There is a place in overlayfs where it may touch a lower-layer inode during
RCU-mode pathwalk. In this situation the combination of d_backing_inode() and
ACCESS_ONCE() does not compile, so institute and use a d_backing_inode_rcu()
function that combines these.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---
fs/overlayfs/inode.c | 2 +-
include/linux/dcache.h | 18 ++++++++++++++++++
2 files changed, 19 insertions(+), 1 deletion(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index ead6a7a6fe9d..7e3a7e3ff095 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -99,7 +99,7 @@ int ovl_permission(struct inode *inode, int mask)
realdentry = ovl_entry_real(oe, &is_upper);
/* Careful in RCU walk mode */
- realinode = ACCESS_ONCE(realdentry->d_inode);
+ realinode = d_backing_inode_rcu(realdentry);
if (!realinode) {
WARN_ON(!(mask & MAY_NOT_BLOCK));
err = -ENOENT;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index df334cbacc6d..50004f2429a1 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -562,6 +562,24 @@ static inline struct inode *d_backing_inode(const struct dentry *upper)
}
/**
+ * d_backing_inode_rcu - Get upper or lower inode we should be using with ACCESS_ONCE()
+ * @upper: The upper layer
+ *
+ * This is the helper that should be used to get at the inode that will be used
+ * if this dentry were to be opened as a file. The inode may be on the upper
+ * dentry or it may be on a lower dentry pinned by the upper. Further, the
+ * upper dentry might not have an inode set.
+ *
+ * Normal filesystems should not use this to access their own inodes.
+ */
+static inline struct inode *d_backing_inode_rcu(const struct dentry *upper)
+{
+ struct inode *inode = ACCESS_ONCE(upper->d_inode);
+
+ return inode;
+}
+
+/**
* d_backing_dentry - Get upper or lower dentry we should be using
* @upper: The upper layer
*
--
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