mirror of git://sourceware.org/git/glibc.git
16b293a7a6
[Fixes BZ #14308, #12994, #13651] AF_UNSPEC results in sending two queries in parallel, one for the A record and the other for the AAAA record. If one of these is a referral, then the query fails, which is wrong. It should return at least the one successful response. The fix has two parts. The first part makes the referral fall back to the SERVFAIL path, which results in using the successful response. There is a bug in that path however, due to which the second part is necessary. The bug here is that if the first response is a failure and the second succeeds, __libc_res_nsearch does not detect that and assumes a failure. The case where the first response is a success and the second fails, works correctly. This condition is produced by buggy routers, so here's a crude interposable library that can simulate such a condition. The library overrides the recvfrom syscall and modifies the header of the packet received to reproduce this scenario. It has two key variables: mod_packet and first_error. The mod_packet variable when set to 0, results in odd packets being modified to be a referral. When set to 1, even packets are modified to be a referral. The first_error causes the first response to be a failure so that a domain-appended search is performed to test the second part of the __libc_nsearch fix. The driver for this fix is a simple getaddrinfo program that does an AF_UNSPEC query. I have omitted this since it should be easy to implement. I have tested this on x86_64. The interceptor library source: /* Override recvfrom and modify the header of the first DNS response to make it a referral and reproduce bz #845218. We have to resort to this ugly hack because we cannot make bind return the buggy response of a referral for the AAAA record and an authoritative response for the A record. */ #define _GNU_SOURCE #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdio.h> #include <stdbool.h> #include <endian.h> #include <dlfcn.h> #include <stdlib.h> /* Lifted from resolv/arpa/nameser_compat.h. */ typedef struct { unsigned id :16; /*%< query identification number */ #if BYTE_ORDER == BIG_ENDIAN /* fields in third byte */ unsigned qr: 1; /*%< response flag */ unsigned opcode: 4; /*%< purpose of message */ unsigned aa: 1; /*%< authoritive answer */ unsigned tc: 1; /*%< truncated message */ unsigned rd: 1; /*%< recursion desired */ /* fields * in * fourth * byte * */ unsigned ra: 1; /*%< recursion available */ unsigned unused :1; /*%< unused bits (MBZ as of 4.9.3a3) */ unsigned ad: 1; /*%< authentic data from named */ unsigned cd: 1; /*%< checking disabled by resolver */ unsigned rcode :4; /*%< response code */ #endif #if BYTE_ORDER == LITTLE_ENDIAN || BYTE_ORDER == PDP_ENDIAN /* fields * in * third * byte * */ unsigned rd :1; /*%< recursion desired */ unsigned tc :1; /*%< truncated message */ unsigned aa :1; /*%< authoritive answer */ unsigned opcode :4; /*%< purpose of message */ unsigned qr :1; /*%< response flag */ /* fields * in * fourth * byte * */ unsigned rcode :4; /*%< response code */ unsigned cd: 1; /*%< checking disabled by resolver */ unsigned ad: 1; /*%< authentic data from named */ unsigned unused :1; /*%< unused bits (MBZ as of 4.9.3a3) */ unsigned ra :1; /*%< recursion available */ #endif /* remaining * bytes * */ unsigned qdcount :16; /*%< number of question entries */ unsigned ancount :16; /*%< number of answer entries */ unsigned nscount :16; /*%< number of authority entries */ unsigned arcount :16; /*%< number of resource entries */ } HEADER; static int done = 0; /* Packets to modify. 0 for the odd packets and 1 for even packets. */ static const int mod_packet = 0; /* Set to true if the first request should result in an error, resulting in a search query. */ static bool first_error = true; static ssize_t (*real_recvfrom) (int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen); void __attribute__ ((constructor)) init (void) { real_recvfrom = dlsym (RTLD_NEXT, "recvfrom"); if (real_recvfrom == NULL) { printf ("Failed to get reference to recvfrom: %s\n", dlerror ()); printf ("Cannot simulate test\n"); abort (); } } /* Modify the second packet that we receive to set the header in a manner as to reproduce BZ #845218. */ static void mod_buf (HEADER *h, int port) { if (done % 2 == mod_packet || (first_error && done == 1)) { printf ("(Modifying header)"); if (first_error && done == 1) h->rcode = 3; else h->rcode = 0; /* NOERROR == 0. */ h->ancount = 0; h->aa = 0; h->ra = 0; h->arcount = 0; } done++; } ssize_t recvfrom (int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen) { ssize_t ret = real_recvfrom (sockfd, buf, len, flags, src_addr, addrlen); int port = htons (((struct sockaddr_in *) src_addr)->sin_port); struct in_addr addr = ((struct sockaddr_in *) src_addr)->sin_addr; const char *host = inet_ntoa (addr); printf ("\n*** From %s:%d: ", host, port); mod_buf (buf, port); printf ("returned %zd\n", ret); return ret; } |
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README
This directory contains the sources of the GNU C Library. See the file "version.h" for what release version you have. The GNU C Library is the standard system C library for all GNU systems, and is an important part of what makes up a GNU system. It provides the system API for all programs written in C and C-compatible languages such as C++ and Objective C; the runtime facilities of other programming languages use the C library to access the underlying operating system. In GNU/Linux systems, the C library works with the Linux kernel to implement the operating system behavior seen by user applications. In GNU/Hurd systems, it works with a microkernel and Hurd servers. The GNU C Library implements much of the POSIX.1 functionality in the GNU/Hurd system, using configurations i[4567]86-*-gnu. The current GNU/Hurd support requires out-of-tree patches that will eventually be incorporated into an official GNU C Library release. When working with Linux kernels, this version of the GNU C Library requires Linux kernel version 2.6.16 or later. Also note that the shared version of the libgcc_s library must be installed for the pthread library to work correctly. The GNU C Library supports these configurations for using Linux kernels: aarch64*-*-linux-gnu alpha*-*-linux-gnu arm-*-linux-gnueabi hppa-*-linux-gnu Not currently functional without patches. i[4567]86-*-linux-gnu x86_64-*-linux-gnu Can build either x86_64 or x32 ia64-*-linux-gnu m68k-*-linux-gnu microblaze*-*-linux-gnu mips-*-linux-gnu mips64-*-linux-gnu powerpc-*-linux-gnu Hardware or software floating point, BE only. powerpc64*-*-linux-gnu Big-endian and little-endian. s390-*-linux-gnu s390x-*-linux-gnu sh[34]-*-linux-gnu sparc*-*-linux-gnu sparc64*-*-linux-gnu tilegx-*-linux-gnu tilepro-*-linux-gnu The code for other CPU configurations supported by volunteers outside of the core glibc maintenance effort is contained in the `ports' add-on, located in the `ports' subdirectory of the source tree. If you are interested in doing a port, please contact the glibc maintainers; see http://www.gnu.org/software/libc/ for more information. See the file INSTALL to find out how to configure, build, and install the GNU C Library. You might also consider reading the WWW pages for the C library at http://www.gnu.org/software/libc/. The GNU C Library is (almost) completely documented by the Texinfo manual found in the `manual/' subdirectory. The manual is still being updated and contains some known errors and omissions; we regret that we do not have the resources to work on the manual as much as we would like. For corrections to the manual, please file a bug in the `manual' component, following the bug-reporting instructions below. Please be sure to check the manual in the current development sources to see if your problem has already been corrected. Please see http://www.gnu.org/software/libc/bugs.html for bug reporting information. We are now using the Bugzilla system to track all bug reports. This web page gives detailed information on how to report bugs properly. The GNU C Library is free software. See the file COPYING.LIB for copying conditions, and LICENSES for notices about a few contributions that require these additional notices to be distributed. License copyright years may be listed using range notation, e.g., 2000-2013, indicating that every year in the range, inclusive, is a copyrightable year that would otherwise be listed individually.