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 pnfs_layout_hdr.plh_refcount is used as pure reference counter. Convert it to refcount_t and fix up the operations. Suggested-by: Kees Cook <keesc...@chromium.org> Reviewed-by: David Windsor <dwind...@gmail.com> Reviewed-by: Hans Liljestrand <ishkam...@gmail.com> Signed-off-by: Elena Reshetova <elena.reshet...@intel.com> --- fs/nfs/pnfs.c | 12 ++++++------ fs/nfs/pnfs.h | 2 +- 2 files changed, 7 insertions(+), 7 deletions(-) diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c index 499bb71..4aab53b 100644 --- a/fs/nfs/pnfs.c +++ b/fs/nfs/pnfs.c @@ -251,7 +251,7 @@ EXPORT_SYMBOL_GPL(pnfs_unregister_layoutdriver); void pnfs_get_layout_hdr(struct pnfs_layout_hdr *lo) { - atomic_inc(&lo->plh_refcount); + refcount_inc(&lo->plh_refcount); } static struct pnfs_layout_hdr * @@ -296,7 +296,7 @@ pnfs_put_layout_hdr(struct pnfs_layout_hdr *lo) pnfs_layoutreturn_before_put_layout_hdr(lo); - if (atomic_dec_and_lock(&lo->plh_refcount, &inode->i_lock)) { + if (refcount_dec_and_lock(&lo->plh_refcount, &inode->i_lock)) { if (!list_empty(&lo->plh_segs)) WARN_ONCE(1, "NFS: BUG unfreed layout segments.\n"); pnfs_detach_layout_hdr(lo); @@ -395,14 +395,14 @@ pnfs_layout_set_fail_bit(struct pnfs_layout_hdr *lo, int fail_bit) { lo->plh_retry_timestamp = jiffies; if (!test_and_set_bit(fail_bit, &lo->plh_flags)) - atomic_inc(&lo->plh_refcount); + refcount_inc(&lo->plh_refcount); } static void pnfs_layout_clear_fail_bit(struct pnfs_layout_hdr *lo, int fail_bit) { if (test_and_clear_bit(fail_bit, &lo->plh_flags)) - atomic_dec(&lo->plh_refcount); + refcount_dec(&lo->plh_refcount); } static void @@ -472,7 +472,7 @@ pnfs_layout_remove_lseg(struct pnfs_layout_hdr *lo, WARN_ON(test_bit(NFS_LSEG_VALID, &lseg->pls_flags)); list_del_init(&lseg->pls_list); /* Matched by pnfs_get_layout_hdr in pnfs_layout_insert_lseg */ - atomic_dec(&lo->plh_refcount); + refcount_dec(&lo->plh_refcount); if (test_bit(NFS_LSEG_LAYOUTRETURN, &lseg->pls_flags)) return; if (list_empty(&lo->plh_segs) && @@ -1451,7 +1451,7 @@ alloc_init_layout_hdr(struct inode *ino, lo = pnfs_alloc_layout_hdr(ino, gfp_flags); if (!lo) return NULL; - atomic_set(&lo->plh_refcount, 1); + refcount_set(&lo->plh_refcount, 1); INIT_LIST_HEAD(&lo->plh_layouts); INIT_LIST_HEAD(&lo->plh_segs); INIT_LIST_HEAD(&lo->plh_return_segs); diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h index f0e98e1..78de7a2 100644 --- a/fs/nfs/pnfs.h +++ b/fs/nfs/pnfs.h @@ -180,7 +180,7 @@ struct pnfs_layoutdriver_type { }; struct pnfs_layout_hdr { - atomic_t plh_refcount; + refcount_t plh_refcount; atomic_t plh_outstanding; /* number of RPCs out */ struct list_head plh_layouts; /* other client layouts */ struct list_head plh_bulk_destroy; -- 2.7.4