Messages in this thread Patch in this message | | | From | Elena Reshetova <> | Subject | [PATCH 2/5] fs, xfs: convert xfs_efi_log_item.efi_refcount from atomic_t to refcount_t | Date | Fri, 20 Oct 2017 14:07:55 +0300 |
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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 xfs_efi_log_item.efi_refcount 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> --- fs/xfs/xfs_extfree_item.c | 6 +++--- fs/xfs/xfs_extfree_item.h | 2 +- 2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c index 44f8c54..dfe2bcb 100644 --- a/fs/xfs/xfs_extfree_item.c +++ b/fs/xfs/xfs_extfree_item.c @@ -220,7 +220,7 @@ xfs_efi_init( efip->efi_format.efi_nextents = nextents; efip->efi_format.efi_id = (uintptr_t)(void *)efip; atomic_set(&efip->efi_next_extent, 0); - atomic_set(&efip->efi_refcount, 2); + refcount_set(&efip->efi_refcount, 2); return efip; } @@ -290,8 +290,8 @@ void xfs_efi_release( struct xfs_efi_log_item *efip) { - ASSERT(atomic_read(&efip->efi_refcount) > 0); - if (atomic_dec_and_test(&efip->efi_refcount)) { + ASSERT(refcount_read(&efip->efi_refcount) > 0); + if (refcount_dec_and_test(&efip->efi_refcount)) { xfs_trans_ail_remove(&efip->efi_item, SHUTDOWN_LOG_IO_ERROR); xfs_efi_item_free(efip); } diff --git a/fs/xfs/xfs_extfree_item.h b/fs/xfs/xfs_extfree_item.h index a32c794..fadf736 100644 --- a/fs/xfs/xfs_extfree_item.h +++ b/fs/xfs/xfs_extfree_item.h @@ -64,7 +64,7 @@ struct kmem_zone; */ typedef struct xfs_efi_log_item { xfs_log_item_t efi_item; - atomic_t efi_refcount; + refcount_t efi_refcount; atomic_t efi_next_extent; unsigned long efi_flags; /* misc flags */ xfs_efi_log_format_t efi_format; -- 2.7.4
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