linux-kernel - [PATCH 09/17] proc: merge proc_ns_readlink() into proc_ns_get

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Date:   Mon, 12 Sep 2016 21:29:11 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: [PATCH 09/17] proc: merge proc_ns_readlink() into proc_ns_get_link()

This will allow us to move the generic readlink logic into the VFS and get
rid of the readlink method.

Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
---
 fs/proc/namespaces.c | 56 +++++++++++++++++++++++++++-------------------------
 1 file changed, 29 insertions(+), 27 deletions(-)

diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 51b8b0a8ad91..9c9a1683791a 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -33,6 +33,8 @@ static const struct proc_ns_operations *ns_entries[] = {
 #endif
 };
 
+#define PROC_NS_LINK_MAX 50
+
 static const char *proc_ns_get_link(struct dentry *dentry,
 				    struct inode *inode,
 				    struct delayed_call *done)
@@ -40,47 +42,47 @@ static const char *proc_ns_get_link(struct dentry *dentry,
 	const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops;
 	struct task_struct *task;
 	struct path ns_path;
-	void *error = ERR_PTR(-EACCES);
+	char *res = ERR_PTR(-EACCES);
 
 	if (!dentry)
 		return ERR_PTR(-ECHILD);
 
 	task = get_proc_task(inode);
 	if (!task)
-		return error;
-
-	if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) {
-		error = ns_get_path(&ns_path, task, ns_ops);
-		if (!error)
-			nd_jump_link(&ns_path);
-	}
-	put_task_struct(task);
-	return error;
-}
-
-static int proc_ns_readlink(struct dentry *dentry, char __user *buffer, int buflen)
-{
-	struct inode *inode = d_inode(dentry);
-	const struct proc_ns_operations *ns_ops = PROC_I(inode)->ns_ops;
-	struct task_struct *task;
-	char name[50];
-	int res = -EACCES;
+		goto out;
 
-	task = get_proc_task(inode);
-	if (!task)
-		return res;
+	if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS))
+		goto out_put;
 
-	if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) {
-		res = ns_get_name(name, sizeof(name), task, ns_ops);
-		if (res >= 0)
-			res = readlink_copy(buffer, buflen, name);
+	if (is_following_link()) {
+		res = ns_get_path(&ns_path, task, ns_ops);
+		if (!res)
+			nd_jump_link(&ns_path);
+	} else {
+		char *name = kmalloc(PROC_NS_LINK_MAX, GFP_KERNEL);
+		int err;
+
+		res = ERR_PTR(-ENOMEM);
+		if (!name)
+			goto out_put;
+
+		err = ns_get_name(name, PROC_NS_LINK_MAX, task, ns_ops);
+		if (err < 0) {
+			kfree(name);
+			res = ERR_PTR(err);
+			goto out_put;
+		}
+		set_delayed_call(done, kfree_link, name);
+		res = name;
 	}
+out_put:
 	put_task_struct(task);
+out:
 	return res;
 }
 
 static const struct inode_operations proc_ns_link_inode_operations = {
-	.readlink	= proc_ns_readlink,
+	.readlink	= generic_readlink,
 	.get_link	= proc_ns_get_link,
 	.setattr	= proc_setattr,
 };
-- 
2.5.5