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![Greg Banks](/assets/img/avatar_default.png)
Fix a regression in the reply cache introduced when the code was converted to use proper Linux lists. When a new entry needs to be inserted, the case where all the entries are currently being used by threads is not correctly detected. This can result in memory corruption and a crash. In the current code this is an extremely unlikely corner case; it would require the machine to have 1024 nfsd threads and all of them to be busy at the same time. However, upcoming reply cache changes make this more likely; a crash due to this problem was actually observed in field. Signed-off-by: Greg Banks <gnb@sgi.com> Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
330 lines
7.8 KiB
C
330 lines
7.8 KiB
C
/*
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* linux/fs/nfsd/nfscache.c
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*
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* Request reply cache. This is currently a global cache, but this may
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* change in the future and be a per-client cache.
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*
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* This code is heavily inspired by the 44BSD implementation, although
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* it does things a bit differently.
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*
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* Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
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*/
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#include <linux/kernel.h>
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#include <linux/time.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <linux/spinlock.h>
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#include <linux/list.h>
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#include <linux/sunrpc/svc.h>
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#include <linux/nfsd/nfsd.h>
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#include <linux/nfsd/cache.h>
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/* Size of reply cache. Common values are:
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* 4.3BSD: 128
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* 4.4BSD: 256
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* Solaris2: 1024
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* DEC Unix: 512-4096
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*/
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#define CACHESIZE 1024
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#define HASHSIZE 64
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static struct hlist_head * cache_hash;
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static struct list_head lru_head;
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static int cache_disabled = 1;
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/*
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* Calculate the hash index from an XID.
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*/
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static inline u32 request_hash(u32 xid)
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{
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u32 h = xid;
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h ^= (xid >> 24);
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return h & (HASHSIZE-1);
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}
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static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
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/*
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* locking for the reply cache:
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* A cache entry is "single use" if c_state == RC_INPROG
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* Otherwise, it when accessing _prev or _next, the lock must be held.
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*/
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static DEFINE_SPINLOCK(cache_lock);
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int nfsd_reply_cache_init(void)
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{
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struct svc_cacherep *rp;
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int i;
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INIT_LIST_HEAD(&lru_head);
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i = CACHESIZE;
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while (i) {
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rp = kmalloc(sizeof(*rp), GFP_KERNEL);
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if (!rp)
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goto out_nomem;
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list_add(&rp->c_lru, &lru_head);
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rp->c_state = RC_UNUSED;
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rp->c_type = RC_NOCACHE;
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INIT_HLIST_NODE(&rp->c_hash);
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i--;
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}
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cache_hash = kcalloc (HASHSIZE, sizeof(struct hlist_head), GFP_KERNEL);
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if (!cache_hash)
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goto out_nomem;
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cache_disabled = 0;
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return 0;
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out_nomem:
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printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
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nfsd_reply_cache_shutdown();
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return -ENOMEM;
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}
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void nfsd_reply_cache_shutdown(void)
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{
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struct svc_cacherep *rp;
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while (!list_empty(&lru_head)) {
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rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
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if (rp->c_state == RC_DONE && rp->c_type == RC_REPLBUFF)
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kfree(rp->c_replvec.iov_base);
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list_del(&rp->c_lru);
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kfree(rp);
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}
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cache_disabled = 1;
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kfree (cache_hash);
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cache_hash = NULL;
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}
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/*
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* Move cache entry to end of LRU list
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*/
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static void
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lru_put_end(struct svc_cacherep *rp)
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{
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list_move_tail(&rp->c_lru, &lru_head);
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}
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/*
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* Move a cache entry from one hash list to another
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*/
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static void
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hash_refile(struct svc_cacherep *rp)
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{
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hlist_del_init(&rp->c_hash);
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hlist_add_head(&rp->c_hash, cache_hash + request_hash(rp->c_xid));
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}
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/*
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* Try to find an entry matching the current call in the cache. When none
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* is found, we grab the oldest unlocked entry off the LRU list.
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* Note that no operation within the loop may sleep.
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*/
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int
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nfsd_cache_lookup(struct svc_rqst *rqstp, int type)
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{
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struct hlist_node *hn;
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struct hlist_head *rh;
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struct svc_cacherep *rp;
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__be32 xid = rqstp->rq_xid;
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u32 proto = rqstp->rq_prot,
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vers = rqstp->rq_vers,
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proc = rqstp->rq_proc;
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unsigned long age;
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int rtn;
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rqstp->rq_cacherep = NULL;
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if (cache_disabled || type == RC_NOCACHE) {
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nfsdstats.rcnocache++;
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return RC_DOIT;
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}
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spin_lock(&cache_lock);
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rtn = RC_DOIT;
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rh = &cache_hash[request_hash(xid)];
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hlist_for_each_entry(rp, hn, rh, c_hash) {
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if (rp->c_state != RC_UNUSED &&
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xid == rp->c_xid && proc == rp->c_proc &&
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proto == rp->c_prot && vers == rp->c_vers &&
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time_before(jiffies, rp->c_timestamp + 120*HZ) &&
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memcmp((char*)&rqstp->rq_addr, (char*)&rp->c_addr, sizeof(rp->c_addr))==0) {
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nfsdstats.rchits++;
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goto found_entry;
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}
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}
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nfsdstats.rcmisses++;
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/* This loop shouldn't take more than a few iterations normally */
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{
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int safe = 0;
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list_for_each_entry(rp, &lru_head, c_lru) {
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if (rp->c_state != RC_INPROG)
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break;
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if (safe++ > CACHESIZE) {
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printk("nfsd: loop in repcache LRU list\n");
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cache_disabled = 1;
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goto out;
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}
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}
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}
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/* All entries on the LRU are in-progress. This should not happen */
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if (&rp->c_lru == &lru_head) {
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static int complaints;
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printk(KERN_WARNING "nfsd: all repcache entries locked!\n");
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if (++complaints > 5) {
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printk(KERN_WARNING "nfsd: disabling repcache.\n");
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cache_disabled = 1;
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}
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goto out;
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}
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rqstp->rq_cacherep = rp;
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rp->c_state = RC_INPROG;
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rp->c_xid = xid;
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rp->c_proc = proc;
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memcpy(&rp->c_addr, svc_addr_in(rqstp), sizeof(rp->c_addr));
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rp->c_prot = proto;
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rp->c_vers = vers;
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rp->c_timestamp = jiffies;
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hash_refile(rp);
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/* release any buffer */
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if (rp->c_type == RC_REPLBUFF) {
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kfree(rp->c_replvec.iov_base);
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rp->c_replvec.iov_base = NULL;
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}
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rp->c_type = RC_NOCACHE;
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out:
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spin_unlock(&cache_lock);
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return rtn;
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found_entry:
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/* We found a matching entry which is either in progress or done. */
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age = jiffies - rp->c_timestamp;
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rp->c_timestamp = jiffies;
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lru_put_end(rp);
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rtn = RC_DROPIT;
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/* Request being processed or excessive rexmits */
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if (rp->c_state == RC_INPROG || age < RC_DELAY)
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goto out;
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/* From the hall of fame of impractical attacks:
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* Is this a user who tries to snoop on the cache? */
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rtn = RC_DOIT;
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if (!rqstp->rq_secure && rp->c_secure)
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goto out;
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/* Compose RPC reply header */
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switch (rp->c_type) {
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case RC_NOCACHE:
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break;
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case RC_REPLSTAT:
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svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
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rtn = RC_REPLY;
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break;
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case RC_REPLBUFF:
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if (!nfsd_cache_append(rqstp, &rp->c_replvec))
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goto out; /* should not happen */
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rtn = RC_REPLY;
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break;
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default:
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printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
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rp->c_state = RC_UNUSED;
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}
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goto out;
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}
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/*
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* Update a cache entry. This is called from nfsd_dispatch when
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* the procedure has been executed and the complete reply is in
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* rqstp->rq_res.
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*
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* We're copying around data here rather than swapping buffers because
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* the toplevel loop requires max-sized buffers, which would be a waste
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* of memory for a cache with a max reply size of 100 bytes (diropokres).
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*
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* If we should start to use different types of cache entries tailored
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* specifically for attrstat and fh's, we may save even more space.
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*
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* Also note that a cachetype of RC_NOCACHE can legally be passed when
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* nfsd failed to encode a reply that otherwise would have been cached.
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* In this case, nfsd_cache_update is called with statp == NULL.
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*/
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void
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nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
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{
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struct svc_cacherep *rp;
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struct kvec *resv = &rqstp->rq_res.head[0], *cachv;
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int len;
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if (!(rp = rqstp->rq_cacherep) || cache_disabled)
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return;
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len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
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len >>= 2;
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/* Don't cache excessive amounts of data and XDR failures */
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if (!statp || len > (256 >> 2)) {
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rp->c_state = RC_UNUSED;
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return;
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}
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switch (cachetype) {
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case RC_REPLSTAT:
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if (len != 1)
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printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
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rp->c_replstat = *statp;
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break;
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case RC_REPLBUFF:
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cachv = &rp->c_replvec;
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cachv->iov_base = kmalloc(len << 2, GFP_KERNEL);
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if (!cachv->iov_base) {
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spin_lock(&cache_lock);
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rp->c_state = RC_UNUSED;
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spin_unlock(&cache_lock);
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return;
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}
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cachv->iov_len = len << 2;
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memcpy(cachv->iov_base, statp, len << 2);
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break;
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}
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spin_lock(&cache_lock);
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lru_put_end(rp);
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rp->c_secure = rqstp->rq_secure;
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rp->c_type = cachetype;
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rp->c_state = RC_DONE;
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rp->c_timestamp = jiffies;
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spin_unlock(&cache_lock);
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return;
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}
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/*
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* Copy cached reply to current reply buffer. Should always fit.
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* FIXME as reply is in a page, we should just attach the page, and
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* keep a refcount....
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*/
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static int
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nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
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{
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struct kvec *vec = &rqstp->rq_res.head[0];
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if (vec->iov_len + data->iov_len > PAGE_SIZE) {
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printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
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data->iov_len);
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return 0;
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}
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memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
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vec->iov_len += data->iov_len;
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return 1;
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}
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