linux-kernel - Re: BUG_ON(nd->inode->i_op->follow

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Date:	Thu, 7 Mar 2013 18:03:02 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: BUG_ON(nd->inode->i_op->follow_link);

On Thu, Mar 07, 2013 at 02:50:55PM -0800, Linus Torvalds wrote:

 > Yes, I can reproduce this, and I know what's going on. I don't have a
 > patch, though, and I think it's in Al's court on what we should do.
 > Al?
 > 
 > Anyway, so the "old=fd" thing implies that it's one of the symlinks in
 > /proc/xyz/fd/, so that's something. It could have been the
 > cwd/exe/mmap ones. But that was kind of the expectation to begin with.
 > 
 > The "new=1:9" is the path that the file descriptor contained, and
 > since you're playing games with /proc, /sys and /dev, *and* since you
 > hit the "it shouldn't be a symlink" test, I'm *guessing* that it might
 > be something like
 > 
 >     /sys/dev/char/1:9

Strange, I told it to *only* use /proc on that run, so it shouldn't have sucked
in anything from /dev unless something in /proc symlinks there and nftw()
ended up chasing it.

 > which is a symlink to ../../devices/virtual/mem/urandom/.
 > 
 > And here is how you reproduce this:

But this at least is one step towards restoring my belief that I'm not
going crazy here.

 > Al, I think the BUG_ON() is simply bogus. Should we just remove it? Or
 > is there some conceptual reason why we can't handle a symlink there?

For the time being, I'll remove that just so I can stop seeing it,
as it seems there's plenty of others to be chasing and you've got
a handle on this one.

	Dave

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