linux-kernel - [PATCH 4/7] proc: Use d_invalidate in proc_prune_siblings

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Date:   Thu, 20 Feb 2020 14:49:53 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Security Module <linux-security-module@...r.kernel.org>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Solar Designer <solar@...nwall.com>
Subject: [PATCH 4/7] proc: Use d_invalidate in proc_prune_siblings_dcache


The function d_prune_aliases has the problem that it will only prune
aliases thare are completely unused.  It will not remove aliases for
the dcache or even think of removing mounts from the dcache.  For that
behavior d_invalidate is needed.

To use d_invalidate replace d_prune_aliases with d_find_alias
followed by d_invalidate and dput.  This is safe and complete
because no inode in proc has any hardlinks or aliases.

To make this behavior change clear rename
proc_prune_siblings_dache proc_invalidate_siblings_dcache,
and rename proc_sys_prune_dcache proc_sys_invalidate_dcache.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/proc/inode.c       | 9 +++++++--
 fs/proc/internal.h    | 2 +-
 fs/proc/proc_sysctl.c | 8 ++++----
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 38a7baa41aba..c4528c419876 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -103,12 +103,13 @@ void __init proc_init_kmemcache(void)
 	BUILD_BUG_ON(sizeof(struct proc_dir_entry) >= SIZEOF_PDE);
 }
 
-void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
+void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 {
 	struct inode *inode;
 	struct proc_inode *ei;
 	struct hlist_node *node;
 	struct super_block *sb;
+	struct dentry *dentry;
 
 	for (;;) {
 		rcu_read_lock();
@@ -135,7 +136,11 @@ void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 			continue;
 		}
 
-		d_prune_aliases(inode);
+		dentry = d_find_alias(inode);
+		if (dentry) {
+			d_invalidate(dentry);
+			dput(dentry);
+		}
 		iput(inode);
 		deactivate_super(sb);
 	}
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index ba9a991824a5..fd470172675f 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -210,7 +210,7 @@ extern const struct inode_operations proc_pid_link_inode_operations;
 extern const struct super_operations proc_sops;
 
 void proc_init_kmemcache(void);
-void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock);
+void proc_invalidate_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock);
 void set_proc_pid_nlink(void);
 extern struct inode *proc_get_inode(struct super_block *, struct proc_dir_entry *);
 extern void proc_entry_rundown(struct proc_dir_entry *);
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 5da9d7f7ae34..b6f5d459b087 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -267,9 +267,9 @@ static void unuse_table(struct ctl_table_header *p)
 			complete(p->unregistering);
 }
 
-static void proc_sys_prune_dcache(struct ctl_table_header *head)
+static void proc_sys_invalidate_dcache(struct ctl_table_header *head)
 {
-	proc_prune_siblings_dcache(&head->inodes, &sysctl_lock);
+	proc_invalidate_siblings_dcache(&head->inodes, &sysctl_lock);
 }
 
 /* called under sysctl_lock, will reacquire if has to wait */
@@ -291,10 +291,10 @@ static void start_unregistering(struct ctl_table_header *p)
 		spin_unlock(&sysctl_lock);
 	}
 	/*
-	 * Prune dentries for unregistered sysctls: namespaced sysctls
+	 * Invalidate dentries for unregistered sysctls: namespaced sysctls
 	 * can have duplicate names and contaminate dcache very badly.
 	 */
-	proc_sys_prune_dcache(p);
+	proc_sys_invalidate_dcache(p);
 	/*
 	 * do not remove from the list until nobody holds it; walking the
 	 * list in do_sysctl() relies on that.
-- 
2.20.1