[PATCH 2.6.12.3] Deny chmod in /proc/<pid>/

[Johan Veenhuizen <veenhuizen@users.sourceforge.net>]

Hi!

This patch tries to fix the strange behaviour in /proc/<pid>/,
where it is currently possible for the owner of a process to
temporarily chmod the entries.

Since the inodes for these entries are only temporary, the
permissions will suddenly be reset when the cache is reclaimed.
This is confusing and ugly.

The fix is simple: Deny chmod for all entries in /proc/<pid>/.
I figured this would be a lot easier than maintaining persistent
modes.  The patch does also trigger an EPERM when someone tries
to chown/chgrp an entry (which is currently silently ignored).

Please send comments, corrections and suggestions.

	Johan Veenhuizen


--- linux-2.6.12.3/fs/proc/base.c	2005-07-15 23:18:57.000000000 +0200
+++ linux-2.6.12.3-jpv/fs/proc/base.c	2005-08-02 20:08:36.000000000 +0200
@@ -496,6 +496,17 @@
 	return proc_check_root(inode);
 }
 
+static int proc_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	unsigned int ia_valid = attr->ia_valid;
+
+	if ((ia_valid & ATTR_MODE) || (ia_valid & ATTR_UID)
+	                           || (ia_valid & ATTR_GID))
+		return -EPERM;
+	else
+		return inode_setattr(dentry->d_inode, attr);
+}
+
 extern struct seq_operations proc_pid_maps_op;
 static int maps_open(struct inode *inode, struct file *file)
 {
@@ -766,8 +777,13 @@
 	.write		= oom_adjust_write,
 };
 
+static struct inode_operations proc_default_inode_operations = {
+	.setattr	= proc_setattr,
+};
+
 static struct inode_operations proc_mem_inode_operations = {
 	.permission	= proc_permission,
+	.setattr	= proc_setattr,
 };
 
 #ifdef CONFIG_AUDITSYSCALL
@@ -965,7 +981,8 @@
 
 static struct inode_operations proc_pid_link_inode_operations = {
 	.readlink	= proc_pid_readlink,
-	.follow_link	= proc_pid_follow_link
+	.follow_link	= proc_pid_follow_link,
+	.setattr	= proc_setattr,
 };
 
 #define NUMBUF 10
@@ -1133,6 +1150,7 @@
 	ei->task = NULL;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	inode->i_ino = fake_ino(task->pid, ino);
+	inode->i_op = &proc_default_inode_operations;
 
 	if (!pid_alive(task))
 		goto out_unlock;
@@ -1349,11 +1367,13 @@
 static struct inode_operations proc_fd_inode_operations = {
 	.lookup		= proc_lookupfd,
 	.permission	= proc_permission,
+	.setattr	= proc_setattr,
 };
 
 static struct inode_operations proc_task_inode_operations = {
 	.lookup		= proc_task_lookup,
 	.permission	= proc_permission,
+	.setattr	= proc_setattr,
 };
 
 #ifdef CONFIG_SECURITY
@@ -1627,10 +1647,12 @@
 
 static struct inode_operations proc_tgid_base_inode_operations = {
 	.lookup		= proc_tgid_base_lookup,
+	.setattr	= proc_setattr,
 };
 
 static struct inode_operations proc_tid_base_inode_operations = {
 	.lookup		= proc_tid_base_lookup,
+	.setattr	= proc_setattr,
 };
 
 #ifdef CONFIG_SECURITY
@@ -1672,10 +1694,12 @@
 
 static struct inode_operations proc_tgid_attr_inode_operations = {
 	.lookup		= proc_tgid_attr_lookup,
+	.setattr	= proc_setattr,
 };
 
 static struct inode_operations proc_tid_attr_inode_operations = {
 	.lookup		= proc_tid_attr_lookup,
+	.setattr	= proc_setattr,
 };
 #endif
 
@@ -1700,6 +1724,7 @@
 static struct inode_operations proc_self_inode_operations = {
 	.readlink	= proc_self_readlink,
 	.follow_link	= proc_self_follow_link,
+	.setattr	= proc_setattr,
 };
 
 /**
-
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