* [musl] Out-of-bounds reads in DNS response parsing
@ 2023-02-23 20:34 Alexey Izbyshev
0 siblings, 0 replies; only message in thread
From: Alexey Izbyshev @ 2023-02-23 20:34 UTC (permalink / raw)
To: musl
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Hi,
I've found several issues with DNS response parsing that can result in
getaddrinfo/getnameinfo reading unininitialized or (nearby)
out-of-bounds data on stack and returning garbage. The issues are
described in the attached patches.
Alexey
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From bbbbd53761b484422c7031fe97ad7ea92a0bdb04 Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Sat, 28 Jan 2023 00:17:37 +0300
Subject: [PATCH 1/2] fix out-of-bounds reads in __dns_parse
Mail-Followup-To: musl@lists.openwall.com
There are several issues with range checks in this function:
* The question section parsing loop can read up to two out-of-bounds
bytes before doing the range check and bailing out.
* The answer section parsing loop, in addition to the same issue as
above, uses the wrong length in the range check that doesn't prevent
OOB reads when computing len later.
* The len range check before calling the callback is off by 10. Also,
p+len can overflow in a (probably theoretical) case when p is within
2^16 from UINTPTR_MAX.
Because __dns_parse is used only with stack-allocated buffers, such
small overreads can't result in a segfault. The first two also don't
affect the function result, but the last one may result in getaddrinfo
incorrectly succeeding and returning up to 10 bytes past the
response buffer as a part of the IP address, and in (canon) name
returned by getaddrinfo/getnameinfo being affected by memory past the
response buffer (because dn_expand might interpret it as a pointer).
---
src/network/dns_parse.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/src/network/dns_parse.c b/src/network/dns_parse.c
index e6ee19d9..320df60d 100644
--- a/src/network/dns_parse.c
+++ b/src/network/dns_parse.c
@@ -15,17 +15,17 @@ int __dns_parse(const unsigned char *r, int rlen, int (*callback)(void *, int, c
if (qdcount+ancount > 64) return -1;
while (qdcount--) {
while (p-r < rlen && *p-1U < 127) p++;
- if (*p>193 || (*p==193 && p[1]>254) || p>r+rlen-6)
+ if (p>r+rlen-6 || *p>193 || (*p==193 && p[1]>254))
return -1;
p += 5 + !!*p;
}
while (ancount--) {
while (p-r < rlen && *p-1U < 127) p++;
- if (*p>193 || (*p==193 && p[1]>254) || p>r+rlen-6)
+ if (p>r+rlen-12 || *p>193 || (*p==193 && p[1]>254))
return -1;
p += 1 + !!*p;
len = p[8]*256 + p[9];
- if (p+len > r+rlen) return -1;
+ if (len+10 > r+rlen-p) return -1;
if (callback(ctx, p[1], p+10, len, r) < 0) return -1;
p += 10 + len;
}
--
2.39.1
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From 1eb7fd50d7c045c1203f700cb08169308435ae72 Mon Sep 17 00:00:00 2001
From: Alexey Izbyshev <izbyshev@ispras.ru>
Date: Sun, 29 Jan 2023 19:46:51 +0300
Subject: [PATCH 2/2] prevent CNAME/PTR parsing from reading data past the
response end
Mail-Followup-To: musl@lists.openwall.com
DNS parsing callbacks pass the response buffer end instead of the actual
response end to dn_expand, so a malformed DNS response can use message
compression to make dn_expand jump past the response end and attempt to
parse uninitialized parts of that buffer, which might succeed and return
garbage.
---
src/network/dns_parse.c | 4 ++--
src/network/getnameinfo.c | 4 ++--
src/network/lookup.h | 2 +-
src/network/lookup_name.c | 4 ++--
4 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/src/network/dns_parse.c b/src/network/dns_parse.c
index 320df60d..7f83e791 100644
--- a/src/network/dns_parse.c
+++ b/src/network/dns_parse.c
@@ -1,7 +1,7 @@
#include <string.h>
#include "lookup.h"
-int __dns_parse(const unsigned char *r, int rlen, int (*callback)(void *, int, const void *, int, const void *), void *ctx)
+int __dns_parse(const unsigned char *r, int rlen, int (*callback)(void *, int, const void *, int, const void *, int), void *ctx)
{
int qdcount, ancount;
const unsigned char *p;
@@ -26,7 +26,7 @@ int __dns_parse(const unsigned char *r, int rlen, int (*callback)(void *, int, c
p += 1 + !!*p;
len = p[8]*256 + p[9];
if (len+10 > r+rlen-p) return -1;
- if (callback(ctx, p[1], p+10, len, r) < 0) return -1;
+ if (callback(ctx, p[1], p+10, len, r, rlen) < 0) return -1;
p += 10 + len;
}
return 0;
diff --git a/src/network/getnameinfo.c b/src/network/getnameinfo.c
index 949e1811..080d3c06 100644
--- a/src/network/getnameinfo.c
+++ b/src/network/getnameinfo.c
@@ -108,10 +108,10 @@ static void reverse_services(char *buf, int port, int dgram)
__fclose_ca(f);
}
-static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
+static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet, int plen)
{
if (rr != RR_PTR) return 0;
- if (__dn_expand(packet, (const unsigned char *)packet + 512,
+ if (__dn_expand(packet, (const unsigned char *)packet + plen,
data, c, 256) <= 0)
*(char *)c = 0;
return 0;
diff --git a/src/network/lookup.h b/src/network/lookup.h
index ef662725..54b2f8b5 100644
--- a/src/network/lookup.h
+++ b/src/network/lookup.h
@@ -50,6 +50,6 @@ hidden int __lookup_ipliteral(struct address buf[static 1], const char *name, in
hidden int __get_resolv_conf(struct resolvconf *, char *, size_t);
hidden int __res_msend_rc(int, const unsigned char *const *, const int *, unsigned char *const *, int *, int, const struct resolvconf *);
-hidden int __dns_parse(const unsigned char *, int, int (*)(void *, int, const void *, int, const void *), void *);
+hidden int __dns_parse(const unsigned char *, int, int (*)(void *, int, const void *, int, const void *, int), void *);
#endif
diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
index 5f6867cb..f268bcda 100644
--- a/src/network/lookup_name.c
+++ b/src/network/lookup_name.c
@@ -111,13 +111,13 @@ struct dpc_ctx {
#define ABUF_SIZE 768
-static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet)
+static int dns_parse_callback(void *c, int rr, const void *data, int len, const void *packet, int plen)
{
char tmp[256];
int family;
struct dpc_ctx *ctx = c;
if (rr == RR_CNAME) {
- if (__dn_expand(packet, (const unsigned char *)packet + ABUF_SIZE,
+ if (__dn_expand(packet, (const unsigned char *)packet + plen,
data, tmp, sizeof tmp) > 0 && is_valid_hostname(tmp))
strcpy(ctx->canon, tmp);
return 0;
--
2.39.1
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2023-02-23 20:34 [musl] Out-of-bounds reads in DNS response parsing Alexey Izbyshev
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