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The potential bug incurred by "one_addr".

December 16, 2010 03:36AM
In ngx_inet.c, there is a code piece of function "ngx_inet_resolve_host". If I set u->one_addr to 1, but unfortunately this hostname map to multiple IP addresses, such as
[code] myhost myhost
in /etc/hosts.

h->h_addr_list will be 2 entries before NULL. Each of them will be converted to human readable format and assigned to u->addrs[ i ]. However, when one_addr is set, [b]u->addrs will be allocated ONLY ONE ngx_addr_t mem.[/b] In this way, a mem crash is inevitable.

I set one_addr to 1 because I'm writing a custom module and want to connect another server. Sadly the server is also running on the local host with multiple IP in /etc/hosts. I want to connect the first IP match that host name ( because that server require a non-lookback IP. I thought "one_addr" means "fetch the first found IP". But seems I was wrong.

Besides this, I insist alloc mem with "i", but loop will h->h_addr_list is very dangerous. Report an error is more suitable rather than leave a time bomb.

Affected version: all versions!!!

----------------------------------------------related coe---------------------------------------------
if (u->one_addr == 0) {
for (i = 0; h->h_addr_list[i] != NULL; i++) { /* void */ }

} else {
i = 1;

/* MP: ngx_shared_palloc() */

u->addrs = ngx_pcalloc(pool, i * sizeof(ngx_addr_t));
if (u->addrs == NULL) {
return NGX_ERROR;

u->naddrs = i;

for (i = 0; h->h_addr_list[ i ] != NULL; i++) {

sin = ngx_pcalloc(pool, sizeof(struct sockaddr_in));
if (sin == NULL) {
return NGX_ERROR;

sin->sin_family = AF_INET;
sin->sin_port = port;
sin->sin_addr.s_addr = *(in_addr_t *) (h->h_addr_list[ i ]);

u->addrs[ i ].sockaddr = (struct sockaddr *) sin;
u->addrs[ i ].socklen = sizeof(struct sockaddr_in);

len = NGX_INET_ADDRSTRLEN + sizeof(":65535") - 1;

p = ngx_pnalloc(pool, len);
if (p == NULL) {
return NGX_ERROR;

len = ngx_sock_ntop((struct sockaddr *) sin, p, len, 1);

u->addrs[ i ].name.len = len;
u->addrs[ i ].name.data = p;
Subject Author Posted

The potential bug incurred by "one_addr".

speedfirst December 16, 2010 03:36AM

Re: The potential bug incurred by "one_addr".

Maxim Dounin December 16, 2010 08:30AM

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