| Summary: | libresolv res_init() does not correctly inititalize internals | ||
|---|---|---|---|
| Product: | glibc | Reporter: | Joshua Rogers <sourceware-bugs> |
| Component: | libc | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED INVALID | ||
| Severity: | normal | CC: | drepper.fsp, sourceware-bugs |
| Priority: | P2 | Flags: | fweimer:
security-
|
| Version: | unspecified | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | ||
Sorry,
if ((ret == 0) && (last_mtime != statbuf.st_mtim.tv_sec)) {
should be
if ((ret == 0) && (last_mtime != statbuf.st_mtime)) {
(for reference)
Only these are kept on res_init(), and thus are only kept with the first call to __res_maybe_init:
int retrans; /* retransmition time interval */
int retry; /* number of times to retransmit */
u_long options; /* option flags - see below. */
These are wiped, due to this bug:
int nscount; /* number of name servers */
struct sockaddr_in
nsaddr_list[MAXNS]; /* address of name server */
# define nsaddr nsaddr_list[0] /* for backward compatibility */
u_short id; /* current message id */
/* 2 byte hole here. */
char *dnsrch[MAXDNSRCH+1]; /* components of domain to search */
char defdname[256]; /* default domain (deprecated) */
u_long pfcode; /* RES_PRF_ flags - see below. */
unsigned ndots:4; /* threshold for initial abs. query */
unsigned nsort:4; /* number of elements in sort_list[] */
unsigned ipv6_unavail:1; /* connecting to IPv6 server failed */
This bug is not in the latest respoistory, and is most likely Ubuntu-specific. https://sourceware.org/git/?p=glibc.git;a=blob;f=resolv/res_libc.c;h=ee3fa2114b7051b86f6f9676f1151d1435dedb9d;hb=HEAD#l94 Reported here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1432378 |
Contrary to what one would think, res_init() does not correctly inititialize the internals for further use by the libresolv family, and others. When you call res_init(), it correctly "keeps" these: if (!_res.retrans) _res.retrans = RES_TIMEOUT; if (!_res.retry) _res.retry = 4; if (!(_res.options & RES_INIT)) _res.options = RES_DEFAULT; else if (_res.nscount > 0) __res_iclose (&_res, true); /* Close any VC sockets. */ then calls __res_vinit(): return (__res_vinit(&_res, 1)); However, programs that use the libresolv family and others, use the hidden function, "__res_maybe_init". __res_maybe_init determines if res_init(__res_vinit()) needs to be called or not. It does this: static time_t last_mtime; struct stat statbuf; int ret; if (resp->options & RES_INIT) { ret = stat (_PATH_RESCONF, &statbuf); __libc_lock_lock (lock); if ((ret == 0) && (last_mtime != statbuf.st_mtim.tv_sec)) { last_mtime = statbuf.st_mtime; atomicinc (__res_initstamp); } __libc_lock_unlock (lock); if (__res_initstamp != resp->_u._ext.initstamp) { if (resp->nscount > 0) __res_iclose (resp, true); return __res_vinit (resp, 1); } return 0; Since the internals have been initialized by res_init(), we don't need to reinitalize, normally. The program checks if we do need to reinitalize, such as due to the change in modifcation date of /etc/resolv.conf. However, "last_mtime" is never set when using res_init(), so upon the first run of __res_maybe_init(), it will always run __res_vinit(). This will wipe all changes except for the ones that are kept, mentioned above. "last_mtime" should be taken into consideration and handled, when calling res_init().