linux-kernel - Re: [PATCH 053/190] Revert "ecryptfs: replace BUG

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Message-ID: <20210421161329.GD4991@sequoia>
Date:   Wed, 21 Apr 2021 11:13:29 -0500
From:   Tyler Hicks <code@...icks.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Aditya Pakki <pakki001@....edu>
Subject: Re: [PATCH 053/190] Revert "ecryptfs: replace BUG_ON with error
 handling code"

On 2021-04-21 16:04:02, Al Viro wrote:
> On Wed, Apr 21, 2021 at 02:58:48PM +0200, Greg Kroah-Hartman wrote:
> > This reverts commit 2c2a7552dd6465e8fde6bc9cccf8d66ed1c1eb72.
> > 
> > Commits from @umn.edu addresses have been found to be submitted in "bad
> > faith" to try to test the kernel community's ability to review "known
> > malicious" changes.  The result of these submissions can be found in a
> > paper published at the 42nd IEEE Symposium on Security and Privacy
> > entitled, "Open Source Insecurity: Stealthily Introducing
> > Vulnerabilities via Hypocrite Commits" written by Qiushi Wu (University
> > of Minnesota) and Kangjie Lu (University of Minnesota).
> > 
> > Because of this, all submissions from this group must be reverted from
> > the kernel tree and will need to be re-reviewed again to determine if
> > they actually are a valid fix.  Until that work is complete, remove this
> > change to ensure that no problems are being introduced into the
> > codebase.
> 
> FWIW, commit message on the original (
> ecryptfs: replace BUG_ON with error handling code
> 
> In crypt_scatterlist, if the crypt_stat argument is not set up
> correctly, the kernel crashes. Instead, by returning an error code
> upstream, the error is handled safely.
> 
> The issue is detected via a static analysis tool written by us.
> 
> Fixes: 237fead619984 (ecryptfs: fs/Makefile and fs/Kconfig)
> Signed-off-by: Aditya Pakki <pakki001@....edu>
> Signed-off-by: Tyler Hicks <code@...icks.com>
> )
> really stinks.  First, the analysis: condition being tested is
> (!crypt_stat || !crypt_stat->tfm
>                || !(crypt_stat->flags & ECRYPTFS_STRUCT_INITIALIZED))
> and their patch replaces BUG_ON() with return of -EINVAL.  So the
> only thing their tool had detected the presence of BUG_ON().
> Was it grep, by any chance?  
> 
> IOW, the commit message is "we'd found BUG_ON(); let's replace it
> with returning some error value and hope everything works.  Whaddya
> mean, how do we know?  Our tool [git grep BUG_ON, that is] says
> it's there and look, it *is* there, so if it's ever reached there'll
> be trouble.  What, assertion that returning an error will be handled
> safely?   'Cuz we saiz so, that's why"
> 
> 
> It *is* functionally harmless, AFAICS, but only because the condition
> is really impossible.  However,
> 	* it refers to vague (s)tool they'd produced, nevermind that
> all they really do is "find BUG_ON(), replace with returning an error".
> 	* unlike BUG_ON(), the replacement does *NOT* document the
> fact that condition should be impossible.
> IMO either should be sufficient for rejecting the patch.

I agree that it was not a malicious change. There are other places
within the same function that return -EINVAL and the expectation is that
errors from this function should be handled safely.

That said, I can find no real-world reports of this BUG_ON() ever being
a problem and I don't think that there's any actual need for this
change. So, I'm alright with it being reverted considering the
circumstances.

 Acked-by: Tyler Hicks <code@...icks.com>

Tyler