial randomization which still predictable if
      the application does multiple requests.  */
@@ -250,7 +250,7 @@ __res_nopt (struct resolv_context *ctx,
             int n0, unsigned char *buf, int buflen, int anslen)
 {
   uint16_t flags = 0;
-  HEADER *hp = (HEADER *) buf;
+  UHEADER *hp = (UHEADER *) buf;
   unsigned char *cp = buf + n0;
   unsigned char *ep = buf + buflen;
 
diff --git a/resolv/res_queriesmatch.c b/resolv/res_queriesmatch.c
index ba1c1d0c0c..37db01a1b0 100644
--- a/resolv/res_queriesmatch.c
+++ b/resolv/res_queriesmatch.c
@@ -95,14 +95,14 @@ __libc_res_queriesmatch (const unsigned char *buf1, const unsigned char *eom1,
 
   /* Only header section present in replies to dynamic update
      packets.  */
-  if ((((HEADER *) buf1)->opcode == ns_o_update) &&
-      (((HEADER *) buf2)->opcode == ns_o_update))
+  if ((((UHEADER *) buf1)->opcode == ns_o_update) &&
+      (((UHEADER *) buf2)->opcode == ns_o_update))
     return 1;
 
   /* Note that we initially do not convert QDCOUNT to the host byte
      order.  We can compare it with the second buffer's QDCOUNT
      value without doing this.  */
-  int qdcount = ((HEADER *) buf1)->qdcount;
+  int qdcount = ((UHEADER *) buf1)->qdcount;
   if (qdcount != ((UHEADER *) buf2)->qdcount)
     return 0;