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

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Message-ID: <YIBM8hiBLFO+JJr/@zeniv-ca.linux.org.uk>
Date:   Wed, 21 Apr 2021 16:04:02 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, Aditya Pakki <pakki001@....edu>,
        Tyler Hicks <code@...icks.com>
Subject: Re: [PATCH 053/190] Revert "ecryptfs: replace BUG_ON with error
 handling code"

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.