linux-kernel - [PATCH]: Revert 2.6.36 chroot ttyname regression

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Message-ID: <m1oc90n6qp.fsf@fess.ebiederm.org>
Date:	Sat, 04 Dec 2010 21:11:58 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	stable@...nel.org
Subject: [PATCH]: Revert 2.6.36 chroot ttyname regression

As of 2.6.36 ttyname does not work in a chroot.  It has already
been reported that screen breaks, and for me this breaks an automated
distribution testsuite, that I need to preserve the ability to run
the existing binaries on for several more years.  glibc 2.11.3 which
has a fix for this is not an option.

The root cause of this breakage is:
commit 8df9d1a4142311c084ffeeacb67cd34d190eff74
Author: Miklos Szeredi <mszeredi@...e.cz>
Date:   Tue Aug 10 11:41:41 2010 +0200

    vfs: show unreachable paths in getcwd and proc

    Prepend "(unreachable)" to path strings if the path is not reachable
    from the current root.

    Two places updated are
     - the return string from getcwd()
     - and symlinks under /proc/$PID.

    Other uses of d_path() are left unchanged (we know that some old
    software crashes if /proc/mounts is changed).

    Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
    Signed-off-by: Al Viro <viro@...iv.linux.org.uk>

So remove the nice sounding, but ultimately ill advised change to how
/proc/fd symlinks work.

Index: linux-2.6.37-rc4.x86_64/fs/proc/base.c
===================================================================
--- linux-2.6.37-rc4.x86_64.orig/fs/proc/base.c
+++ linux-2.6.37-rc4.x86_64/fs/proc/base.c
@@ -1574,7 +1574,7 @@ static int do_proc_readlink(struct path 
 	if (!tmp)
 		return -ENOMEM;

-	pathname = d_path_with_unreachable(path, tmp, PAGE_SIZE);
+	pathname = d_path(path, tmp, PAGE_SIZE);
 	len = PTR_ERR(pathname);
 	if (IS_ERR(pathname))
 		goto out;
--
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