Messages in this thread | | | Subject | Re: [PATCH] fs, nilfs: convert nilfs_root.count from atomic_t to refcount_t | From | Ryusuke Konishi <> | Date | Sat, 21 Oct 2017 03:46:24 +0900 |
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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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