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Commit d4f0284a authored by Elena Reshetova's avatar Elena Reshetova Committed by Linus Torvalds
Browse files

fs, nilfs: convert nilfs_root.count from atomic_t to refcount_t 

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.

Link: http://lkml.kernel.org/r/1509367935-3086-3-git-send-email-konishi.ryusuke@lab.ntt.co.jp


Signed-off-by: default avatarElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: default avatarRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Suggested-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarDavid Windsor <dwindsor@gmail.com>
Reviewed-by: default avatarHans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 31ccb1f7

fs/nilfs2/the_nilfs.c

+4 −4
Original line number Diff line number Diff line
@@ -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);

fs/nilfs2/the_nilfs.h

+3 −2
Original line number Diff line number Diff line
@@ -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)