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[Bug libc/10484] getaddrinfo segfaults if /etc/hosts has a long line
- From: "agl at imperialviolet dot org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: Fri, 7 Jan 2011 17:41:03 +0000
- Subject: [Bug libc/10484] getaddrinfo segfaults if /etc/hosts has a long line
- Auto-submitted: auto-generated
- References: <bug-10484-131@http.sourceware.org/bugzilla/>
http://sourceware.org/bugzilla/show_bug.cgi?id=10484
Adam Langley <agl at imperialviolet dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |agl at imperialviolet dot
| |org
--- Comment #4 from Adam Langley <agl at imperialviolet dot org> 2011-01-07 17:40:48 UTC ---
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_SUCCESSÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ \
ÂÂÂÂÂÂÂÂ && _res_hconf.flags & HCONF_FLAG_MULTI)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ \
ÂÂÂÂÂÂÂÂ{ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ \
ÂÂÂÂÂÂÂÂ /* We have to get all host entries from the file. */ÂÂÂÂÂÂÂÂÂ \
ÂÂÂÂÂÂÂÂ const size_t tmp_buflen = MIN (buflen, 4096);ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ \
ÂÂÂÂÂÂÂÂ char tmp_buffer[tmp_buflen]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ \
ÂÂÂÂÂÂÂÂ __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.
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