fix d_walk()/non-delayed __d_free() race (3d56c25e) · Commits · 戴 / test

Ascend-to-parent logics in d_walk() depends on all encountered child dentries not getting freed without an RCU delay. Unfortunately, in quite a few cases it is not true, with hard-to-hit oopsable race as the result. Fortunately, the fix is simiple; right now the rule is "if it ever been hashed, freeing must be delayed" and changing it to "if it ever had a parent, freeing must be delayed" closes that hole and covers all cases the old rule used to cover. Moreover, pipes and sockets remain _not_ covered, so we do not introduce RCU delay in the cases which are the reason for having that delay conditional in the first place. Cc: stable@vger.kernel.org # v3.2+ (and watch out for __d_materialise_dentry()) Signed-off-by:

Al Viro <viro@zeniv.linux.org.uk>

fs/dcache.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1636,7 +1636,7 @@ struct dentry d_alloc(struct dentry parent, const struct qstr *name)
		struct dentry *dentry = __d_alloc(parent->d_sb, name);
		if (!dentry)
		return NULL;

		dentry->d_flags \|= DCACHE_RCUACCESS;
		spin_lock(&parent->d_lock);
		/*
		* don't need child lock because it is not subject
		@@ -2358,7 +2358,6 @@ static void __d_rehash(struct dentry * entry, struct hlist_bl_head *b)
		{
		BUG_ON(!d_unhashed(entry));
		hlist_bl_lock(b);
		entry->d_flags \|= DCACHE_RCUACCESS;
		hlist_bl_add_head_rcu(&entry->d_hash, b);
		hlist_bl_unlock(b);
		}
		@@ -2843,6 +2842,7 @@ static void __d_move(struct dentry dentry, struct dentry target,
		/* ... and switch them in the tree */
		if (IS_ROOT(dentry)) {
		/* splicing a tree */
		dentry->d_flags \|= DCACHE_RCUACCESS;
		dentry->d_parent = target->d_parent;
		target->d_parent = target;
		list_del_init(&target->d_child);

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