On Wed, Mar 01, 2017 at 10:47:39AM +0200, Elena Reshetova wrote:
> refcount_t type and corresponding API should be
> used instead of atomic_t when the variable is used as
> a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free
> situations.
>
> Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
> Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
> ---
> fs/xfs/xfs_refcount_item.c | 4 ++--
> fs/xfs/xfs_refcount_item.h | 4 +++-
> 2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xfs/xfs_refcount_item.c b/fs/xfs/xfs_refcount_item.c
> index 6e4c744..61bc570 100644
> --- a/fs/xfs/xfs_refcount_item.c
> +++ b/fs/xfs/xfs_refcount_item.c
> @@ -205,7 +205,7 @@ xfs_cui_init(
> cuip->cui_format.cui_nextents = nextents;
> cuip->cui_format.cui_id = (uintptr_t)(void *)cuip;
> atomic_set(&cuip->cui_next_extent, 0);
> - atomic_set(&cuip->cui_refcount, 2);
> + refcount_set(&cuip->cui_refcount, 2);
I'm assuming the refcount design is ok with the log item refcounts
starting at 2 and marching down to zero? The code seems to be
fine with it; I just want to make sure everyone's ok with supporting
this use case.
> return cuip;
> }
> @@ -221,7 +221,7 @@ void
> xfs_cui_release(
> struct xfs_cui_log_item *cuip)
> {
> - if (atomic_dec_and_test(&cuip->cui_refcount)) {
> + if (refcount_dec_and_test(&cuip->cui_refcount)) {
I suppose it's useful to have refcount_dec_and_test complain loudly if
we ever have a dangling pointer... Friday I was chasing a possible
use-after-free of the EFI items in generic/388.
> xfs_trans_ail_remove(&cuip->cui_item, SHUTDOWN_LOG_IO_ERROR);
> xfs_cui_item_free(cuip);
> }
> diff --git a/fs/xfs/xfs_refcount_item.h b/fs/xfs/xfs_refcount_item.h
> index 5b74ddd..7f23ff8 100644
> --- a/fs/xfs/xfs_refcount_item.h
> +++ b/fs/xfs/xfs_refcount_item.h
> @@ -20,6 +20,8 @@
> #ifndef __XFS_REFCOUNT_ITEM_H__
> #define __XFS_REFCOUNT_ITEM_H__
>
> +#include <linux/refcount.h>
I still think this include should go in xfs_linux.h, the same as most of
the other linux/*.h includes in XFS.
--D
> +
> /*
> * There are (currently) two pairs of refcount btree redo item types:
> * increase and decrease. The log items for these are CUI (refcount
> @@ -63,7 +65,7 @@ struct kmem_zone;
> */
> struct xfs_cui_log_item {
> struct xfs_log_item cui_item;
> - atomic_t cui_refcount;
> + refcount_t cui_refcount;
> atomic_t cui_next_extent;
> unsigned long cui_flags; /* misc flags */
> struct xfs_cui_log_format cui_format;
> --
> 2.7.4
>
> --
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