linux-kernel - Re: [PATCH] proc: avoid extra pde_put() in proc_fill

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20130123161715.GX4939@ZenIV.linux.org.uk>
Date:	Wed, 23 Jan 2013 16:17:15 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Maxim Patlasov <mpatlasov@...allels.com>
Cc:	ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
	dhowells@...hat.com, akpm@...ux-foundation.org,
	fengguang.wu@...el.com, devel@...nvz.org
Subject: Re: [PATCH] proc: avoid extra pde_put() in proc_fill_super()

On Tue, Jan 22, 2013 at 09:03:26PM +0400, Maxim Patlasov wrote:
> If proc_get_inode() succeeded, but d_make_root() failed, pde_put() for
> proc_root will be called twice: the first time due to iput() called from
> d_make_root() and the second time directly in the end of proc_fill_super().

I don't like that solution, TBH.  How about making proc_get_inode() call
pde_put() on failure instead?  Note that it already does so if inode had
been found in icache, so this will just make the refcounting consistent.
Completely untested patch follows:

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 76ddae8..8b487e5 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -413,31 +413,24 @@ struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *dir,
 		struct dentry *dentry)
 {
 	struct inode *inode = NULL;
-	int error = -ENOENT;
 
 	spin_lock(&proc_subdir_lock);
 	for (de = de->subdir; de ; de = de->next) {
 		if (de->namelen != dentry->d_name.len)
 			continue;
-		if (!memcmp(dentry->d_name.name, de->name, de->namelen)) {
-			pde_get(de);
-			spin_unlock(&proc_subdir_lock);
-			error = -ENOMEM;
-			inode = proc_get_inode(dir->i_sb, de);
-			goto out_unlock;
-		}
-	}
-	spin_unlock(&proc_subdir_lock);
-out_unlock:
-
-	if (inode) {
+		if (memcmp(dentry->d_name.name, de->name, de->namelen))
+			continue;
+		pde_get(de);
+		spin_unlock(&proc_subdir_lock);
+		inode = proc_get_inode(dir->i_sb, de);
+		if (!inode)
+			return ERR_PTR(-ENOMEM);
 		d_set_d_op(dentry, &proc_dentry_operations);
 		d_add(dentry, inode);
 		return NULL;
 	}
-	if (de)
-		pde_put(de);
-	return ERR_PTR(error);
+	spin_unlock(&proc_subdir_lock);
+	return ERR_PTR(-ENOENT);
 }
 
 struct dentry *proc_lookup(struct inode *dir, struct dentry *dentry,
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 439ae688..e2bbe20 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -448,9 +448,7 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
 	struct inode * inode;
 
 	inode = iget_locked(sb, de->low_ino);
-	if (!inode)
-		return NULL;
-	if (inode->i_state & I_NEW) {
+	if (inode && inode->i_state & I_NEW) {
 		inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 		PROC_I(inode)->pde = de;
 
@@ -499,6 +497,5 @@ int proc_fill_super(struct super_block *s)
 		return 0;
 
 	printk("proc_read_super: get root inode failed\n");
-	pde_put(&proc_root);
 	return -ENOMEM;
 }
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/