From: Ondrej Mosnacek <omosnace@redhat.com>
To: selinux@vger.kernel.org, Paul Moore <paul@paul-moore.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>, linux-fsdevel@vger.kernel.org
Subject: [PATCH v2 3/4] dcache: introduce d_genocide_safe()
Date: Thu, 1 Aug 2019 16:02:42 +0200 [thread overview]
Message-ID: <20190801140243.24080-4-omosnace@redhat.com> (raw)
In-Reply-To: <20190801140243.24080-1-omosnace@redhat.com>
This patch adds a slightly modified variant of d_genocide() that works
safely on live (ramfs-like) trees. This function is needed for a safe
implementation of sel_remove_entries() in selinuxfs.
This new function differs from the original d_genocide in the following:
1. It locks the parent inode when traversing the dentries.
2. It first unhashes the dentry using __d_drop() before dropping the
refcount and marking the dentry.
3. It does its business in the leave callback so that each dentry is
unhashed after its children -- otherwise some dentries might never
get traversed when d_walk() is restarted internally.
The combination of (1.) and (2.) is needed to avoid racing with
dcache_readdir(), which relies on the assumption that any
simple_positive() child dentry will not turn negative without locking
the parent inode for writing.
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
---
fs/dcache.c | 32 ++++++++++++++++++++++++++++++++
include/linux/dcache.h | 1 +
2 files changed, 33 insertions(+)
diff --git a/fs/dcache.c b/fs/dcache.c
index 70afcb6e6892..f6d667120c1e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3142,6 +3142,38 @@ void d_genocide(struct dentry *parent)
EXPORT_SYMBOL(d_genocide);
+static enum d_walk_ret d_genocide_safe_enter(void *data, struct dentry *dentry)
+{
+ struct dentry *root = data;
+
+ if (dentry != root && !simple_positive(dentry))
+ return D_WALK_SKIP;
+
+ return D_WALK_CONTINUE;
+}
+
+static void d_genocide_safe_leave(void *data, struct dentry *dentry)
+{
+ struct dentry *root = data;
+
+ if (dentry != root) {
+ __d_drop(dentry);
+
+ if (!(dentry->d_flags & DCACHE_GENOCIDE)) {
+ dentry->d_flags |= DCACHE_GENOCIDE;
+ dentry->d_lockref.count--;
+ }
+ }
+}
+
+void d_genocide_safe(struct dentry *parent)
+{
+ d_walk(parent, true, parent, d_genocide_safe_enter,
+ d_genocide_safe_leave);
+}
+
+EXPORT_SYMBOL(d_genocide_safe);
+
void d_tmpfile(struct dentry *dentry, struct inode *inode)
{
inode_dec_link_count(inode);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 9451011ac014..6d787c26e901 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -253,6 +253,7 @@ extern struct dentry * d_make_root(struct inode *);
/* <clickety>-<click> the ramfs-type tree */
extern void d_genocide(struct dentry *);
+extern void d_genocide_safe(struct dentry *parent);
extern void d_tmpfile(struct dentry *, struct inode *);
--
2.21.0
next prev parent reply other threads:[~2019-08-01 14:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 14:02 [PATCH v2 0/4] selinux: fix race when removing selinuxfs entries Ondrej Mosnacek
2019-08-01 14:02 ` [PATCH v2 1/4] d_walk: optionally lock also parent inode Ondrej Mosnacek
2019-08-01 16:10 ` Al Viro
2019-08-01 16:12 ` Al Viro
2019-08-01 14:02 ` [PATCH v2 2/4] d_walk: add leave callback Ondrej Mosnacek
2019-08-01 14:02 ` Ondrej Mosnacek [this message]
2019-08-01 14:02 ` [PATCH v2 4/4] selinux: use d_genocide_safe() in selinuxfs Ondrej Mosnacek
2019-08-01 16:09 ` [PATCH v2 0/4] selinux: fix race when removing selinuxfs entries Al Viro
2019-08-08 7:59 ` Ondrej Mosnacek
2019-09-03 10:56 ` Ondrej Mosnacek
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