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[Bug network/19791] Assertion failure in res_query.c with un-connectable name server addresses
- From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Sat, 28 May 2016 21:00:43 +0000
- Subject: [Bug network/19791] Assertion failure in res_query.c with un-connectable name server addresses
- Auto-submitted: auto-generated
- References: <bug-19791-131 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=19791
--- Comment #24 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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The branch, release/2.19/master has been updated
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via c08e8bd0ef1d16d0139dbc80a976e2cbf2517f02 (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=10d268070a8aa9a878668e7f060e92ed668de146
commit 10d268070a8aa9a878668e7f060e92ed668de146
Author: Florian Weimer <fweimer@redhat.com>
Date: Fri Mar 25 11:49:51 2016 +0100
resolv: Always set *resplen2 out parameter in send_dg [BZ #19791]
Since commit 44d20bca52ace85850012b0ead37b360e3ecd96e (Implement
second fallback mode for DNS requests), there is a code path which
returns early, before *resplen2 is initialized. This happens if the
name server address is immediately recognized as invalid (because of
lack of protocol support, or if it is a broadcast address such
255.255.255.255, or another invalid address).
If this happens and *resplen2 was non-zero (which is the case if a
previous query resulted in a failure), __libc_res_nquery would reuse
an existing second answer buffer. This answer has been previously
identified as unusable (for example, it could be an NXDOMAIN
response). Due to the presence of a second answer, no name server
switching will occur. The result is a name resolution failure,
although a successful resolution would have been possible if name
servers have been switched and queries had proceeded along the search
path.
The above paragraph still simplifies the situation. Before glibc
2.23, if the second answer needed malloc, the stub resolver would
still attempt to reuse the second answer, but this is not possible
because __libc_res_nsearch has freed it, after the unsuccessful call
to __libc_res_nquerydomain, and set the buffer pointer to NULL. This
eventually leads to an assertion failure in __libc_res_nquery:
/* Make sure both hp and hp2 are defined */
assert((hp != NULL) && (hp2 != NULL));
If assertions are disabled, the consequence is a NULL pointer
dereference on the next line.
Starting with glibc 2.23, as a result of commit
e9db92d3acfe1822d56d11abcea5bfc4c41cf6ca (CVE-2015-7547: getaddrinfo()
stack-based buffer overflow (Bug 18665)), the second answer is always
allocated with malloc. This means that the assertion failure happens
with small responses as well because there is no buffer to reuse, as
soon as there is a name resolution failure which triggers a search for
an answer along the search path.
This commit addresses the issue by ensuring that *resplen2 is
initialized before the send_dg function returns.
This commit also addresses a bug where an invalid second reply is
incorrectly returned as a valid to the caller.
(cherry picked from commit b66d837bb5398795c6b0f651bd5a5d66091d8577)
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c08e8bd0ef1d16d0139dbc80a976e2cbf2517f02
commit c08e8bd0ef1d16d0139dbc80a976e2cbf2517f02
Author: Carlos O'Donell <carlos@systemhalted.org>
Date: Tue Feb 16 21:26:37 2016 -0500
CVE-2015-7547: getaddrinfo() stack-based buffer overflow (Bug 18665).
* A stack-based buffer overflow was found in libresolv when invoked from
libnss_dns, allowing specially crafted DNS responses to seize control
of execution flow in the DNS client. The buffer overflow occurs in
the functions send_dg (send datagram) and send_vc (send TCP) for the
NSS module libnss_dns.so.2 when calling getaddrinfo with AF_UNSPEC
family. The use of AF_UNSPEC triggers the low-level resolver code to
send out two parallel queries for A and AAAA. A mismanagement of the
buffers used for those queries could result in the response of a query
writing beyond the alloca allocated buffer created by
_nss_dns_gethostbyname4_r. Buffer management is simplified to remove
the overflow. Thanks to the Google Security Team and Red Hat for
reporting the security impact of this issue, and Robert Holiday of
Ciena for reporting the related bug 18665. (CVE-2015-7547)
See also:
https://sourceware.org/ml/libc-alpha/2016-02/msg00416.html
https://sourceware.org/ml/libc-alpha/2016-02/msg00418.html
(cherry picked from commit e9db92d3acfe1822d56d11abcea5bfc4c41cf6ca)
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 24 ++++
NEWS | 17 +++-
resolv/nss_dns/dns-host.c | 111 +++++++++++++++-
resolv/res_query.c | 3 +
resolv/res_send.c | 320 +++++++++++++++++++++++++++++++++------------
5 files changed, 389 insertions(+), 86 deletions(-)
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