Don't allow chmod() on the /proc/<pid>/ files

This just turns off chmod() on the /proc/<pid>/ files, since there is no
good reason to allow it, and had we disallowed it originally, the nasty
/proc race exploit wouldn't have been possible.

The other patches already fixed the problem chmod() could cause, so this
is really just some final mop-up..

This particular version is based off a patch by Eugene and Marcel which
had much better naming than my original equivalent one.

Signed-off-by: Eugene Teo <eteo@redhat.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 30 insertions, 1 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 474eae345068..fe8d55fb17cc 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -551,6 +551,27 @@ static int proc_fd_access_allowed(struct inode *inode)
         return allowed;
 }
 
+static int proc_setattr(struct dentry *dentry, struct iattr *attr)
+{
+        int error;
+        struct inode *inode = dentry->d_inode;
+
+        if (attr->ia_valid & ATTR_MODE)
+                return -EPERM;
+
+        error = inode_change_ok(inode, attr);
+        if (!error) {
+                error = security_inode_setattr(dentry, attr);
+                if (!error)
+                        error = inode_setattr(inode, attr);
+        }
+        return error;
+}
+
+static struct inode_operations proc_def_inode_operations = {
+        .setattr        = proc_setattr,
+};
+
 extern struct seq_operations mounts_op;
 struct proc_mounts {
         struct seq_file m;
@@ -1111,7 +1132,8 @@ out:
 
 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,
 };
 
 static int proc_readfd(struct file * filp, void * dirent, filldir_t filldir)
@@ -1285,6 +1307,7 @@ static struct inode *proc_pid_make_inode(struct super_block * sb, struct task_st
         ei = PROC_I(inode);
         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
         inode->i_ino = fake_ino(task->pid, ino);
+        inode->i_op = &proc_def_inode_operations;
 
         /*
          * grab the reference to task.
@@ -1529,11 +1552,13 @@ static struct file_operations proc_task_operations = {
  */
 static struct inode_operations proc_fd_inode_operations = {
         .lookup         = proc_lookupfd,
+        .setattr        = proc_setattr,
 };
 
 static struct inode_operations proc_task_inode_operations = {
         .lookup         = proc_task_lookup,
         .getattr        = proc_task_getattr,
+        .setattr        = proc_setattr,
 };
 
 #ifdef CONFIG_SECURITY
@@ -1847,11 +1872,13 @@ static struct file_operations proc_tid_base_operations = {
 static struct inode_operations proc_tgid_base_inode_operations = {
         .lookup         = proc_tgid_base_lookup,
         .getattr        = pid_getattr,
+        .setattr        = proc_setattr,
 };
 
 static struct inode_operations proc_tid_base_inode_operations = {
         .lookup         = proc_tid_base_lookup,
         .getattr        = pid_getattr,
+        .setattr        = proc_setattr,
 };
 
 #ifdef CONFIG_SECURITY
@@ -1894,11 +1921,13 @@ static struct dentry *proc_tid_attr_lookup(struct inode *dir,
 static struct inode_operations proc_tgid_attr_inode_operations = {
         .lookup         = proc_tgid_attr_lookup,
         .getattr        = pid_getattr,
+        .setattr        = proc_setattr,
 };
 
 static struct inode_operations proc_tid_attr_inode_operations = {
         .lookup         = proc_tid_attr_lookup,
         .getattr        = pid_getattr,
+        .setattr        = proc_setattr,
 };
 #endif