* [PATCH v4] Fix misaligned accesses to fields in HEADER struct defined in <arpa/nameser_compat.h>
@ 2022-03-17 23:04 John David Anglin
2022-03-18 17:37 ` Adhemerval Zanella
0 siblings, 1 reply; 2+ messages in thread
From: John David Anglin @ 2022-03-17 23:04 UTC (permalink / raw)
To: libc-alpha
[-- Attachment #1: Type: text/plain, Size: 3272 bytes --]
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.
Dave
---
diff --git a/resolv/res_query.c b/resolv/res_query.c
index 5d0a68dc81..4ac2c516a1 100644
--- a/resolv/res_query.c
+++ b/resolv/res_query.c
@@ -81,6 +81,14 @@
#include <string.h>
#include <shlib-compat.h>
+/* The structure HEADER is normally aligned to a word boundary and its
+ fields are accessed using word loads and stores. We need to access
+ this structure when it is aligned on a byte boundary. This can cause
+ problems on machines with strict alignment. So, we create a new
+ typedef to reduce its alignment to one. This ensures the fields are
+ accessed with byte loads and stores. */
+typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
+
#if PACKETSZ > 65536
#define MAXPACKET PACKETSZ
#else
@@ -112,8 +120,8 @@ __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 +225,7 @@ __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 +236,7 @@ __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 +346,7 @@ __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 5d6be4b82d..24e98f0bfe 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -111,6 +111,15 @@
#include <libc-diag.h>
#include <random-bits.h>
+/* The structure HEADER is normally aligned to a word boundary and its
+ fields are accessed using word loads and stores. We need to access
+ this structure when it is aligned on a byte boundary. This can cause
+ problems on machines with strict alignment. So, we create a new
+ typedef to reduce its alignment to one. This ensures the fields are
+ accessed with byte loads and stores. */
+typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
+#define HEADER UHEADER
+
#if PACKETSZ > 65536
#define MAXPACKET PACKETSZ
#else
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^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH v4] Fix misaligned accesses to fields in HEADER struct defined in <arpa/nameser_compat.h>
2022-03-17 23:04 [PATCH v4] Fix misaligned accesses to fields in HEADER struct defined in <arpa/nameser_compat.h> John David Anglin
@ 2022-03-18 17:37 ` Adhemerval Zanella
0 siblings, 0 replies; 2+ messages in thread
From: Adhemerval Zanella @ 2022-03-18 17:37 UTC (permalink / raw)
To: John David Anglin, libc-alpha
On 17/03/2022 20:04, John David Anglin wrote:
> 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.
>
> Dave
> ---
>
> diff --git a/resolv/res_query.c b/resolv/res_query.c
> index 5d0a68dc81..4ac2c516a1 100644
> --- a/resolv/res_query.c
> +++ b/resolv/res_query.c
> @@ -81,6 +81,14 @@
> #include <string.h>
> #include <shlib-compat.h>
>
> +/* The structure HEADER is normally aligned to a word boundary and its
> + fields are accessed using word loads and stores. We need to access
> + this structure when it is aligned on a byte boundary. This can cause
> + problems on machines with strict alignment. So, we create a new
> + typedef to reduce its alignment to one. This ensures the fields are
> + accessed with byte loads and stores. */
> +typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
> +
Instead of replicate it on both files, I think a better strategy would to
move it to resolv/resolv-internal.h.
> #if PACKETSZ > 65536
> #define MAXPACKET PACKETSZ
> #else
> @@ -112,8 +120,8 @@ __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 +225,7 @@ __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 +236,7 @@ __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 +346,7 @@ __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 5d6be4b82d..24e98f0bfe 100644
> --- a/resolv/res_send.c
> +++ b/resolv/res_send.c
> @@ -111,6 +111,15 @@
> #include <libc-diag.h>
> #include <random-bits.h>
>
> +/* The structure HEADER is normally aligned to a word boundary and its
> + fields are accessed using word loads and stores. We need to access
> + this structure when it is aligned on a byte boundary. This can cause
> + problems on machines with strict alignment. So, we create a new
> + typedef to reduce its alignment to one. This ensures the fields are
> + accessed with byte loads and stores. */
> +typedef HEADER __attribute__ ((__aligned__(1))) UHEADER;
> +#define HEADER UHEADER
> +
I think it would be better to just do what you did on res_query.c and
replace all required HEADER usage with UHEADER.
> #if PACKETSZ > 65536
> #define MAXPACKET PACKETSZ
> #else
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