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

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: default avatarElena Reshetova <>
Signed-off-by: default avatarRyusuke Konishi <>
Suggested-by: default avatarKees Cook <>
Reviewed-by: default avatarDavid Windsor <>
Reviewed-by: default avatarHans Liljestrand <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 31ccb1f7
......@@ -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 {
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 {
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;
......@@ -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)
static inline int nilfs_valid_fs(struct the_nilfs *nilfs)
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