[ 3.5.y.z extended stable ] Patch "vfs, proc: guarantee unique inodes in /proc" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Mon Mar 25 18:03:19 UTC 2013


This is a note to let you know that I have just added a patch titled

    vfs,proc: guarantee unique inodes in /proc

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 73f80275e96612c055b4b18e74ece4c0964c4988 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds at linux-foundation.org>
Date: Fri, 22 Mar 2013 11:44:04 -0700
Subject: [PATCH] vfs,proc: guarantee unique inodes in /proc

commit 51f0885e5415b4cc6535e9cdcc5145bfbc134353 upstream.

Dave Jones found another /proc issue with his Trinity tool: thanks to
the namespace model, we can have multiple /proc dentries that point to
the same inode, aliasing directories in /proc/<pid>/net/ for example.

This ends up being a total disaster, because it acts like hardlinked
directories, and causes locking problems.  We rely on the topological
sort of the inodes pointed to by dentries, and if we have aliased
directories, that odering becomes unreliable.

In short: don't do this.  Multiple dentries with the same (directory)
inode is just a bad idea, and the namespace code should never have
exposed things this way.  But we're kind of stuck with it.

This solves things by just always allocating a new inode during /proc
dentry lookup, instead of using "iget_locked()" to look up existing
inodes by superblock and number.  That actually simplies the code a bit,
at the cost of potentially doing more inode [de]allocations.

That said, the inode lookup wasn't free either (and did a lot of locking
of inodes), so it is probably not that noticeable.  We could easily keep
the old lookup model for non-directory entries, but rather than try to
be excessively clever this just implements the minimal and simplest
workaround for the problem.

Reported-and-tested-by: Dave Jones <davej at redhat.com>
Analyzed-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
[ luis: backported to 3.5; adjust context ]
Luis Henriques <luis.henriques at canonical.com>
---
 fs/proc/inode.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 7ac817b..b02ddd0 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -443,12 +443,10 @@ static const struct file_operations proc_reg_file_ops_no_compat = {

 struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
 {
-	struct inode * inode;
+	struct inode *inode = new_inode_pseudo(sb);

-	inode = iget_locked(sb, de->low_ino);
-	if (!inode)
-		return NULL;
-	if (inode->i_state & I_NEW) {
+	if (inode) {
+		inode->i_ino = de->low_ino;
 		inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 		PROC_I(inode)->fd = 0;
 		PROC_I(inode)->pde = de;
@@ -477,7 +475,6 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
 				inode->i_fop = de->proc_fops;
 			}
 		}
-		unlock_new_inode(inode);
 	} else
 	       pde_put(de);
 	return inode;
--
1.8.1.2





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