From: Al Viro Date: Wed, 8 Jun 2016 01:26:55 +0000 (-0400) Subject: fix d_walk()/non-delayed __d_free() race X-Git-Tag: v3.2.82~50 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=37f4f9e677576c8f8add9f43844c6c468caf8252 fix d_walk()/non-delayed __d_free() race commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 upstream. 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. Signed-off-by: Al Viro [bwh: Backported to 3.2: - Adjust context - Also set the flag in __d_materialise_dentry())] Signed-off-by: Ben Hutchings --- diff --git a/fs/dcache.c b/fs/dcache.c index 46265f58b5b8..01c68ae3129c 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -1261,7 +1261,7 @@ 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 @@ -2011,7 +2011,6 @@ 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); } @@ -2195,6 +2194,7 @@ static void __d_move(struct dentry * dentry, struct dentry * target) /* ... and switch the parents */ if (IS_ROOT(dentry)) { + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_parent = target->d_parent; target->d_parent = target; INIT_LIST_HEAD(&target->d_child); @@ -2311,6 +2311,7 @@ static void __d_materialise_dentry(struct dentry *dentry, struct dentry *anon) switch_names(dentry, anon); swap(dentry->d_name.hash, anon->d_name.hash); + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_parent = (aparent == anon) ? dentry : aparent; list_del(&dentry->d_child); if (!IS_ROOT(dentry))