linux-kernel - [PATCH 1/1] fs-sysfs bugfix of sysfs_hash_and_remove dereferencing before checking for NULL

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Date:	Fri, 22 Jun 2007 10:13:24 -0700 (PDT)
From:	Doug Thompson <norsk5@...oo.com>
To:	Greg K-H <greg@...ah.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 1/1] fs-sysfs bugfix of sysfs_hash_and_remove dereferencing before checking for NULL

From:	Douglas Thompson <dougthompson@...ssion.com>

In tracking down one of my bugs in using sysfs, I found the kernel doing a NULL de-reference
in function fs/sysfs/inode.c:sysfs_hash_and_remove(), when I (incorrectly) passed
in a dentry value of NULL.

The check for NULL should occur BEFORE the dereference of 'dir'. 
This patch modifies the sequence and does the check FIRST


Signed-off-by:	Douglas Thompson <dougthompson@...ssion.com>
---

Index: linux-2.6.22-rc4-mm2/fs/sysfs/inode.c
===================================================================
--- linux-2.6.22-rc4-mm2.orig/fs/sysfs/inode.c
+++ linux-2.6.22-rc4-mm2/fs/sysfs/inode.c
@@ -285,7 +285,7 @@ void sysfs_drop_dentry(struct sysfs_dire
 int sysfs_hash_and_remove(struct dentry * dir, const char * name)
 {
 	struct sysfs_dirent **pos, *sd;
-	struct sysfs_dirent *parent_sd = dir->d_fsdata;
+	struct sysfs_dirent *parent_sd;
 	int found = 0;
 
 	if (!dir)
@@ -295,6 +295,8 @@ int sysfs_hash_and_remove(struct dentry 
 		/* no inode means this hasn't been made visible yet */
 		return -ENOENT;
 
+	parent_sd = dir->d_fsdata;
+
 	mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_PARENT);
 	for (pos = &parent_sd->s_children; *pos; pos = &(*pos)->s_sibling) {
 		sd = *pos;
-
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