From: Matthew Bobrowski <mbobrowski@mbobrowski.org>
To: Kees Cook <keescook@chromium.org>
Cc: Jan Kara <jack@suse.cz>, Theodore Ts'o <tytso@mit.edu>,
Ritesh Harjani <riteshh@linux.ibm.com>,
"Gustavo A. R. Silva" <gustavo@embeddedor.com>,
linux-next@vger.kernel.org
Subject: Re: Coverity: ext4_iomap_alloc(): Integer handling issues
Date: Wed, 13 Nov 2019 08:28:47 +1100 [thread overview]
Message-ID: <20191112212846.GA29863@bobrowski> (raw)
In-Reply-To: <201911121256.647DA73508@keescook>
On Tue, Nov 12, 2019 at 12:56:45PM -0800, Kees Cook wrote:
> On Tue, Nov 12, 2019 at 12:00:04PM +0100, Jan Kara wrote:
> > On Tue 12-11-19 18:22:41, Matthew Bobrowski wrote:
> > > On Mon, Nov 11, 2019 at 05:35:44PM -0800, coverity-bot wrote:
> > > > This is an experimental automated report about issues detected by Coverity
> > > > from a scan of next-20191108 as part of the linux-next weekly scan project:
> > > > https://scan.coverity.com/projects/linux-next-weekly-scan
> > > >
> > > > You're getting this email because you were associated with the identified
> > > > lines of code (noted below) that were touched by recent commits:
> > > >
> > > > 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
> > > >
> > > > Coverity reported the following:
> > > >
> > > > *** CID 1487841: Integer handling issues (OVERFLOW_BEFORE_WIDEN)
> > > > /fs/ext4/inode.c: 3388 in ext4_iomap_alloc()
> > > > 3382 /*
> > > > 3383 * We use i_size instead of i_disksize here because delalloc writeback
> > > > 3384 * can complete at any point during the I/O and subsequently push the
> > > > 3385 * i_disksize out to i_size. This could be beyond where direct I/O is
> > > > 3386 * happening and thus expose allocated blocks to direct I/O reads.
> > > > 3387 */
> > > > vvv CID 1487841: Integer handling issues (OVERFLOW_BEFORE_WIDEN)
> > > > vvv Potentially overflowing expression "1 << blkbits" with type "int" (32 bits, signed) is evaluated using 32-bit arithmetic, and then used in a context that expects an expression of type "loff_t" (64 bits, signed).
> > > > 3388 else if ((map->m_lblk * (1 << blkbits)) >= i_size_read(inode))
> > > > 3389 m_flags = EXT4_GET_BLOCKS_CREATE;
> > > > 3390 else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
> > > > 3391 m_flags = EXT4_GET_BLOCKS_IO_CREATE_EXT;
> > >
> > > In the event of an overflow in this specific context, I don't think it
> > > would matter too much to be perfectly honest. If 'blkbits' were to
> > > actually ever push out the signed integer to a value that couldn't be
> > > represented by this data type, I would expect the resulting wrapping
> > > behaviour to _only_ affect how filesystem blocks are allocated. In
> > > that case, I/O workloads would behave alot differently, and at that
> > > point I would hope that our filesystem related testing infrastructure
> > > would pick this up before allowing anything to leak out into the
> > > wild...
> > >
> > > Unless my trail of thought is wrong? Happy to be corrected here and
> > > educated on this.
> >
> > Fully agreed. blkbits is never expected to be larger than 16 in this code.
> > So this is false positive.
>
> Thanks for looking into this!
No problem!
> Is it worth changing the type to u8 or something?
'blkbits' in this case is already of data type u8, so this would
effectively be a no-op. :)
/M
next prev parent reply other threads:[~2019-11-12 21:28 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-12 1:35 Coverity: ext4_iomap_alloc(): Integer handling issues coverity-bot
2019-11-12 7:22 ` Matthew Bobrowski
2019-11-12 11:00 ` Jan Kara
2019-11-12 20:56 ` Kees Cook
2019-11-12 21:28 ` Matthew Bobrowski [this message]
2019-11-12 22:17 ` Kees Cook
2019-11-13 4:38 ` Matthew Bobrowski
2019-11-13 9:37 ` Jan Kara
2019-11-13 18:38 ` Kees Cook
2019-11-14 8:58 ` Jan Kara
2019-11-14 18:43 ` Kees Cook
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