linux-ext4 - Re: [PATCH] ext4: fix undefined bit shift result in ext4_fill_flex

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Message-ID: <20121015170009.GA30787@thunk.org>
Date:	Mon, 15 Oct 2012 13:00:09 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: fix undefined bit shift result in
 ext4_fill_flex_info

On Wed, Oct 03, 2012 at 09:11:47AM +0200, Lukas Czerner wrote:
> The result of the bit shift expression in
> '1 << sbi->s_log_groups_per_flex' can be undefined in the case that
> s_log_groups_per_flex is 31 because the result of the shift is bigger
> than INT_MAX. In reality this probably should not cause much problems
> since we'll end up with INT_MIN which will then be converted into
> 'unsigned int' type, but nevertheless according to the ISO C99 the
> result is actually undefined.
> 
> Fix this by changing the left operand to 'unsigned int' type.
> 
> Note that the commit d50f2ab6f050311dbf7b8f5501b25f0bf64a439b already
> tried to fix the undefined behaviour, but this was missed.
> 
> Thanks to Laszlo Ersek for pointing this out and suggesting the fix.
> 
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> Reported-by: Laszlo Ersek <lersek@...hat.com>

Thanks, applied.

					- Ted
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