resolve: Remove __res_context_query alloca usage
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Commit Message
The bufsize on current Linux build is:
size_t bufsize = (type == 439963904 ? 2 : 1) * (12 + 4 + 255 + 1);
So with upper bound as 544 (2 * (12 + 4 + 255 + 1)). However, it might
increase to 2 * PACKETSIZE later with malloc. The default scratch_buffer
should fullfill the most usual allocation requirement.
Checked on x86_64-linux-gnu and i686-linux-gnu.
---
resolv/res_query.c | 47 +++++++++++++++++++++++-----------------------
1 file changed, 24 insertions(+), 23 deletions(-)
Comments
* Adhemerval Zanella:
> @@ -146,20 +150,20 @@ __res_context_query (struct resolv_context *ctx, const char *name,
> /* Align the buffer. */
> int npad = ((nquery1 + __alignof__ (HEADER) - 1)
> & ~(__alignof__ (HEADER) - 1)) - nquery1;
> - if (n > bufsize - npad)
> + if (n > buf.length - npad)
> {
> n = -1;
> goto unspec_nomem;
> }
> int nused = n + npad;
The alignment code shouldn't be necessary anymore.
Thanks,
Florian
On Thu, Sep 14, 2023 at 02:54:07PM -0300, Adhemerval Zanella wrote:
> The bufsize on current Linux build is:
>
> size_t bufsize = (type == 439963904 ? 2 : 1) * (12 + 4 + 255 + 1);
>
> So with upper bound as 544 (2 * (12 + 4 + 255 + 1)). However, it might
> increase to 2 * PACKETSIZE later with malloc. The default scratch_buffer
> should fullfill the most usual allocation requirement.
>
> Checked on x86_64-linux-gnu and i686-linux-gnu.
LGTM,
Reviewed-by: Joe Simmons-Talbott <josimmon@redhat.com>
> ---
> resolv/res_query.c | 47 +++++++++++++++++++++++-----------------------
> 1 file changed, 24 insertions(+), 23 deletions(-)
>
> diff --git a/resolv/res_query.c b/resolv/res_query.c
> index 049de91b95..b234db83c1 100644
> --- a/resolv/res_query.c
> +++ b/resolv/res_query.c
> @@ -80,6 +80,7 @@
> #include <stdlib.h>
> #include <string.h>
> #include <shlib-compat.h>
> +#include <scratch_buffer.h>
>
> #if PACKETSZ > 65536
> #define MAXPACKET PACKETSZ
> @@ -114,11 +115,14 @@ __res_context_query (struct resolv_context *ctx, const char *name,
> struct __res_state *statp = ctx->resp;
> UHEADER *hp = (UHEADER *) answer;
> UHEADER *hp2;
> - int n, use_malloc = 0;
> -
> - size_t bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * QUERYSIZE;
> - u_char *buf = alloca (bufsize);
> - u_char *query1 = buf;
> + int n;
> +
> + /* It requires 2 times QUERYSIZE for type == T_QUERY_A_AND_AAAA. */
> + struct scratch_buffer buf;
> + scratch_buffer_init (&buf);
> + _Static_assert (2 * QUERYSIZE <= sizeof (buf.__space.__c),
> + "scratch_buffer too small");
> + u_char *query1 = buf.data;
> int nquery1 = -1;
> u_char *query2 = NULL;
> int nquery2 = 0;
> @@ -129,14 +133,14 @@ __res_context_query (struct resolv_context *ctx, const char *name,
> if (type == T_QUERY_A_AND_AAAA)
> {
> n = __res_context_mkquery (ctx, QUERY, name, class, T_A, NULL,
> - query1, bufsize);
> + query1, buf.length);
> if (n > 0)
> {
> if ((statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
> {
> /* Use RESOLV_EDNS_BUFFER_SIZE because the receive
> buffer can be reallocated. */
> - n = __res_nopt (ctx, n, query1, bufsize,
> + n = __res_nopt (ctx, n, query1, buf.length,
> RESOLV_EDNS_BUFFER_SIZE);
> if (n < 0)
> goto unspec_nomem;
> @@ -146,20 +150,20 @@ __res_context_query (struct resolv_context *ctx, const char *name,
> /* Align the buffer. */
> int npad = ((nquery1 + __alignof__ (HEADER) - 1)
> & ~(__alignof__ (HEADER) - 1)) - nquery1;
> - if (n > bufsize - npad)
> + if (n > buf.length - npad)
> {
> n = -1;
> goto unspec_nomem;
> }
> int nused = n + npad;
> - query2 = buf + nused;
> + query2 = buf.data + nused;
> n = __res_context_mkquery (ctx, QUERY, name, class, T_AAAA,
> - NULL, query2, bufsize - nused);
> + NULL, query2, buf.length - nused);
> if (n > 0
> && (statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
> /* Use RESOLV_EDNS_BUFFER_SIZE because the receive
> buffer can be reallocated. */
> - n = __res_nopt (ctx, n, query2, bufsize,
> + n = __res_nopt (ctx, n, query2, buf.length,
> RESOLV_EDNS_BUFFER_SIZE);
> nquery2 = n;
> }
> @@ -169,7 +173,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
> else
> {
> n = __res_context_mkquery (ctx, QUERY, name, class, type, NULL,
> - query1, bufsize);
> + query1, buf.length);
>
> if (n > 0
> && (statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
> @@ -181,27 +185,25 @@ __res_context_query (struct resolv_context *ctx, const char *name,
> advertise = anslen;
> else
> advertise = RESOLV_EDNS_BUFFER_SIZE;
> - n = __res_nopt (ctx, n, query1, bufsize, advertise);
> + n = __res_nopt (ctx, n, query1, buf.length, advertise);
> }
>
> nquery1 = n;
> }
>
> - if (__glibc_unlikely (n <= 0) && !use_malloc) {
> + if (__glibc_unlikely (n <= 0)) {
> /* Retry just in case res_nmkquery failed because of too
> short buffer. Shouldn't happen. */
> - bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * MAXPACKET;
> - buf = malloc (bufsize);
> - if (buf != NULL) {
> - query1 = buf;
> - use_malloc = 1;
> + if (scratch_buffer_set_array_size (&buf,
> + T_QUERY_A_AND_AAAA ? 2 : 1,
> + MAXPACKET)) {
> + query1 = buf.data;
> goto again;
> }
> }
> if (__glibc_unlikely (n <= 0)) {
> RES_SET_H_ERRNO(statp, NO_RECOVERY);
> - if (use_malloc)
> - free (buf);
> + scratch_buffer_free (&buf);
> return (n);
> }
>
> @@ -224,8 +226,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
> answerp2_malloced);
> }
>
> - if (use_malloc)
> - free (buf);
> + scratch_buffer_free (&buf);
> if (n < 0) {
> RES_SET_H_ERRNO(statp, TRY_AGAIN);
> return (n);
> --
> 2.34.1
>
On 14/09/23 17:37, Florian Weimer wrote:
> * Adhemerval Zanella:
>
>> @@ -146,20 +150,20 @@ __res_context_query (struct resolv_context *ctx, const char *name,
>> /* Align the buffer. */
>> int npad = ((nquery1 + __alignof__ (HEADER) - 1)
>> & ~(__alignof__ (HEADER) - 1)) - nquery1;
>> - if (n > bufsize - npad)
>> + if (n > buf.length - npad)
>> {
>> n = -1;
>> goto unspec_nomem;
>> }
>> int nused = n + npad;
>
> The alignment code shouldn't be necessary anymore.
Indeed, I will update the patch.
@@ -80,6 +80,7 @@
#include <stdlib.h>
#include <string.h>
#include <shlib-compat.h>
+#include <scratch_buffer.h>
#if PACKETSZ > 65536
#define MAXPACKET PACKETSZ
@@ -114,11 +115,14 @@ __res_context_query (struct resolv_context *ctx, const char *name,
struct __res_state *statp = ctx->resp;
UHEADER *hp = (UHEADER *) answer;
UHEADER *hp2;
- int n, use_malloc = 0;
-
- size_t bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * QUERYSIZE;
- u_char *buf = alloca (bufsize);
- u_char *query1 = buf;
+ int n;
+
+ /* It requires 2 times QUERYSIZE for type == T_QUERY_A_AND_AAAA. */
+ struct scratch_buffer buf;
+ scratch_buffer_init (&buf);
+ _Static_assert (2 * QUERYSIZE <= sizeof (buf.__space.__c),
+ "scratch_buffer too small");
+ u_char *query1 = buf.data;
int nquery1 = -1;
u_char *query2 = NULL;
int nquery2 = 0;
@@ -129,14 +133,14 @@ __res_context_query (struct resolv_context *ctx, const char *name,
if (type == T_QUERY_A_AND_AAAA)
{
n = __res_context_mkquery (ctx, QUERY, name, class, T_A, NULL,
- query1, bufsize);
+ query1, buf.length);
if (n > 0)
{
if ((statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
{
/* Use RESOLV_EDNS_BUFFER_SIZE because the receive
buffer can be reallocated. */
- n = __res_nopt (ctx, n, query1, bufsize,
+ n = __res_nopt (ctx, n, query1, buf.length,
RESOLV_EDNS_BUFFER_SIZE);
if (n < 0)
goto unspec_nomem;
@@ -146,20 +150,20 @@ __res_context_query (struct resolv_context *ctx, const char *name,
/* Align the buffer. */
int npad = ((nquery1 + __alignof__ (HEADER) - 1)
& ~(__alignof__ (HEADER) - 1)) - nquery1;
- if (n > bufsize - npad)
+ if (n > buf.length - npad)
{
n = -1;
goto unspec_nomem;
}
int nused = n + npad;
- query2 = buf + nused;
+ query2 = buf.data + nused;
n = __res_context_mkquery (ctx, QUERY, name, class, T_AAAA,
- NULL, query2, bufsize - nused);
+ NULL, query2, buf.length - nused);
if (n > 0
&& (statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
/* Use RESOLV_EDNS_BUFFER_SIZE because the receive
buffer can be reallocated. */
- n = __res_nopt (ctx, n, query2, bufsize,
+ n = __res_nopt (ctx, n, query2, buf.length,
RESOLV_EDNS_BUFFER_SIZE);
nquery2 = n;
}
@@ -169,7 +173,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
else
{
n = __res_context_mkquery (ctx, QUERY, name, class, type, NULL,
- query1, bufsize);
+ query1, buf.length);
if (n > 0
&& (statp->options & (RES_USE_EDNS0|RES_USE_DNSSEC)) != 0)
@@ -181,27 +185,25 @@ __res_context_query (struct resolv_context *ctx, const char *name,
advertise = anslen;
else
advertise = RESOLV_EDNS_BUFFER_SIZE;
- n = __res_nopt (ctx, n, query1, bufsize, advertise);
+ n = __res_nopt (ctx, n, query1, buf.length, advertise);
}
nquery1 = n;
}
- if (__glibc_unlikely (n <= 0) && !use_malloc) {
+ if (__glibc_unlikely (n <= 0)) {
/* Retry just in case res_nmkquery failed because of too
short buffer. Shouldn't happen. */
- bufsize = (type == T_QUERY_A_AND_AAAA ? 2 : 1) * MAXPACKET;
- buf = malloc (bufsize);
- if (buf != NULL) {
- query1 = buf;
- use_malloc = 1;
+ if (scratch_buffer_set_array_size (&buf,
+ T_QUERY_A_AND_AAAA ? 2 : 1,
+ MAXPACKET)) {
+ query1 = buf.data;
goto again;
}
}
if (__glibc_unlikely (n <= 0)) {
RES_SET_H_ERRNO(statp, NO_RECOVERY);
- if (use_malloc)
- free (buf);
+ scratch_buffer_free (&buf);
return (n);
}
@@ -224,8 +226,7 @@ __res_context_query (struct resolv_context *ctx, const char *name,
answerp2_malloced);
}
- if (use_malloc)
- free (buf);
+ scratch_buffer_free (&buf);
if (n < 0) {
RES_SET_H_ERRNO(statp, TRY_AGAIN);
return (n);