> 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@xxxxxxxxxxxx>
> > Reviewed-by: David Windsor <dwindsor@xxxxxxxxx>
> > Reviewed-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
> > Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
>
> Applied, thank you.
Thank you very much!
Best Regards,
Elena.
>
> 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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