Commit 2f62b5aa authored by Elena Reshetova's avatar Elena Reshetova Committed by Anna Schumaker
Browse files

fs, nfs: convert nfs_lock_context.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 nfs_lock_context.count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

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 avatarElena Reshetova <elena.reshetova@intel.com>
Signed-off-by: default avatarAnna Schumaker <Anna.Schumaker@Netapp.com>
parent 194bc1f4

fs/nfs/inode.c

+6 −6
Original line number Diff line number Diff line
@@ -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);

include/linux/nfs_fs.h

+2 −1
Original line number Diff line number Diff line
@@ -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;

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