btrfs: convert scrub_block.refs from atomic_t to refcount_t

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@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index c9406bf302b86c4e6e9d29709fa59661f9f6a229..d2c35848e61da90e7bd8be043da1cba1a9cb6336 100644 (file)
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -112,7 +112,7 @@ struct scrub_block {
        struct scrub_page       *pagev[SCRUB_MAX_PAGES_PER_BLOCK];
        int                     page_count;
        atomic_t                outstanding_pages;
-       atomic_t                refs; /* free mem on transition to zero */
+       refcount_t              refs; /* free mem on transition to zero */
        struct scrub_ctx        *sctx;
        struct scrub_parity     *sparity;
        struct {
@@ -1998,12 +1998,12 @@ static int scrub_checksum_super(struct scrub_block *sblock)
 
 static void scrub_block_get(struct scrub_block *sblock)
 {
-       atomic_inc(&sblock->refs);
+       refcount_inc(&sblock->refs);
 }
 
 static void scrub_block_put(struct scrub_block *sblock)
 {
-       if (atomic_dec_and_test(&sblock->refs)) {
+       if (refcount_dec_and_test(&sblock->refs)) {
                int i;
 
                if (sblock->sparity)
@@ -2255,7 +2255,7 @@ static int scrub_pages(struct scrub_ctx *sctx, u64 logical, u64 len,
 
        /* one ref inside this function, plus one for each page added to
         * a bio later on */
-       atomic_set(&sblock->refs, 1);
+       refcount_set(&sblock->refs, 1);
        sblock->sctx = sctx;
        sblock->no_io_error_seen = 1;
 
@@ -2555,7 +2555,7 @@ static int scrub_pages_for_parity(struct scrub_parity *sparity,
 
        /* one ref inside this function, plus one for each page added to
         * a bio later on */
-       atomic_set(&sblock->refs, 1);
+       refcount_set(&sblock->refs, 1);
        sblock->sctx = sctx;
        sblock->no_io_error_seen = 1;
        sblock->sparity = sparity;