On Mon, 09 Aug 2010 16:23:22 +0100 David Howells <[email protected]> wrote:
> From: Wang Lei <[email protected]> > > If the DNS server returns an error, allow that to be cached in the DNS > resolver > key in lieu of a value. Userspace passes the desired error number as an > option > in the payload: > > "#dnserror=<number>" > > Userspace must map h_errno from the name resolution routines to an appropriate > Linux error before passing it up. Something like the following mapping is > recommended: > > [HOST_NOT_FOUND] = ENODATA, > [TRY_AGAIN] = EAGAIN, > [NO_RECOVERY] = ECONNREFUSED, > [NO_DATA] = ENODATA, > > in lieu of Linux errors specifically for representing name service errors. > The > filesystem must map these errors appropropriately before passing them to > userspace. AFS is made to map ENODATA and EAGAIN to EDESTADDRREQ for the > return to userspace; ECONNREFUSED is allowed to stand as is. > > The error can be seen in /proc/keys as a negative number after the description > of the key. Compare, for example, the following key entries: > > 2f97238c I--Q-- 1 53s 3f010000 0 0 dns_resol > afsdb:grand.centrall.org: -61 > 338bfbbe I--Q-- 1 59m 3f010000 0 0 dns_resol > afsdb:grand.central.org: 37 > > > If the error option is supplied in the payload, the main part of the payload > is > discarded. The key should have an expiry time set by userspace. > > Signed-off-by: Wang Lei <[email protected]> > Signed-off-by: David Howells <[email protected]> > --- > > fs/afs/cell.c | 4 ++ > net/dns_resolver/dns_key.c | 92 > ++++++++++++++++++++++++++++++++++++++++-- > net/dns_resolver/dns_query.c | 5 ++ > 3 files changed, 96 insertions(+), 5 deletions(-) > > diff --git a/fs/afs/cell.c b/fs/afs/cell.c > index ffea35c..d076588 100644 > --- a/fs/afs/cell.c > +++ b/fs/afs/cell.c > @@ -73,6 +73,10 @@ static struct afs_cell *afs_cell_alloc(const char *name, > char *vllist) > if (!vllist || strlen(vllist) < 7) { > ret = dns_query("afsdb", name, namelen, "ipv4", &dvllist, NULL); > if (ret < 0) { > + if (ret == -ENODATA || ret == -EAGAIN || ret == -ENOKEY) > + /* translate these errors into something > + * userspace might understand */ > + ret = -EDESTADDRREQ; > _leave(" = %d", ret); > return ERR_PTR(ret); > } > diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c > index 400a04d..739435a 100644 > --- a/net/dns_resolver/dns_key.c > +++ b/net/dns_resolver/dns_key.c > @@ -29,6 +29,7 @@ > #include <linux/kernel.h> > #include <linux/keyctl.h> > #include <linux/err.h> > +#include <linux/seq_file.h> > #include <keys/dns_resolver-type.h> > #include <keys/user-type.h> > #include "internal.h" > @@ -43,6 +44,8 @@ MODULE_PARM_DESC(debug, "DNS Resolver debugging mask"); > > const struct cred *dns_resolver_cache; > > +#define DNS_ERRORNO_OPTION "dnserror" > + > /* > * Instantiate a user defined key for dns_resolver. > * > @@ -59,9 +62,10 @@ static int > dns_resolver_instantiate(struct key *key, const void *_data, size_t datalen) > { > struct user_key_payload *upayload; > + unsigned long derrno; > int ret; > size_t result_len = 0; > - const char *data = _data, *opt; > + const char *data = _data, *end, *opt; > > kenter("%%%d,%s,'%s',%zu", > key->serial, key->description, data, datalen); > @@ -71,13 +75,77 @@ dns_resolver_instantiate(struct key *key, const void > *_data, size_t datalen) > datalen--; > > /* deal with any options embedded in the data */ > + end = data + datalen; > opt = memchr(data, '#', datalen); > if (!opt) { > - kdebug("no options currently supported"); > - return -EINVAL; > + /* no options: the entire data is the result */ > + kdebug("no options"); > + result_len = datalen; > + } else { > + const char *next_opt; > + > + result_len = opt - data; > + opt++; > + kdebug("options: '%s'", opt); > + do { > + const char *eq; > + int opt_len, opt_nlen, opt_vlen, tmp; > + > + next_opt = memchr(opt, '#', end - opt) ?: end; > + opt_len = next_opt - opt; > + if (!opt_len) { > + printk(KERN_WARNING > + "Empty option to dns_resolver key %d\n", > + key->serial); > + return -EINVAL; > + } > + > + eq = memchr(opt, '=', opt_len) ?: end; > + opt_nlen = eq - opt; > + eq++; > + opt_vlen = next_opt - eq; /* will be -1 if no value */ > + > + tmp = opt_vlen >= 0 ? opt_vlen : 0; > + kdebug("option '%*.*s' val '%*.*s'", > + opt_nlen, opt_nlen, opt, tmp, tmp, eq); > + > + /* see if it's an error number representing a DNS error > + * that's to be recorded as the result in this key */ > + if (opt_nlen == sizeof(DNS_ERRORNO_OPTION) - 1 && > + memcmp(opt, DNS_ERRORNO_OPTION, opt_nlen) == 0) { > + kdebug("dns error number option"); > + if (opt_vlen <= 0) > + goto bad_option_value; > + > + ret = strict_strtoul(eq, 10, &derrno); > + if (ret < 0) > + goto bad_option_value; > + > + if (derrno < 1 || derrno > 511) > + goto bad_option_value; > + > + kdebug("dns error no. = %lu", derrno); > + key->type_data.x[0] = -derrno; > + continue; > + } > + > + bad_option_value: > + printk(KERN_WARNING > + "Option '%*.*s' to dns_resolver key %d:" > + " bad/missing value\n", > + opt_nlen, opt_nlen, opt, key->serial); > + return -EINVAL; > + } while (opt = next_opt + 1, opt < end); > + } > + > + /* don't cache the result if we're caching an error saying there's no > + * result */ > + if (key->type_data.x[0]) { > + kleave(" = 0 [h_error %ld]", key->type_data.x[0]); > + return 0; > } > > - result_len = datalen; > + kdebug("store result"); > ret = key_payload_reserve(key, result_len); > if (ret < 0) > return -EINVAL; > @@ -135,13 +203,27 @@ no_match: > return ret; > } > > +/* > + * Describe a DNS key > + */ > +static void dns_resolver_describe(const struct key *key, struct seq_file *m) > +{ > + int err = key->type_data.x[0]; > + > + seq_puts(m, key->description); > + if (err) > + seq_printf(m, ": %d", err); > + else > + seq_printf(m, ": %u", key->datalen); > +} > + > struct key_type key_type_dns_resolver = { > .name = "dns_resolver", > .instantiate = dns_resolver_instantiate, > .match = dns_resolver_match, > .revoke = user_revoke, > .destroy = user_destroy, > - .describe = user_describe, > + .describe = dns_resolver_describe, > .read = user_read, > }; > > diff --git a/net/dns_resolver/dns_query.c b/net/dns_resolver/dns_query.c > index 03d5255..c32be29 100644 > --- a/net/dns_resolver/dns_query.c > +++ b/net/dns_resolver/dns_query.c > @@ -136,6 +136,11 @@ int dns_query(const char *type, const char *name, size_t > namelen, > if (ret < 0) > goto put; > > + /* If the DNS server gave an error, return that to the caller */ > + ret = rkey->type_data.x[0]; > + if (ret) > + goto put; > + > upayload = rcu_dereference_protected(rkey->payload.data, > lockdep_is_held(&rkey->sem)); > len = upayload->datalen; > Looks good to me. I guess with this, callers need to be prepared to deal with any error from userspace from 1-511, but that seems reasonable. -- Jeff Layton <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
