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SubjectRe: [PATCH] fs, nilfs: convert nilfs_root.count from atomic_t to refcount_t
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On 2017/10/20 19:51, Elena Reshetova wrote:
> 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 nilfs_root.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>

Applied, thank you.

Ryusuke Konishi

> ---
> fs/nilfs2/the_nilfs.c | 8 ++++----
> fs/nilfs2/the_nilfs.h | 5 +++--
> 2 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
> index 2dd75bf..afebb50 100644
> --- a/fs/nilfs2/the_nilfs.c
> +++ b/fs/nilfs2/the_nilfs.c
> @@ -737,7 +737,7 @@ struct nilfs_root *nilfs_lookup_root(struct the_nilfs *nilfs, __u64 cno)
> } else if (cno > root->cno) {
> n = n->rb_right;
> } else {
> - atomic_inc(&root->count);
> + refcount_inc(&root->count);
> spin_unlock(&nilfs->ns_cptree_lock);
> return root;
> }
> @@ -776,7 +776,7 @@ nilfs_find_or_create_root(struct the_nilfs *nilfs, __u64 cno)
> } else if (cno > root->cno) {
> p = &(*p)->rb_right;
> } else {
> - atomic_inc(&root->count);
> + refcount_inc(&root->count);
> spin_unlock(&nilfs->ns_cptree_lock);
> kfree(new);
> return root;
> @@ -786,7 +786,7 @@ nilfs_find_or_create_root(struct the_nilfs *nilfs, __u64 cno)
> new->cno = cno;
> new->ifile = NULL;
> new->nilfs = nilfs;
> - atomic_set(&new->count, 1);
> + refcount_set(&new->count, 1);
> atomic64_set(&new->inodes_count, 0);
> atomic64_set(&new->blocks_count, 0);
>
> @@ -806,7 +806,7 @@ nilfs_find_or_create_root(struct the_nilfs *nilfs, __u64 cno)
>
> void nilfs_put_root(struct nilfs_root *root)
> {
> - if (atomic_dec_and_test(&root->count)) {
> + if (refcount_dec_and_test(&root->count)) {
> struct the_nilfs *nilfs = root->nilfs;
>
> nilfs_sysfs_delete_snapshot_group(root);
> diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
> index b305c6f..883d732 100644
> --- a/fs/nilfs2/the_nilfs.h
> +++ b/fs/nilfs2/the_nilfs.h
> @@ -27,6 +27,7 @@
> #include <linux/blkdev.h>
> #include <linux/backing-dev.h>
> #include <linux/slab.h>
> +#include <linux/refcount.h>
>
> struct nilfs_sc_info;
> struct nilfs_sysfs_dev_subgroups;
> @@ -246,7 +247,7 @@ struct nilfs_root {
> __u64 cno;
> struct rb_node rb_node;
>
> - atomic_t count;
> + refcount_t count;
> struct the_nilfs *nilfs;
> struct inode *ifile;
>
> @@ -299,7 +300,7 @@ void nilfs_swap_super_block(struct the_nilfs *);
>
> static inline void nilfs_get_root(struct nilfs_root *root)
> {
> - atomic_inc(&root->count);
> + refcount_inc(&root->count);
> }
>
> static inline int nilfs_valid_fs(struct the_nilfs *nilfs)
>

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