linux/fs/nfsd/nfscache.c
Jeff Layton 781c2a5a5f nfsd: when reusing an existing repcache entry, unhash it first
The DRC code will attempt to reuse an existing, expired cache entry in
preference to allocating a new one. It'll then search the cache, and if
it gets a hit it'll then free the cache entry that it was going to
reuse.

The cache code doesn't unhash the entry that it's going to reuse
however, so it's possible for it end up designating an entry for reuse
and then subsequently freeing the same entry after it finds it.  This
leads it to a later use-after-free situation and usually some list
corruption warnings or an oops.

Fix this by simply unhashing the entry that we intend to reuse. That
will mean that it's not findable via a search and should prevent this
situation from occurring.

Cc: stable@vger.kernel.org # v3.10+
Reported-by: Christoph Hellwig <hch@infradead.org>
Reported-by: g. artim <gartim@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
2013-12-10 20:34:44 -05:00

642 lines
16 KiB
C

/*
* Request reply cache. This is currently a global cache, but this may
* change in the future and be a per-client cache.
*
* This code is heavily inspired by the 44BSD implementation, although
* it does things a bit differently.
*
* Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
*/
#include <linux/slab.h>
#include <linux/sunrpc/addr.h>
#include <linux/highmem.h>
#include <linux/log2.h>
#include <linux/hash.h>
#include <net/checksum.h>
#include "nfsd.h"
#include "cache.h"
#define NFSDDBG_FACILITY NFSDDBG_REPCACHE
/*
* We use this value to determine the number of hash buckets from the max
* cache size, the idea being that when the cache is at its maximum number
* of entries, then this should be the average number of entries per bucket.
*/
#define TARGET_BUCKET_SIZE 64
static struct hlist_head * cache_hash;
static struct list_head lru_head;
static struct kmem_cache *drc_slab;
/* max number of entries allowed in the cache */
static unsigned int max_drc_entries;
/* number of significant bits in the hash value */
static unsigned int maskbits;
/*
* Stats and other tracking of on the duplicate reply cache. All of these and
* the "rc" fields in nfsdstats are protected by the cache_lock
*/
/* total number of entries */
static unsigned int num_drc_entries;
/* cache misses due only to checksum comparison failures */
static unsigned int payload_misses;
/* amount of memory (in bytes) currently consumed by the DRC */
static unsigned int drc_mem_usage;
/* longest hash chain seen */
static unsigned int longest_chain;
/* size of cache when we saw the longest hash chain */
static unsigned int longest_chain_cachesize;
static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
static void cache_cleaner_func(struct work_struct *unused);
static unsigned long nfsd_reply_cache_count(struct shrinker *shrink,
struct shrink_control *sc);
static unsigned long nfsd_reply_cache_scan(struct shrinker *shrink,
struct shrink_control *sc);
static struct shrinker nfsd_reply_cache_shrinker = {
.scan_objects = nfsd_reply_cache_scan,
.count_objects = nfsd_reply_cache_count,
.seeks = 1,
};
/*
* locking for the reply cache:
* A cache entry is "single use" if c_state == RC_INPROG
* Otherwise, it when accessing _prev or _next, the lock must be held.
*/
static DEFINE_SPINLOCK(cache_lock);
static DECLARE_DELAYED_WORK(cache_cleaner, cache_cleaner_func);
/*
* Put a cap on the size of the DRC based on the amount of available
* low memory in the machine.
*
* 64MB: 8192
* 128MB: 11585
* 256MB: 16384
* 512MB: 23170
* 1GB: 32768
* 2GB: 46340
* 4GB: 65536
* 8GB: 92681
* 16GB: 131072
*
* ...with a hard cap of 256k entries. In the worst case, each entry will be
* ~1k, so the above numbers should give a rough max of the amount of memory
* used in k.
*/
static unsigned int
nfsd_cache_size_limit(void)
{
unsigned int limit;
unsigned long low_pages = totalram_pages - totalhigh_pages;
limit = (16 * int_sqrt(low_pages)) << (PAGE_SHIFT-10);
return min_t(unsigned int, limit, 256*1024);
}
/*
* Compute the number of hash buckets we need. Divide the max cachesize by
* the "target" max bucket size, and round up to next power of two.
*/
static unsigned int
nfsd_hashsize(unsigned int limit)
{
return roundup_pow_of_two(limit / TARGET_BUCKET_SIZE);
}
static struct svc_cacherep *
nfsd_reply_cache_alloc(void)
{
struct svc_cacherep *rp;
rp = kmem_cache_alloc(drc_slab, GFP_KERNEL);
if (rp) {
rp->c_state = RC_UNUSED;
rp->c_type = RC_NOCACHE;
INIT_LIST_HEAD(&rp->c_lru);
INIT_HLIST_NODE(&rp->c_hash);
}
return rp;
}
static void
nfsd_reply_cache_unhash(struct svc_cacherep *rp)
{
hlist_del_init(&rp->c_hash);
list_del_init(&rp->c_lru);
}
static void
nfsd_reply_cache_free_locked(struct svc_cacherep *rp)
{
if (rp->c_type == RC_REPLBUFF && rp->c_replvec.iov_base) {
drc_mem_usage -= rp->c_replvec.iov_len;
kfree(rp->c_replvec.iov_base);
}
if (!hlist_unhashed(&rp->c_hash))
hlist_del(&rp->c_hash);
list_del(&rp->c_lru);
--num_drc_entries;
drc_mem_usage -= sizeof(*rp);
kmem_cache_free(drc_slab, rp);
}
static void
nfsd_reply_cache_free(struct svc_cacherep *rp)
{
spin_lock(&cache_lock);
nfsd_reply_cache_free_locked(rp);
spin_unlock(&cache_lock);
}
int nfsd_reply_cache_init(void)
{
unsigned int hashsize;
INIT_LIST_HEAD(&lru_head);
max_drc_entries = nfsd_cache_size_limit();
num_drc_entries = 0;
hashsize = nfsd_hashsize(max_drc_entries);
maskbits = ilog2(hashsize);
register_shrinker(&nfsd_reply_cache_shrinker);
drc_slab = kmem_cache_create("nfsd_drc", sizeof(struct svc_cacherep),
0, 0, NULL);
if (!drc_slab)
goto out_nomem;
cache_hash = kcalloc(hashsize, sizeof(struct hlist_head), GFP_KERNEL);
if (!cache_hash)
goto out_nomem;
return 0;
out_nomem:
printk(KERN_ERR "nfsd: failed to allocate reply cache\n");
nfsd_reply_cache_shutdown();
return -ENOMEM;
}
void nfsd_reply_cache_shutdown(void)
{
struct svc_cacherep *rp;
unregister_shrinker(&nfsd_reply_cache_shrinker);
cancel_delayed_work_sync(&cache_cleaner);
while (!list_empty(&lru_head)) {
rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
nfsd_reply_cache_free_locked(rp);
}
kfree (cache_hash);
cache_hash = NULL;
if (drc_slab) {
kmem_cache_destroy(drc_slab);
drc_slab = NULL;
}
}
/*
* Move cache entry to end of LRU list, and queue the cleaner to run if it's
* not already scheduled.
*/
static void
lru_put_end(struct svc_cacherep *rp)
{
rp->c_timestamp = jiffies;
list_move_tail(&rp->c_lru, &lru_head);
schedule_delayed_work(&cache_cleaner, RC_EXPIRE);
}
/*
* Move a cache entry from one hash list to another
*/
static void
hash_refile(struct svc_cacherep *rp)
{
hlist_del_init(&rp->c_hash);
hlist_add_head(&rp->c_hash, cache_hash + hash_32(rp->c_xid, maskbits));
}
static inline bool
nfsd_cache_entry_expired(struct svc_cacherep *rp)
{
return rp->c_state != RC_INPROG &&
time_after(jiffies, rp->c_timestamp + RC_EXPIRE);
}
/*
* Walk the LRU list and prune off entries that are older than RC_EXPIRE.
* Also prune the oldest ones when the total exceeds the max number of entries.
*/
static long
prune_cache_entries(void)
{
struct svc_cacherep *rp, *tmp;
long freed = 0;
list_for_each_entry_safe(rp, tmp, &lru_head, c_lru) {
if (!nfsd_cache_entry_expired(rp) &&
num_drc_entries <= max_drc_entries)
break;
nfsd_reply_cache_free_locked(rp);
freed++;
}
/*
* Conditionally rearm the job. If we cleaned out the list, then
* cancel any pending run (since there won't be any work to do).
* Otherwise, we rearm the job or modify the existing one to run in
* RC_EXPIRE since we just ran the pruner.
*/
if (list_empty(&lru_head))
cancel_delayed_work(&cache_cleaner);
else
mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE);
return freed;
}
static void
cache_cleaner_func(struct work_struct *unused)
{
spin_lock(&cache_lock);
prune_cache_entries();
spin_unlock(&cache_lock);
}
static unsigned long
nfsd_reply_cache_count(struct shrinker *shrink, struct shrink_control *sc)
{
unsigned long num;
spin_lock(&cache_lock);
num = num_drc_entries;
spin_unlock(&cache_lock);
return num;
}
static unsigned long
nfsd_reply_cache_scan(struct shrinker *shrink, struct shrink_control *sc)
{
unsigned long freed;
spin_lock(&cache_lock);
freed = prune_cache_entries();
spin_unlock(&cache_lock);
return freed;
}
/*
* Walk an xdr_buf and get a CRC for at most the first RC_CSUMLEN bytes
*/
static __wsum
nfsd_cache_csum(struct svc_rqst *rqstp)
{
int idx;
unsigned int base;
__wsum csum;
struct xdr_buf *buf = &rqstp->rq_arg;
const unsigned char *p = buf->head[0].iov_base;
size_t csum_len = min_t(size_t, buf->head[0].iov_len + buf->page_len,
RC_CSUMLEN);
size_t len = min(buf->head[0].iov_len, csum_len);
/* rq_arg.head first */
csum = csum_partial(p, len, 0);
csum_len -= len;
/* Continue into page array */
idx = buf->page_base / PAGE_SIZE;
base = buf->page_base & ~PAGE_MASK;
while (csum_len) {
p = page_address(buf->pages[idx]) + base;
len = min_t(size_t, PAGE_SIZE - base, csum_len);
csum = csum_partial(p, len, csum);
csum_len -= len;
base = 0;
++idx;
}
return csum;
}
static bool
nfsd_cache_match(struct svc_rqst *rqstp, __wsum csum, struct svc_cacherep *rp)
{
/* Check RPC header info first */
if (rqstp->rq_xid != rp->c_xid || rqstp->rq_proc != rp->c_proc ||
rqstp->rq_prot != rp->c_prot || rqstp->rq_vers != rp->c_vers ||
rqstp->rq_arg.len != rp->c_len ||
!rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) ||
rpc_get_port(svc_addr(rqstp)) != rpc_get_port((struct sockaddr *)&rp->c_addr))
return false;
/* compare checksum of NFS data */
if (csum != rp->c_csum) {
++payload_misses;
return false;
}
return true;
}
/*
* Search the request hash for an entry that matches the given rqstp.
* Must be called with cache_lock held. Returns the found entry or
* NULL on failure.
*/
static struct svc_cacherep *
nfsd_cache_search(struct svc_rqst *rqstp, __wsum csum)
{
struct svc_cacherep *rp, *ret = NULL;
struct hlist_head *rh;
unsigned int entries = 0;
rh = &cache_hash[hash_32(rqstp->rq_xid, maskbits)];
hlist_for_each_entry(rp, rh, c_hash) {
++entries;
if (nfsd_cache_match(rqstp, csum, rp)) {
ret = rp;
break;
}
}
/* tally hash chain length stats */
if (entries > longest_chain) {
longest_chain = entries;
longest_chain_cachesize = num_drc_entries;
} else if (entries == longest_chain) {
/* prefer to keep the smallest cachesize possible here */
longest_chain_cachesize = min(longest_chain_cachesize,
num_drc_entries);
}
return ret;
}
/*
* Try to find an entry matching the current call in the cache. When none
* is found, we try to grab the oldest expired entry off the LRU list. If
* a suitable one isn't there, then drop the cache_lock and allocate a
* new one, then search again in case one got inserted while this thread
* didn't hold the lock.
*/
int
nfsd_cache_lookup(struct svc_rqst *rqstp)
{
struct svc_cacherep *rp, *found;
__be32 xid = rqstp->rq_xid;
u32 proto = rqstp->rq_prot,
vers = rqstp->rq_vers,
proc = rqstp->rq_proc;
__wsum csum;
unsigned long age;
int type = rqstp->rq_cachetype;
int rtn = RC_DOIT;
rqstp->rq_cacherep = NULL;
if (type == RC_NOCACHE) {
nfsdstats.rcnocache++;
return rtn;
}
csum = nfsd_cache_csum(rqstp);
/*
* Since the common case is a cache miss followed by an insert,
* preallocate an entry. First, try to reuse the first entry on the LRU
* if it works, then go ahead and prune the LRU list.
*/
spin_lock(&cache_lock);
if (!list_empty(&lru_head)) {
rp = list_first_entry(&lru_head, struct svc_cacherep, c_lru);
if (nfsd_cache_entry_expired(rp) ||
num_drc_entries >= max_drc_entries) {
nfsd_reply_cache_unhash(rp);
prune_cache_entries();
goto search_cache;
}
}
/* No expired ones available, allocate a new one. */
spin_unlock(&cache_lock);
rp = nfsd_reply_cache_alloc();
spin_lock(&cache_lock);
if (likely(rp)) {
++num_drc_entries;
drc_mem_usage += sizeof(*rp);
}
search_cache:
found = nfsd_cache_search(rqstp, csum);
if (found) {
if (likely(rp))
nfsd_reply_cache_free_locked(rp);
rp = found;
goto found_entry;
}
if (!rp) {
dprintk("nfsd: unable to allocate DRC entry!\n");
goto out;
}
/*
* We're keeping the one we just allocated. Are we now over the
* limit? Prune one off the tip of the LRU in trade for the one we
* just allocated if so.
*/
if (num_drc_entries >= max_drc_entries)
nfsd_reply_cache_free_locked(list_first_entry(&lru_head,
struct svc_cacherep, c_lru));
nfsdstats.rcmisses++;
rqstp->rq_cacherep = rp;
rp->c_state = RC_INPROG;
rp->c_xid = xid;
rp->c_proc = proc;
rpc_copy_addr((struct sockaddr *)&rp->c_addr, svc_addr(rqstp));
rpc_set_port((struct sockaddr *)&rp->c_addr, rpc_get_port(svc_addr(rqstp)));
rp->c_prot = proto;
rp->c_vers = vers;
rp->c_len = rqstp->rq_arg.len;
rp->c_csum = csum;
hash_refile(rp);
lru_put_end(rp);
/* release any buffer */
if (rp->c_type == RC_REPLBUFF) {
drc_mem_usage -= rp->c_replvec.iov_len;
kfree(rp->c_replvec.iov_base);
rp->c_replvec.iov_base = NULL;
}
rp->c_type = RC_NOCACHE;
out:
spin_unlock(&cache_lock);
return rtn;
found_entry:
nfsdstats.rchits++;
/* We found a matching entry which is either in progress or done. */
age = jiffies - rp->c_timestamp;
lru_put_end(rp);
rtn = RC_DROPIT;
/* Request being processed or excessive rexmits */
if (rp->c_state == RC_INPROG || age < RC_DELAY)
goto out;
/* From the hall of fame of impractical attacks:
* Is this a user who tries to snoop on the cache? */
rtn = RC_DOIT;
if (!rqstp->rq_secure && rp->c_secure)
goto out;
/* Compose RPC reply header */
switch (rp->c_type) {
case RC_NOCACHE:
break;
case RC_REPLSTAT:
svc_putu32(&rqstp->rq_res.head[0], rp->c_replstat);
rtn = RC_REPLY;
break;
case RC_REPLBUFF:
if (!nfsd_cache_append(rqstp, &rp->c_replvec))
goto out; /* should not happen */
rtn = RC_REPLY;
break;
default:
printk(KERN_WARNING "nfsd: bad repcache type %d\n", rp->c_type);
nfsd_reply_cache_free_locked(rp);
}
goto out;
}
/*
* Update a cache entry. This is called from nfsd_dispatch when
* the procedure has been executed and the complete reply is in
* rqstp->rq_res.
*
* We're copying around data here rather than swapping buffers because
* the toplevel loop requires max-sized buffers, which would be a waste
* of memory for a cache with a max reply size of 100 bytes (diropokres).
*
* If we should start to use different types of cache entries tailored
* specifically for attrstat and fh's, we may save even more space.
*
* Also note that a cachetype of RC_NOCACHE can legally be passed when
* nfsd failed to encode a reply that otherwise would have been cached.
* In this case, nfsd_cache_update is called with statp == NULL.
*/
void
nfsd_cache_update(struct svc_rqst *rqstp, int cachetype, __be32 *statp)
{
struct svc_cacherep *rp = rqstp->rq_cacherep;
struct kvec *resv = &rqstp->rq_res.head[0], *cachv;
int len;
size_t bufsize = 0;
if (!rp)
return;
len = resv->iov_len - ((char*)statp - (char*)resv->iov_base);
len >>= 2;
/* Don't cache excessive amounts of data and XDR failures */
if (!statp || len > (256 >> 2)) {
nfsd_reply_cache_free(rp);
return;
}
switch (cachetype) {
case RC_REPLSTAT:
if (len != 1)
printk("nfsd: RC_REPLSTAT/reply len %d!\n",len);
rp->c_replstat = *statp;
break;
case RC_REPLBUFF:
cachv = &rp->c_replvec;
bufsize = len << 2;
cachv->iov_base = kmalloc(bufsize, GFP_KERNEL);
if (!cachv->iov_base) {
nfsd_reply_cache_free(rp);
return;
}
cachv->iov_len = bufsize;
memcpy(cachv->iov_base, statp, bufsize);
break;
case RC_NOCACHE:
nfsd_reply_cache_free(rp);
return;
}
spin_lock(&cache_lock);
drc_mem_usage += bufsize;
lru_put_end(rp);
rp->c_secure = rqstp->rq_secure;
rp->c_type = cachetype;
rp->c_state = RC_DONE;
spin_unlock(&cache_lock);
return;
}
/*
* Copy cached reply to current reply buffer. Should always fit.
* FIXME as reply is in a page, we should just attach the page, and
* keep a refcount....
*/
static int
nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *data)
{
struct kvec *vec = &rqstp->rq_res.head[0];
if (vec->iov_len + data->iov_len > PAGE_SIZE) {
printk(KERN_WARNING "nfsd: cached reply too large (%Zd).\n",
data->iov_len);
return 0;
}
memcpy((char*)vec->iov_base + vec->iov_len, data->iov_base, data->iov_len);
vec->iov_len += data->iov_len;
return 1;
}
/*
* Note that fields may be added, removed or reordered in the future. Programs
* scraping this file for info should test the labels to ensure they're
* getting the correct field.
*/
static int nfsd_reply_cache_stats_show(struct seq_file *m, void *v)
{
spin_lock(&cache_lock);
seq_printf(m, "max entries: %u\n", max_drc_entries);
seq_printf(m, "num entries: %u\n", num_drc_entries);
seq_printf(m, "hash buckets: %u\n", 1 << maskbits);
seq_printf(m, "mem usage: %u\n", drc_mem_usage);
seq_printf(m, "cache hits: %u\n", nfsdstats.rchits);
seq_printf(m, "cache misses: %u\n", nfsdstats.rcmisses);
seq_printf(m, "not cached: %u\n", nfsdstats.rcnocache);
seq_printf(m, "payload misses: %u\n", payload_misses);
seq_printf(m, "longest chain len: %u\n", longest_chain);
seq_printf(m, "cachesize at longest: %u\n", longest_chain_cachesize);
spin_unlock(&cache_lock);
return 0;
}
int nfsd_reply_cache_stats_open(struct inode *inode, struct file *file)
{
return single_open(file, nfsd_reply_cache_stats_show, NULL);
}