[rh7,05/14] dcache: close d_move race in d_splice_alias

Submitted by Andrey Ryabinin on June 10, 2019, 3:13 p.m.


Message ID 20190610151400.12820-5-aryabinin@virtuozzo.com
State New
Series "Series without cover letter"
Headers show

Commit Message

Andrey Ryabinin June 10, 2019, 3:13 p.m.
From: "J. Bruce Fields" <bfields@redhat.com>

d_splice_alias will d_move an IS_ROOT() directory dentry into place if
one exists.  This should be safe as long as the dentry remains IS_ROOT,
but I can't see what guarantees that: once we drop the i_lock all we
hold here is the i_mutex on an unrelated parent directory.

Instead copy the logic of d_materialise_unique.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
(cherry picked from commit 75a2352d0110960aeee1a28ddc09a55f97c99100)
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
 fs/dcache.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

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diff --git a/fs/dcache.c b/fs/dcache.c
index 3f6a128e6c20..59760ae9b3fa 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2815,9 +2815,14 @@  struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
 		new = __d_find_alias(inode, 1);
 		if (new) {
 			BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
+			write_seqlock(&rename_lock);
+			__d_materialise_dentry(dentry, new);
+			write_sequnlock(&rename_lock);
+			__d_drop(new);
+			_d_rehash(new);
+			spin_unlock(&new->d_lock);
 			security_d_instantiate(new, inode);
-			d_move(new, dentry);
 		} else {
 			/* already taking inode->i_lock, so d_add() by hand */