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Subject[PATCH 11/13] vfs: protect i_nlink
Date
From: Miklos Szeredi <mszeredi@suse.cz>

Prevent direct modification of i_nlink by making it const and adding a
non-const __i_nlink alias.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
fs/inode.c | 2 +-
include/linux/fs.h | 20 +++++++++++++++-----
2 files changed, 16 insertions(+), 6 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index ec79246..e2d3633 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -142,7 +142,7 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
atomic_set(&inode->i_count, 1);
inode->i_op = &empty_iops;
inode->i_fop = &empty_fops;
- inode->i_nlink = 1;
+ inode->__i_nlink = 1;
inode->i_opflags = 0;
inode->i_uid = 0;
inode->i_gid = 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 28f4998..7813404 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -767,7 +767,17 @@ struct inode {

/* Stat data, not accessed from path walking */
unsigned long i_ino;
- unsigned int i_nlink;
+ /*
+ * Filesystems may only read i_nlink directly. They shall use the
+ * following functions for modification:
+ *
+ * (set|clear|inc|drop)_nlink
+ * inode_(inc|dec)_link_count
+ */
+ union {
+ const unsigned int i_nlink;
+ unsigned int __i_nlink;
+ };
dev_t i_rdev;
loff_t i_size;
struct timespec i_atime;
@@ -1757,7 +1767,7 @@ static inline void mark_inode_dirty_sync(struct inode *inode)
*/
static inline void set_nlink(struct inode *inode, unsigned int nlink)
{
- inode->i_nlink = nlink;
+ inode->__i_nlink = nlink;
}

/**
@@ -1770,7 +1780,7 @@ static inline void set_nlink(struct inode *inode, unsigned int nlink)
*/
static inline void inc_nlink(struct inode *inode)
{
- inode->i_nlink++;
+ inode->__i_nlink++;
}

static inline void inode_inc_link_count(struct inode *inode)
@@ -1792,7 +1802,7 @@ static inline void inode_inc_link_count(struct inode *inode)
*/
static inline void drop_nlink(struct inode *inode)
{
- inode->i_nlink--;
+ inode->__i_nlink--;
}

/**
@@ -1805,7 +1815,7 @@ static inline void drop_nlink(struct inode *inode)
*/
static inline void clear_nlink(struct inode *inode)
{
- inode->i_nlink = 0;
+ inode->__i_nlink = 0;
}

static inline void inode_dec_link_count(struct inode *inode)
--
1.7.3.4


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