linux-kernel - Re: [PATCH 1/2] fs: Fix sign extension problem in sys

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Wed, 25 Mar 2009 12:33:44 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	dann frazier <dannf@...nf.org>, linux-mips@...ux-mips.org
Subject: Re: [PATCH 1/2] fs: Fix sign extension problem in sys_llseek

On Wed, 25 Mar 2009 01:13:03 +0100
Ralf Baechle <ralf@...ux-mips.org> wrote:

> In fs/read_write.c:
> 
> SYSCALL_DEFINE5(llseek, unsigned int, fd, unsigned long, offset_high,
>                 unsigned long, offset_low, loff_t __user *, result,
>                 unsigned int, origin)
> ...
>    	offset = vfs_llseek(file, ((loff_t) offset_high << 32) | offset_low,
>                         origin);
> 
> On a 64-bit system that define CONFIG_HAVE_SYSCALL_WRAPPERS SYSCALL_DEFINEx
> will truncate long arguments to 32-bit and on some architectures such as
> MIPS sign-extended to 64-bit again.  On such architectures passing a
> value with bit 31 in offset_low set will result in a huge 64-bit offset
> being passed to vfs_llseek() and it failiing with EINVAL.

How is that possible? If you have CONFIG_HAVE_SYSCALL_WRAPPERS defined
then the wrapper will (in this case) cast offset_low from long to
unsigned long. It won't truncate or sign extend anything here.
The whole operation should be a NOP.

This is what you get after macro expansion (BUILD_BUG_ON removed):

long sys_llseek(unsigned int fd, unsigned long offset_high, unsigned long offset_low, loff_t * result, unsigned int origin);

static inline __attribute__((always_inline))
long SYSC_llseek(unsigned int fd, unsigned long offset_high, unsigned long offset_low, loff_t * result, unsigned int origin);

long SyS_llseek(long fd, long offset_high, long offset_low, long result, long origin)
{
	return (long) SYSC_llseek((unsigned int) fd, (unsigned long) offset_high, (unsigned long) offset_low, (loff_t *) result, (unsigned int) origin);
}

asm ("\t.globl " "sys_llseek" "\n\t.set " "sys_llseek" ", " "SyS_llseek");

static inline __attribute__((always_inline))
long SYSC_llseek(unsigned int fd, unsigned long offset_high, unsigned long offset_low, loff_t * result, unsigned int origin)
{
	[...]
}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/