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@xxxxxxxxxxxx>
Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
---
fs/nfsd/nfs4state.c | 6 +++---
fs/nfsd/state.h | 2 +-
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index d356b87..fb61d79 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -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);
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index f927aa4..58eb5f4 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -466,7 +466,7 @@ 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;
};
/*
--
2.7.4
--
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