On Thu, 30 Jan 2014 05:28:27 -0800 Greg Kroah-Hartman <gre...@linuxfoundation.org> wrote:
> On Thu, Jan 30, 2014 at 09:48:02AM +0100, Petr Tesarik wrote: > > The loff_t type may be wider than phys_addr_t (e.g. on 32-bit systems). > > Consequently, the file offset may be truncated in the assignment. > > Currently, /dev/mem wraps around, which may cause applications to read > > or write incorrect regions of memory by accident. > > Does that really happen? If so, that's a userspace bug, right? In my case, it was a userspace bug, indeed. But debugging would have been much easier if I saw read() fail with an EOF condition, rather than pretend that it actually read some bytes (from above 4G) on a 32-bit box. > > Let's follow POSIX file semantics here and return 0 when reading from > > and -EFBIG when writing to an offset that cannot be represented by a > > phys_addr_t. > > > > Note that the conditional is optimized out by the compiler if loff_t > > has the same size as phys_addr_t. > > > > Signed-off-by: Petr Tesarik <ptesa...@suse.cz> > > --- > > drivers/char/mem.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > What is going to break if we apply this patch? :) Nothing, unless it was broken already. I mean, if anyone is trying to play dirty tricks with 32-bit file offset overflow, I'd call such code sick and broken. And on 64-bit platforms, the patch does not even change the generated code. Petr T -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
