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

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

[Ludwig Rydberg]

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>
---
 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 e9316b3c3772..a46a92432b50 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 ba1c1d0c0cf6..37db01a1b048 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;
 

base-commit: b3bee76c5f59498b9c189608f0a3132e2013fa1a
-- 
2.35.3

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

[Florian Weimer]

* Ludwig Rydberg:

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

Looks reasonable to me.  I will do some tests (although not on
strict-alignment targets, admittedly) and install it.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian