Re: [PATCH 3.16 296/346] fix minor infoleak in get_user_ex()

[Ben Hutchings]

On Sun, 2016-11-13 at 18:14 -0800, Linus Torvalds wrote:
> No, this is no good.
> 
> I had a slightly different version of this that is OK for older
> kernels.

And I thought I'd dropped this after you mentioned the problem at
Kernel Summit.  Thanks for checking.

Sasha, this still needs to be reverted in 3.18 and 4.1 stable branches.

Ben.

> ÂÂÂÂÂLinus
> 
> On Nov 13, 2016 6:04 PM, "Ben Hutchings" <ben@xxxxxxxxxxxxxxx> wrote:
> 
> > 3.16.39-rc1 review patch.ÂÂIf anyone has any objections, please let me
> > know.
> > 
> > ------------------
> > 
> > From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > 
> > commit 1c109fabbd51863475cd12ac206bdd249aee35af upstream.
> > 
> > get_user_ex(x, ptr) should zero x on failure.ÂÂIt's not a lot of a leak
> > (at most we are leaking uninitialized 64bit value off the kernel stack,
> > and in a fairly constrained situation, at that), but the fix is trivial,
> > so...
> > 
> > > Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > [ This sat in different branch from the uaccess fixes since mid-August ]
> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
> > ---
> > Âarch/x86/include/asm/uaccess.h | 6 +++++-
> > Â1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > --- a/arch/x86/include/asm/uaccess.h
> > +++ b/arch/x86/include/asm/uaccess.h
> > @@ -391,7 +391,11 @@ do {
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > Â#define __get_user_asm_ex(x, addr, itype, rtype, ltype)
> > ÂÂÂÂÂÂ\
> > ÂÂÂÂÂÂÂÂasm volatile("1:ÂÂÂÂÂÂÂÂmov"itype" %1,%"rtype"0\n"ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ"2:\n"ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ_ASM_EXTABLE_EX(1b, 2b)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ".section .fixup,\"ax\"\n"ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ"3:xor"itype" %"rtype"0,%"rtype"0\n"ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ"ÂÂjmp 2b\n"ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ".previous\n"ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ_ASM_EXTABLE_EX(1b, 3b)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ: ltype(x) : "m" (__m(addr)))
> > 
> > Â#define __put_user_nocheck(x, ptr, size)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ\
> > 
> > 
-- 
Ben Hutchings
If more than one person is responsible for a bug, no one is at fault.

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