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fs, nfsd: convert nfs4_cntl_odstate.co_odcount from atomic_t to refcount_t

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atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable nfs4_cntl_odstate.co_odcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Elena Reshetova 2017-10-20 12:53:29 +03:00 committed by J. Bruce Fields
parent a15dfcd529
commit cff7cb2ece
2 changed files with 4 additions and 4 deletions
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6
fs/nfsd/nfs4state.c
View file

@ -568,7 +568,7 @@ alloc_clnt_odstate(struct nfs4_client *clp)
co = kmem_cache_zalloc(odstate_slab, GFP_KERNEL);
if (co) {
co->co_client = clp;
atomic_set(&co->co_odcount, 1);
refcount_set(&co->co_odcount, 1);
}
return co;
}
@ -586,7 +586,7 @@ static inline void
get_clnt_odstate(struct nfs4_clnt_odstate *co)
{
if (co)
atomic_inc(&co->co_odcount);
refcount_inc(&co->co_odcount);
}
static void
@ -598,7 +598,7 @@ put_clnt_odstate(struct nfs4_clnt_odstate *co)
return;
fp = co->co_file;
if (atomic_dec_and_lock(&co->co_odcount, &fp->fi_lock)) {
if (refcount_dec_and_lock(&co->co_odcount, &fp->fi_lock)) {
list_del(&co->co_perfile);
spin_unlock(&fp->fi_lock);

2
fs/nfsd/state.h
View file

@ -468,7 +468,7 @@ struct nfs4_clnt_odstate {
struct nfs4_client *co_client;
struct nfs4_file *co_file;
struct list_head co_perfile;
atomic_t co_odcount;
refcount_t co_odcount;
};
/*