From: Matthew Wilcox <willy@infradead.org>
To: Alejandro Colomar <alx@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, Jan Engelhardt <jengelh@inai.de>,
linux-man@vger.kernel.org
Subject: Re: Undefined Behavior in rw_verify_area() (was: sendfile(2) erroneously yields EINVAL on too large counts)
Date: Mon, 4 Mar 2024 15:22:24 +0000 [thread overview]
Message-ID: <ZeXnMO0DcZH63B_d@casper.infradead.org> (raw)
In-Reply-To: <ZeXkLYExJHj98oaS@debian>
On Mon, Mar 04, 2024 at 04:09:26PM +0100, Alejandro Colomar wrote:
> Depending on the width of those types, the sum may be performed as
> 'loff_t' if `sizeof(loff_t) > sizeof(size_t)`, or as 'size_t' if
> `sizeof(loff_t) <= sizeof(size_t)`. Since 'loff_t' is a 64-bit type,
> but 'size_t' can be either 32-bit or 64-bit, the former is possible.
>
> In those platforms in which loff_t is wider, the addends are promoted to
> 'loff_t' before the sum. And a sum of positive signed values can never
> be negative. If the sum overflows (and the program above triggers
> such an overflow), the behavior is undefined.
Linux is compiled with -fwrapv so it is defined.
next prev parent reply other threads:[~2024-03-04 15:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-15 13:49 sendfile(2) erroneously yields EINVAL on too large counts Jan Engelhardt
2024-03-04 13:52 ` Alejandro Colomar
2024-03-04 15:09 ` Undefined Behavior in rw_verify_area() (was: sendfile(2) erroneously yields EINVAL on too large counts) Alejandro Colomar
2024-03-04 15:22 ` Matthew Wilcox [this message]
2024-03-04 15:31 ` Alejandro Colomar
2024-03-10 18:35 ` sendfile(2) erroneously yields EINVAL on too large counts Jan Engelhardt
2024-03-10 18:53 ` Alejandro Colomar
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