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resolv: Fix unaligned accesses to fields in HEADER struct

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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>
This commit is contained in:
John David Anglin 2022-03-22 17:35:54 +00:00
parent bc0d18d873
commit 05dec22d7b
3 changed files with 21 additions and 14 deletions
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10
resolv/res_query.c
View file

@ -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;

18
resolv/res_send.c
View file

@ -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,

7
resolv/resolv-internal.h
View file

@ -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