linux-kernel - RE: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code handling for compat task

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Message-ID: <e2efffb879914176a2eae8b52a3c5c33@AcuMS.aculab.com>
Date:   Wed, 14 Apr 2021 16:17:02 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Oleg Nesterov' <oleg@...hat.com>, He Zhe <zhe.he@...driver.com>,
        "Paul Moore" <paul@...l-moore.com>, Eric Paris <eparis@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code
 handling for compat task

From: Oleg Nesterov
> Sent: 14 April 2021 16:08
> 
> Add audit maintainers...
> 
> On 04/14, He Zhe wrote:
> >
> > When 32-bit userspace application is running on 64-bit kernel, the 32-bit
> > syscall return code would be changed from u32 to u64 in regs_return_value
> > and then changed to s64. Hence the negative return code would be treated
> > as a positive number and results in a non-error in, for example, audit
> > like below.
> 
> Sorry, can understand. At least on x86_64 even the 32-bit syscall returns
> long, not u32.
> 
> Hmm. And afaics on x86 is_compat_task() is only defined if !CONFIG_COMPAT,
> so this patch looks wrong anyway.

And, as with the other patch a x64_64 64bit process can make both types
of 32bit system call - so it needs to depend on the system call entry type
not any type of the task.

	David

> 
> Oleg.
> 
> > type=SYSCALL msg=audit(1611110715.887:582): arch=40000028 syscall=322
> > success=yes exit=4294967283
> >
> > This patch forces the u32->s32->s64 for compat tasks.
> >
> > Signed-off-by: He Zhe <zhe.he@...driver.com>
> > ---
> >  include/linux/ptrace.h | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
> > index b5ebf6c01292..bc3056fff8a6 100644
> > --- a/include/linux/ptrace.h
> > +++ b/include/linux/ptrace.h
> > @@ -260,7 +260,9 @@ static inline void ptrace_release_task(struct task_struct *task)
> >   * is an error value.  On some systems like ia64 and powerpc they have different
> >   * indicators of success/failure and must define their own.
> >   */
> > -#define is_syscall_success(regs) (!IS_ERR_VALUE((unsigned long)(regs_return_value(regs))))
> > +#define is_syscall_success(regs) (!IS_ERR_VALUE(is_compat_task() ? \
> > +	(unsigned long)(s64)(s32)(regs_return_value(regs)) : \
> > +	(unsigned long)(regs_return_value(regs))))
> >  #endif
> >
> >  /*
> > --
> > 2.17.1
> >

-
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