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fs, nfs: convert nfs4_lock_state.ls_count from atomic_t to refcount_t 

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_lock_state.ls_count  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: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
Elena Reshetova 2017-10-20 12:53:36 +03:00 committed by Anna Schumaker
parent 0896cade12
commit 194bc1f481
3 changed files with 8 additions and 8 deletions
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2
fs/nfs/nfs4_fs.h
View File

@ -144,7 +144,7 @@ struct nfs4_lock_state {
unsigned long ls_flags;
struct nfs_seqid_counter ls_seqid;
nfs4_stateid ls_stateid;
atomic_t ls_count;
refcount_t ls_count;
fl_owner_t ls_owner;
};

6
fs/nfs/nfs4proc.c
View File

@ -2562,7 +2562,7 @@ static int nfs41_check_expired_locks(struct nfs4_state *state)
if (test_bit(NFS_LOCK_INITIALIZED, &lsp->ls_flags)) {
struct rpc_cred *cred = lsp->ls_state->owner->so_cred;
atomic_inc(&lsp->ls_count);
refcount_inc(&lsp->ls_count);
spin_unlock(&state->state_lock);
nfs4_put_lock_state(prev);
@ -5923,7 +5923,7 @@ static struct nfs4_unlockdata *nfs4_alloc_unlockdata(struct file_lock *fl,
p->arg.seqid = seqid;
p->res.seqid = seqid;
p->lsp = lsp;
atomic_inc(&lsp->ls_count);
refcount_inc(&lsp->ls_count);
/* Ensure we don't close file until we're done freeing locks! */
p->ctx = get_nfs_open_context(ctx);
p->l_ctx = nfs_get_lock_context(ctx);
@ -6139,7 +6139,7 @@ static struct nfs4_lockdata *nfs4_alloc_lockdata(struct file_lock *fl,
p->res.lock_seqid = p->arg.lock_seqid;
p->lsp = lsp;
p->server = server;
atomic_inc(&lsp->ls_count);
refcount_inc(&lsp->ls_count);
p->ctx = get_nfs_open_context(ctx);
memcpy(&p->fl, fl, sizeof(p->fl));
return p;

8
fs/nfs/nfs4state.c
View File

@ -825,7 +825,7 @@ __nfs4_find_lock_state(struct nfs4_state *state,
ret = pos;
}
if (ret)
atomic_inc(&ret->ls_count);
refcount_inc(&ret->ls_count);
return ret;
}
@ -843,7 +843,7 @@ static struct nfs4_lock_state *nfs4_alloc_lock_state(struct nfs4_state *state, f
if (lsp == NULL)
return NULL;
nfs4_init_seqid_counter(&lsp->ls_seqid);
atomic_set(&lsp->ls_count, 1);
refcount_set(&lsp->ls_count, 1);
lsp->ls_state = state;
lsp->ls_owner = fl_owner;
lsp->ls_seqid.owner_id = ida_simple_get(&server->lockowner_id, 0, 0, GFP_NOFS);
@ -907,7 +907,7 @@ void nfs4_put_lock_state(struct nfs4_lock_state *lsp)
if (lsp == NULL)
return;
state = lsp->ls_state;
if (!atomic_dec_and_lock(&lsp->ls_count, &state->state_lock))
if (!refcount_dec_and_lock(&lsp->ls_count, &state->state_lock))
return;
list_del(&lsp->ls_locks);
if (list_empty(&state->lock_states))
@ -927,7 +927,7 @@ static void nfs4_fl_copy_lock(struct file_lock *dst, struct file_lock *src)
struct nfs4_lock_state *lsp = src->fl_u.nfs4_fl.owner;
dst->fl_u.nfs4_fl.owner = lsp;
atomic_inc(&lsp->ls_count);
refcount_inc(&lsp->ls_count);
}
static void nfs4_fl_release_lock(struct file_lock *fl)