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glibc/SOURCES/glibc-rh2129005.patch

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commit 1d495912a746e2a1ffb780c9a81fd234ec2464e8
Author: Florian Weimer <fweimer@redhat.com>
Date: Tue Aug 30 10:02:49 2022 +0200
nss_dns: Rewrite _nss_dns_gethostbyname4_r using current interfaces
Introduce struct alloc_buffer to this function, and use it and
struct ns_rr_cursor in gaih_getanswer_slice. Adjust gaih_getanswer
and gaih_getanswer_noaaaa accordingly.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index 1cb3be71f04d98eb..36789965c06757d0 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -101,13 +101,6 @@
#endif
#define MAXHOSTNAMELEN 256
-/* We need this time later. */
-typedef union querybuf
-{
- HEADER hdr;
- u_char buf[MAXPACKET];
-} querybuf;
-
/* For historic reasons, pointers to IP addresses are char *, so use a
single list type for addresses and host names. */
#define DYNARRAY_STRUCT ptrlist
@@ -126,18 +119,18 @@ static enum nss_status getanswer_ptr (unsigned char *packet, size_t packetlen,
char **hnamep, int *errnop,
int *h_errnop, int32_t *ttlp);
-static enum nss_status gaih_getanswer (const querybuf *answer1, int anslen1,
- const querybuf *answer2, int anslen2,
- const char *qname,
+static enum nss_status gaih_getanswer (unsigned char *packet1,
+ size_t packet1len,
+ unsigned char *packet2,
+ size_t packet2len,
+ struct alloc_buffer *abuf,
struct gaih_addrtuple **pat,
- char *buffer, size_t buflen,
int *errnop, int *h_errnop,
int32_t *ttlp);
-static enum nss_status gaih_getanswer_noaaaa (const querybuf *answer1,
- int anslen1,
- const char *qname,
+static enum nss_status gaih_getanswer_noaaaa (unsigned char *packet,
+ size_t packetlen,
+ struct alloc_buffer *abuf,
struct gaih_addrtuple **pat,
- char *buffer, size_t buflen,
int *errnop, int *h_errnop,
int32_t *ttlp);
@@ -409,17 +402,13 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
name = cp;
}
- union
- {
- querybuf *buf;
- u_char *ptr;
- } host_buffer;
- querybuf *orig_host_buffer;
- host_buffer.buf = orig_host_buffer = (querybuf *) alloca (2048);
+ unsigned char dns_packet_buffer[2048];
+ unsigned char *alt_dns_packet_buffer = dns_packet_buffer;
u_char *ans2p = NULL;
int nans2p = 0;
int resplen2 = 0;
int ans2p_malloced = 0;
+ struct alloc_buffer abuf = alloc_buffer_create (buffer, buflen);
int olderr = errno;
@@ -428,22 +417,21 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
if ((ctx->resp->options & RES_NOAAAA) == 0)
{
n = __res_context_search (ctx, name, C_IN, T_QUERY_A_AND_AAAA,
- host_buffer.buf->buf, 2048, &host_buffer.ptr,
- &ans2p, &nans2p, &resplen2, &ans2p_malloced);
+ dns_packet_buffer, sizeof (dns_packet_buffer),
+ &alt_dns_packet_buffer, &ans2p, &nans2p,
+ &resplen2, &ans2p_malloced);
if (n >= 0)
- status = gaih_getanswer (host_buffer.buf, n, (const querybuf *) ans2p,
- resplen2, name, pat, buffer, buflen,
- errnop, herrnop, ttlp);
+ status = gaih_getanswer (alt_dns_packet_buffer, n, ans2p, resplen2,
+ &abuf, pat, errnop, herrnop, ttlp);
}
else
{
n = __res_context_search (ctx, name, C_IN, T_A,
- host_buffer.buf->buf, 2048, NULL,
- NULL, NULL, NULL, NULL);
+ dns_packet_buffer, sizeof (dns_packet_buffer),
+ NULL, NULL, NULL, NULL, NULL);
if (n >= 0)
- status = gaih_getanswer_noaaaa (host_buffer.buf, n,
- name, pat, buffer, buflen,
- errnop, herrnop, ttlp);
+ status = gaih_getanswer_noaaaa (alt_dns_packet_buffer, n,
+ &abuf, pat, errnop, herrnop, ttlp);
}
if (n < 0)
{
@@ -474,12 +462,20 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
__set_errno (olderr);
}
+ /* Implement the buffer resizing protocol. */
+ if (alloc_buffer_has_failed (&abuf))
+ {
+ *errnop = ERANGE;
+ *herrnop = NETDB_INTERNAL;
+ status = NSS_STATUS_TRYAGAIN;
+ }
+
/* Check whether ans2p was separately allocated. */
if (ans2p_malloced)
free (ans2p);
- if (host_buffer.buf != orig_host_buffer)
- free (host_buffer.buf);
+ if (alt_dns_packet_buffer != dns_packet_buffer)
+ free (alt_dns_packet_buffer);
__resolv_context_put (ctx);
return status;
@@ -893,259 +889,152 @@ getanswer_ptr (unsigned char *packet, size_t packetlen,
return NSS_STATUS_TRYAGAIN;
}
+/* Parses DNS data found in PACKETLEN bytes at PACKET in struct
+ gaih_addrtuple address tuples. The new address tuples are linked
+ from **TAILP, with backing store allocated from ABUF, and *TAILP is
+ updated to point where the next tuple pointer should be stored. If
+ TTLP is not null, *TTLP is updated to reflect the minimum TTL. If
+ STORE_CANON is true, the canonical name is stored as part of the
+ first address tuple being written. */
static enum nss_status
-gaih_getanswer_slice (const querybuf *answer, int anslen, const char *qname,
- struct gaih_addrtuple ***patp,
- char **bufferp, size_t *buflenp,
- int *errnop, int *h_errnop, int32_t *ttlp, int *firstp)
+gaih_getanswer_slice (unsigned char *packet, size_t packetlen,
+ struct alloc_buffer *abuf,
+ struct gaih_addrtuple ***tailp,
+ int *errnop, int *h_errnop, int32_t *ttlp,
+ bool store_canon)
{
- char *buffer = *bufferp;
- size_t buflen = *buflenp;
-
- struct gaih_addrtuple **pat = *patp;
- const HEADER *hp = &answer->hdr;
- int ancount = ntohs (hp->ancount);
- int qdcount = ntohs (hp->qdcount);
- const u_char *cp = answer->buf + HFIXEDSZ;
- const u_char *end_of_message = answer->buf + anslen;
- if (__glibc_unlikely (qdcount != 1))
- {
- *h_errnop = NO_RECOVERY;
- return NSS_STATUS_UNAVAIL;
- }
-
- u_char packtmp[NS_MAXCDNAME];
- int n = __ns_name_unpack (answer->buf, end_of_message, cp,
- packtmp, sizeof packtmp);
- /* We unpack the name to check it for validity. But we do not need
- it later. */
- if (n != -1 && __ns_name_ntop (packtmp, buffer, buflen) == -1)
- {
- if (__glibc_unlikely (errno == EMSGSIZE))
- {
- too_small:
- *errnop = ERANGE;
- *h_errnop = NETDB_INTERNAL;
- return NSS_STATUS_TRYAGAIN;
- }
-
- n = -1;
- }
-
- if (__glibc_unlikely (n < 0))
- {
- *errnop = errno;
- *h_errnop = NO_RECOVERY;
- return NSS_STATUS_UNAVAIL;
- }
- if (__glibc_unlikely (__libc_res_hnok (buffer) == 0))
+ struct ns_rr_cursor c;
+ if (!__ns_rr_cursor_init (&c, packet, packetlen))
{
- errno = EBADMSG;
- *errnop = EBADMSG;
+ /* This should not happen because __res_context_query already
+ perfroms response validation. */
*h_errnop = NO_RECOVERY;
return NSS_STATUS_UNAVAIL;
}
- cp += n + QFIXEDSZ;
+ bool haveanswer = false; /* Set to true if at least one address. */
+ uint16_t qtype = ns_rr_cursor_qtype (&c);
+ int ancount = ns_rr_cursor_ancount (&c);
+ const unsigned char *expected_name = ns_rr_cursor_qname (&c);
+ /* expected_name may be updated to point into this buffer. */
+ unsigned char name_buffer[NS_MAXCDNAME];
- int haveanswer = 0;
- int had_error = 0;
- char *canon = NULL;
- char *h_name = NULL;
- int h_namelen = 0;
+ /* This is a pointer to a possibly-compressed name in the packet.
+ Eventually it is equivalent to the canonical name. If needed, it
+ is uncompressed and translated to text form when the first
+ address tuple is encountered. */
+ const unsigned char *compressed_alias_name = expected_name;
- if (ancount == 0)
+ if (ancount == 0 || !__res_binary_hnok (compressed_alias_name))
{
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
}
- while (ancount-- > 0 && cp < end_of_message && had_error == 0)
+ for (; ancount > -0; --ancount)
{
- n = __ns_name_unpack (answer->buf, end_of_message, cp,
- packtmp, sizeof packtmp);
- if (n != -1 &&
- (h_namelen = __ns_name_ntop (packtmp, buffer, buflen)) == -1)
- {
- if (__glibc_unlikely (errno == EMSGSIZE))
- goto too_small;
-
- n = -1;
- }
- if (__glibc_unlikely (n < 0))
- {
- ++had_error;
- continue;
- }
- if (*firstp && canon == NULL && __libc_res_hnok (buffer))
- {
- h_name = buffer;
- buffer += h_namelen;
- buflen -= h_namelen;
- }
-
- cp += n; /* name */
-
- if (__glibc_unlikely (cp + 10 > end_of_message))
- {
- ++had_error;
- continue;
- }
-
- uint16_t type;
- NS_GET16 (type, cp);
- uint16_t class;
- NS_GET16 (class, cp);
- int32_t ttl;
- NS_GET32 (ttl, cp);
- NS_GET16 (n, cp); /* RDATA length. */
-
- if (end_of_message - cp < n)
+ struct ns_rr_wire rr;
+ if (!__ns_rr_cursor_next (&c, &rr))
{
- /* RDATA extends beyond the end of the packet. */
- ++had_error;
- continue;
+ *h_errnop = NO_RECOVERY;
+ return NSS_STATUS_UNAVAIL;
}
- if (class != C_IN)
- {
- cp += n;
- continue;
- }
+ /* Update TTL for known record types. */
+ if ((rr.rtype == T_CNAME || rr.rtype == qtype)
+ && ttlp != NULL && *ttlp > rr.ttl)
+ *ttlp = rr.ttl;
- if (type == T_CNAME)
+ if (rr.rtype == T_CNAME)
{
- char tbuf[MAXDNAME];
-
- /* A CNAME could also have a TTL entry. */
- if (ttlp != NULL && ttl < *ttlp)
- *ttlp = ttl;
-
- n = __libc_dn_expand (answer->buf, end_of_message, cp,
- tbuf, sizeof tbuf);
- if (__glibc_unlikely (n < 0))
- {
- ++had_error;
- continue;
- }
- cp += n;
-
- if (*firstp && __libc_res_hnok (tbuf))
+ /* NB: No check for owner name match, based on historic
+ precedent. Record the CNAME target as the new expected
+ name. */
+ int n = __ns_name_unpack (c.begin, c.end, rr.rdata,
+ name_buffer, sizeof (name_buffer));
+ if (n < 0)
{
- /* Reclaim buffer space. */
- if (h_name + h_namelen == buffer)
- {
- buffer = h_name;
- buflen += h_namelen;
- }
-
- n = strlen (tbuf) + 1;
- if (__glibc_unlikely (n > buflen))
- goto too_small;
- if (__glibc_unlikely (n >= MAXHOSTNAMELEN))
- {
- ++had_error;
- continue;
- }
-
- canon = buffer;
- buffer = __mempcpy (buffer, tbuf, n);
- buflen -= n;
- h_namelen = 0;
+ *h_errnop = NO_RECOVERY;
+ return NSS_STATUS_UNAVAIL;
}
- continue;
+ expected_name = name_buffer;
+ if (store_canon && __res_binary_hnok (name_buffer))
+ /* This name can be used as a canonical name. Do not
+ translate to text form here to conserve buffer space.
+ Point to the compressed name because name_buffer can be
+ overwritten with an unusable name later. */
+ compressed_alias_name = rr.rdata;
}
-
- /* Stop parsing if we encounter a record with incorrect RDATA
- length. */
- if (type == T_A || type == T_AAAA)
+ else if (rr.rtype == qtype
+ && __ns_samebinaryname (rr.rname, expected_name)
+ && rr.rdlength == rrtype_to_rdata_length (qtype))
{
- if (n != rrtype_to_rdata_length (type))
+ struct gaih_addrtuple *ntup
+ = alloc_buffer_alloc (abuf, struct gaih_addrtuple);
+ /* Delay error reporting to the callers (they implement the
+ ERANGE buffer resizing handshake). */
+ if (ntup != NULL)
{
- ++had_error;
- continue;
+ ntup->next = NULL;
+ if (store_canon && compressed_alias_name != NULL)
+ {
+ /* This assumes that all the CNAME records come
+ first. Use MAXHOSTNAMELEN instead of
+ NS_MAXCDNAME for additional length checking.
+ However, these checks are not expected to fail
+ because all size NS_MAXCDNAME names should into
+ the hname buffer because no escaping is
+ needed. */
+ char unsigned nbuf[NS_MAXCDNAME];
+ char hname[MAXHOSTNAMELEN + 1];
+ if (__ns_name_unpack (c.begin, c.end,
+ compressed_alias_name,
+ nbuf, sizeof (nbuf)) >= 0
+ && __ns_name_ntop (nbuf, hname, sizeof (hname)) >= 0)
+ /* Space checking is performed by the callers. */
+ ntup->name = alloc_buffer_copy_string (abuf, hname);
+ store_canon = false;
+ }
+ else
+ ntup->name = NULL;
+ if (rr.rdlength == 4)
+ ntup->family = AF_INET;
+ else
+ ntup->family = AF_INET6;
+ memcpy (ntup->addr, rr.rdata, rr.rdlength);
+ ntup->scopeid = 0;
+
+ /* Link in the new tuple, and update the tail pointer to
+ point to its next field. */
+ **tailp = ntup;
+ *tailp = &ntup->next;
+
+ haveanswer = true;
}
}
- else
- {
- /* Skip unknown records. */
- cp += n;
- continue;
- }
-
- assert (type == T_A || type == T_AAAA);
- if (*pat == NULL)
- {
- uintptr_t pad = (-(uintptr_t) buffer
- % __alignof__ (struct gaih_addrtuple));
- buffer += pad;
- buflen = buflen > pad ? buflen - pad : 0;
-
- if (__glibc_unlikely (buflen < sizeof (struct gaih_addrtuple)))
- goto too_small;
-
- *pat = (struct gaih_addrtuple *) buffer;
- buffer += sizeof (struct gaih_addrtuple);
- buflen -= sizeof (struct gaih_addrtuple);
- }
-
- (*pat)->name = NULL;
- (*pat)->next = NULL;
-
- if (*firstp)
- {
- /* We compose a single hostent out of the entire chain of
- entries, so the TTL of the hostent is essentially the lowest
- TTL in the chain. */
- if (ttlp != NULL && ttl < *ttlp)
- *ttlp = ttl;
-
- (*pat)->name = canon ?: h_name;
-
- *firstp = 0;
- }
-
- (*pat)->family = type == T_A ? AF_INET : AF_INET6;
- memcpy ((*pat)->addr, cp, n);
- cp += n;
- (*pat)->scopeid = 0;
-
- pat = &((*pat)->next);
-
- haveanswer = 1;
}
if (haveanswer)
{
- *patp = pat;
- *bufferp = buffer;
- *buflenp = buflen;
-
*h_errnop = NETDB_SUCCESS;
return NSS_STATUS_SUCCESS;
}
-
- /* Special case here: if the resolver sent a result but it only
- contains a CNAME while we are looking for a T_A or T_AAAA record,
- we fail with NOTFOUND instead of TRYAGAIN. */
- if (canon != NULL)
+ else
{
+ /* Special case here: if the resolver sent a result but it only
+ contains a CNAME while we are looking for a T_A or T_AAAA
+ record, we fail with NOTFOUND. */
*h_errnop = HOST_NOT_FOUND;
return NSS_STATUS_NOTFOUND;
}
-
- *h_errnop = NETDB_INTERNAL;
- return NSS_STATUS_TRYAGAIN;
}
static enum nss_status
-gaih_getanswer (const querybuf *answer1, int anslen1, const querybuf *answer2,
- int anslen2, const char *qname,
- struct gaih_addrtuple **pat, char *buffer, size_t buflen,
+gaih_getanswer (unsigned char *packet1, size_t packet1len,
+ unsigned char *packet2, size_t packet2len,
+ struct alloc_buffer *abuf, struct gaih_addrtuple **pat,
int *errnop, int *h_errnop, int32_t *ttlp)
{
- int first = 1;
-
enum nss_status status = NSS_STATUS_NOTFOUND;
/* Combining the NSS status of two distinct queries requires some
@@ -1157,7 +1046,10 @@ gaih_getanswer (const querybuf *answer1, int anslen1, const querybuf *answer2,
between TRYAGAIN (recoverable) and TRYAGAIN' (not-recoverable).
A recoverable TRYAGAIN is almost always due to buffer size issues
and returns ERANGE in errno and the caller is expected to retry
- with a larger buffer.
+ with a larger buffer. (The caller, _nss_dns_gethostbyname4_r,
+ ignores the return status if it detects that the result buffer
+ has been exhausted and generates a TRYAGAIN failure with an
+ ERANGE code.)
Lastly, you may be tempted to make significant changes to the
conditions in this code to bring about symmetry between responses.
@@ -1237,36 +1129,30 @@ gaih_getanswer (const querybuf *answer1, int anslen1, const querybuf *answer2,
is a recoverable error we now return TRYAGIN even if the first
response was SUCCESS. */
- if (anslen1 > 0)
- status = gaih_getanswer_slice(answer1, anslen1, qname,
- &pat, &buffer, &buflen,
- errnop, h_errnop, ttlp,
- &first);
-
- if ((status == NSS_STATUS_SUCCESS || status == NSS_STATUS_NOTFOUND
- || (status == NSS_STATUS_TRYAGAIN
- /* We want to look at the second answer in case of an
- NSS_STATUS_TRYAGAIN only if the error is non-recoverable, i.e.
- *h_errnop is NO_RECOVERY. If not, and if the failure was due to
- an insufficient buffer (ERANGE), then we need to drop the results
- and pass on the NSS_STATUS_TRYAGAIN to the caller so that it can
- repeat the query with a larger buffer. */
- && (*errnop != ERANGE || *h_errnop == NO_RECOVERY)))
- && answer2 != NULL && anslen2 > 0)
+ if (packet1len > 0)
{
- enum nss_status status2 = gaih_getanswer_slice(answer2, anslen2, qname,
- &pat, &buffer, &buflen,
- errnop, h_errnop, ttlp,
- &first);
+ status = gaih_getanswer_slice (packet1, packet1len,
+ abuf, &pat, errnop, h_errnop, ttlp, true);
+ if (alloc_buffer_has_failed (abuf))
+ /* Do not try parsing the second packet if a larger result
+ buffer is needed. The caller implements the resizing
+ protocol because *abuf has been exhausted. */
+ return NSS_STATUS_TRYAGAIN; /* Ignored by the caller. */
+ }
+
+ if ((status == NSS_STATUS_SUCCESS || status == NSS_STATUS_NOTFOUND)
+ && packet2 != NULL && packet2len > 0)
+ {
+ enum nss_status status2
+ = gaih_getanswer_slice (packet2, packet2len,
+ abuf, &pat, errnop, h_errnop, ttlp,
+ /* Success means that data with a
+ canonical name has already been
+ stored. Do not store the name again. */
+ status != NSS_STATUS_SUCCESS);
/* Use the second response status in some cases. */
if (status != NSS_STATUS_SUCCESS && status2 != NSS_STATUS_NOTFOUND)
status = status2;
- /* Do not return a truncated second response (unless it was
- unavoidable e.g. unrecoverable TRYAGAIN). */
- if (status == NSS_STATUS_SUCCESS
- && (status2 == NSS_STATUS_TRYAGAIN
- && *errnop == ERANGE && *h_errnop != NO_RECOVERY))
- status = NSS_STATUS_TRYAGAIN;
}
return status;
@@ -1274,18 +1160,13 @@ gaih_getanswer (const querybuf *answer1, int anslen1, const querybuf *answer2,
/* Variant of gaih_getanswer without a second (AAAA) response. */
static enum nss_status
-gaih_getanswer_noaaaa (const querybuf *answer1, int anslen1, const char *qname,
- struct gaih_addrtuple **pat,
- char *buffer, size_t buflen,
+gaih_getanswer_noaaaa (unsigned char *packet, size_t packetlen,
+ struct alloc_buffer *abuf, struct gaih_addrtuple **pat,
int *errnop, int *h_errnop, int32_t *ttlp)
{
- int first = 1;
-
enum nss_status status = NSS_STATUS_NOTFOUND;
- if (anslen1 > 0)
- status = gaih_getanswer_slice (answer1, anslen1, qname,
- &pat, &buffer, &buflen,
- errnop, h_errnop, ttlp,
- &first);
+ if (packetlen > 0)
+ status = gaih_getanswer_slice (packet, packetlen,
+ abuf, &pat, errnop, h_errnop, ttlp, true);
return status;
}