If /etc/hosts contains a long line (thousands of bytes), getaddrinfo causes a segmentation fault. A small program to test: -- 8< --- #include <stddef.h> #include <sys/types.h> #include <sys/socket.h> #include <netdb.h> int main(void) { struct addrinfo *result; getaddrinfo("localhost", NULL, NULL, &result); return 0; } --- 8< --- On a system with short lines in /etc/hosts, the above program exits normally. If /etc/hosts has a very long line (5500 bytes is sufficiently long), it segmentation faults. I think this is due to using alloca and extend_alloca to hold the line when parsing the file, which leads to a stack overflow, which then results in the kernel sending a SIGSEGV to the program. The parsing code is not set up to handle that. Unfortunately, I am too stupid to provide a patch to fix this. My test /etc/hosts file has IPv6 addresses commented out, so the segmentation fault happens in sysdeps/posix/getaddrinfo.c, function gaih_inet, around line 531, on this line: rc = __gethostbyname2_r (name, family, &th, tmpbuf, tmpbuflen, &h, &herrno); My stack limit is 8 megabytes. This was originally filed as a bug in Ubuntu, and applies to both versions 2.9 and 2.10 in that distribution. I have compared the source file against the current version in git, and it has no relevant changes. (I was unable to set up a chroot to actually test the current git version, sorry.) Original bug: https://bugs.launchpad.net/ubuntu/+source/eglibc/+bug/386791
This also happens on plain x86 processors. The original bug was found on a PIV. Perhaps it shouldn't be marked as x86_64.
You have to be much more precise. I cannot reproduce any problem and your description doesn't say where the stack overflow is supposed to happen.
Try a longer line. I've gotten 100k+ lines just by using a hosts file for adblock and then running network-admin.
The following program will blow its stack and crash if I have an /etc/hosts line longer than 4Kish. --- #include <string.h> #include <sys/types.h> #include <sys/socket.h> #include <netdb.h> int main() { struct addrinfo hints, *res; memset(&hints, 0, sizeof(hints)); hints.ai_family = PF_INET; getaddrinfo("www.google.com", "http", &hints, &res); return 0; } --- Setting the ai_family in the hints is required in order to reproduce the crash. (File and line references in the following are relative to git 16c2895feabae0962e0eba2b9164c6a83014bfe4) In sysdeps/posix/getaddrinfo.c:531 we have a loop in gaih_inet which allocas a buffer and doubles the size of that buffer each time __gethostbyname2_r returns with ERANGE. The __gethostbyname2_r ends up in nss/nss_files/files-hosts.c:128: if (status == NSS_STATUS_SUCCESS»·»·······»·······»·······»······· \ »······· && _res_hconf.flags & HCONF_FLAG_MULTI)»······»·······»······· \ »·······{»······»·······»·······»·······»·······»·······»·······»······· \ »······· /* We have to get all host entries from the file. */»»······· \ »······· const size_t tmp_buflen = MIN (buflen, 4096);»»·······»······· \ »······· char tmp_buffer[tmp_buflen]»··»·······»·······»·······»······· \ »······· __attribute__ ((__aligned__ (__alignof__ (struct hostent_data))));\ Here, if HCONF_FLAG_MULTI is set then a secondary buffer is created on the stack for the use of internal_getent. This buffer is limited to 4K in size. internal_getent will try to read lines from /etc/hosts and it will return ERANGE if the line (plus an internal structure) doesn't fit into |tmp_buffer|. When this happens the loop in getaddrinfo.c will try doubling the size of its buffer. However, |tmp_buffer| was limited to 4K so __gethostbyname2_r repeatedly returns ERANGE and gaih_inet uselessly expands the buffer on the stack until the program crashes. I believe that the best solution is to replace: const size_t tmp_buflen = MIN (buflen, 4096); with: const size_t tmp_buflen = buflen; I can confirm that this fixes the crash for me.
I've checked in a patch.
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No trust boundary is crossed because write access to /etc/hosts is very restricted. I don't think it is even updated when connecting to different networks using tools such as NetworkManager.