From: Al Viro <viro@zeniv.linux.org.uk>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Jordy Zomer <jordy@pwning.systems>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
"Ahmed S. Darwish" <a.darwish@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Eric Biggers <ebiggers@google.com>
Subject: Re: [PATCH] fs: make d_path-like functions all have unsigned size
Date: Tue, 27 Jul 2021 14:50:19 +0000 [thread overview]
Message-ID: <YQAdK0z5jFdw6cLz@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <20210727103625.74961-1-gregkh@linuxfoundation.org>
On Tue, Jul 27, 2021 at 12:36:25PM +0200, Greg Kroah-Hartman wrote:
> When running static analysis tools to find where signed values could
> potentially wrap the family of d_path() functions turn out to trigger a
> lot of mess. In evaluating the code, all of these usages seem safe, but
> pointer math is involved so if a negative number is ever somehow passed
> into these functions, memory can be traversed backwards in ways not
> intended.
>
> Resolve all of the abuguity by just making "size" an unsigned value,
> which takes the guesswork out of everything involved.
TBH, I'm not sure it's the right approach. Huge argument passed to d_path()
is a bad idea, no matter what. Do you really want to have the damn thing
try and fill 3Gb of buffer, all while holding rcu_read_lock() and a global
spinlock or two? Hell, s/3Gb/1Gb/ and it won't get any better...
How about we do this instead:
d_path(const struct path *path, char *buf, int buflen)
{
if (unlikely((unsigned)buflen > 0x8000)) {
buf += (unsigned)buflen - 0x8000;
buflen = 0x8000;
}
as in mainline
}
and take care of both issues?
next prev parent reply other threads:[~2021-07-27 14:52 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-27 10:36 [PATCH] fs: make d_path-like functions all have unsigned size Greg Kroah-Hartman
2021-07-27 10:49 ` Ahmed S. Darwish
2021-07-27 10:56 ` Greg Kroah-Hartman
2021-07-27 11:19 ` Matthew Wilcox
2021-07-27 11:51 ` Greg Kroah-Hartman
2021-07-27 14:50 ` Al Viro [this message]
2021-07-27 15:07 ` Matthew Wilcox
2021-07-27 15:17 ` Al Viro
2021-07-27 15:31 ` Matthew Wilcox
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