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fs, nfs: convert nfs_lock_context.count from atomic_t to refcount_t

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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 nfs_lock_context.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>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
This commit is contained in:
Elena Reshetova 2017-10-20 12:53:37 +03:00 committed by Anna Schumaker
parent 194bc1f481
commit 2f62b5aa48
2 changed files with 8 additions and 7 deletions
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12
fs/nfs/inode.c
View File

@ -783,7 +783,7 @@ EXPORT_SYMBOL_GPL(nfs_getattr);
static void nfs_init_lock_context(struct nfs_lock_context *l_ctx)
{
atomic_set(&l_ctx->count, 1);
refcount_set(&l_ctx->count, 1);
l_ctx->lockowner = current->files;
INIT_LIST_HEAD(&l_ctx->list);
atomic_set(&l_ctx->io_count, 0);
@ -797,7 +797,7 @@ static struct nfs_lock_context *__nfs_find_lock_context(struct nfs_open_context
do {
if (pos->lockowner != current->files)
continue;
atomic_inc(&pos->count);
refcount_inc(&pos->count);
return pos;
} while ((pos = list_entry(pos->list.next, typeof(*pos), list)) != head);
return NULL;
@ -836,7 +836,7 @@ void nfs_put_lock_context(struct nfs_lock_context *l_ctx)
struct nfs_open_context *ctx = l_ctx->open_context;
struct inode *inode = d_inode(ctx->dentry);
if (!atomic_dec_and_lock(&l_ctx->count, &inode->i_lock))
if (!refcount_dec_and_lock(&l_ctx->count, &inode->i_lock))
return;
list_del(&l_ctx->list);
spin_unlock(&inode->i_lock);
@ -913,7 +913,7 @@ EXPORT_SYMBOL_GPL(alloc_nfs_open_context);
struct nfs_open_context *get_nfs_open_context(struct nfs_open_context *ctx)
{
if (ctx != NULL)
atomic_inc(&ctx->lock_context.count);
refcount_inc(&ctx->lock_context.count);
return ctx;
}
EXPORT_SYMBOL_GPL(get_nfs_open_context);
@ -924,11 +924,11 @@ static void __put_nfs_open_context(struct nfs_open_context *ctx, int is_sync)
struct super_block *sb = ctx->dentry->d_sb;
if (!list_empty(&ctx->list)) {
if (!atomic_dec_and_lock(&ctx->lock_context.count, &inode->i_lock))
if (!refcount_dec_and_lock(&ctx->lock_context.count, &inode->i_lock))
return;
list_del(&ctx->list);
spin_unlock(&inode->i_lock);
} else if (!atomic_dec_and_test(&ctx->lock_context.count))
} else if (!refcount_dec_and_test(&ctx->lock_context.count))
return;
if (inode != NULL)
NFS_PROTO(inode)->close_context(ctx, is_sync);

3
include/linux/nfs_fs.h
View File

@ -22,6 +22,7 @@
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/rbtree.h>
#include <linux/refcount.h>
#include <linux/rwsem.h>
#include <linux/wait.h>
@ -55,7 +56,7 @@ struct nfs_access_entry {
};
struct nfs_lock_context {
atomic_t count;
refcount_t count;
struct list_head list;
struct nfs_open_context *open_context;
fl_owner_t lockowner;