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

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Message-ID: <20210414150810.GA19371@redhat.com>
Date:   Wed, 14 Apr 2021 17:08:10 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     He Zhe <zhe.he@...driver.com>, Paul Moore <paul@...l-moore.com>,
        Eric Paris <eparis@...hat.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ptrace: is_syscall_success: Add syscall return code
 handling for compat task

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.

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
>