linux-kernel - [PATCH 4.19 6/7] proc: Use d_invalidate in proc_prune_siblings

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Message-Id: <20210107075314.62683-7-wenyang@linux.alibaba.com>
Date:   Thu,  7 Jan 2021 15:53:13 +0800
From:   Wen Yang <wenyang@...ux.alibaba.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sasha Levin <sashal@...nel.org>
Cc:     Xunlei Pang <xlpang@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        stable@...r.kernel.org, Wen Yang <wenyang@...ux.alibaba.com>
Subject: [PATCH 4.19 6/7] proc: Use d_invalidate in proc_prune_siblings_dcache

From: "Eric W. Biederman" <ebiederm@...ssion.com>

[ Upstream commit f90f3cafe8d56d593fc509a4185da1d5800efea4 ]

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.

For completeness the directory and the non-directory cases are
separated because in theory (although not in currently in practice for
proc) directories can only ever have a single dentry while
non-directories can have hardlinks and thus multiple dentries.
As part of this separation use d_find_any_alias for directories
to spare d_find_alias the extra work of doing that.

Plus the differences between d_find_any_alias and d_find_alias makes
it clear why the directory and non-directory code and not share code.

To make it clear these routines now invalidate dentries rename
proc_prune_siblings_dache to proc_invalidate_siblings_dcache, and rename
proc_sys_prune_dcache proc_sys_invalidate_dcache.

V2: Split the directory and non-directory cases.  To make this
    code robust to future changes in proc.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Cc: <stable@...r.kernel.org> # 4.19.x
Signed-off-by: Wen Yang <wenyang@...ux.alibaba.com>
---
 fs/proc/inode.c       | 16 ++++++++++++++--
 fs/proc/internal.h    |  2 +-
 fs/proc/proc_sysctl.c |  8 ++++----
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 45b4344..fad579e 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -118,7 +118,7 @@ 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;
@@ -147,7 +147,19 @@ void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 			continue;
 		}
 
-		d_prune_aliases(inode);
+		if (S_ISDIR(inode->i_mode)) {
+			struct dentry *dir = d_find_any_alias(inode);
+			if (dir) {
+				d_invalidate(dir);
+				dput(dir);
+			}
+		} else {
+			struct dentry *dentry;
+			while ((dentry = d_find_alias(inode))) {
+				d_invalidate(dentry);
+				dput(dentry);
+			}
+		}
 		iput(inode);
 		deactivate_super(sb);
 
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 6cae472..1db693b 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -210,7 +210,7 @@ struct pde_opener {
 extern const struct inode_operations proc_pid_link_inode_operations;
 
 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 int proc_fill_super(struct super_block *, void *data, int flags);
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 57b16bf..f8f1f8a 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -262,9 +262,9 @@ 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 */
@@ -286,10 +286,10 @@ 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.
-- 
1.8.3.1