Re: Patch "signal/metag: Document a conflict with SI_USER with SIGFPE" has been added to the 4.15-stable tree

[ebiederm@xmission.com (Eric W. Biederman)]

<gregkh@linuxfoundation.org> writes:

> This is a note to let you know that I've just added the patch titled
>
>     signal/metag: Document a conflict with SI_USER with SIGFPE
>
> to the 4.15-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
>      signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch
> and it can be found in the queue-4.15 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.

The patch is a noop functionality wise so I don't see the point of
backporting it to stable.

Eric

> From foo@baz Mon Apr  9 10:16:32 CEST 2018
> From: "Eric W. Biederman" <ebiederm@xmission.com>
> Date: Tue, 1 Aug 2017 10:37:40 -0500
> Subject: signal/metag: Document a conflict with SI_USER with SIGFPE
>
> From: "Eric W. Biederman" <ebiederm@xmission.com>
>
>
> [ Upstream commit b80328be53c215346b153769267b38f531d89b4f ]
>
> Setting si_code to 0 results in a userspace seeing an si_code of 0.
> This is the same si_code as SI_USER.  Posix and common sense requires
> that SI_USER not be a signal specific si_code.  As such this use of 0
> for the si_code is a pretty horribly broken ABI.
>
> Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a
> value of __SI_KILL and now sees a value of SIL_KILL with the result
> hat uid and pid fields are copied and which might copying the si_addr
> field by accident but certainly not by design.  Making this a very
> flakey implementation.
>
> Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the
> appropriate fields will reliably be copied.
>
> Possible ABI fixes includee:
>   - Send the signal without siginfo
>   - Don't generate a signal
>   - Possibly assign and use an appropriate si_code
>   - Don't handle cases which can't happen
>
> Cc: James Hogan <james.hogan@imgtec.com>
> Cc: linux-metag@vger.kernel.org
> Ref: ac919f0883e5 ("metag: Traps")
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  arch/metag/include/uapi/asm/siginfo.h |    7 +++++++
>  arch/metag/kernel/traps.c             |    2 +-
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> --- a/arch/metag/include/uapi/asm/siginfo.h
> +++ b/arch/metag/include/uapi/asm/siginfo.h
> @@ -6,4 +6,11 @@
>  
>  #include <asm-generic/siginfo.h>
>  
> +/*
> + * SIGFPE si_codes
> + */
> +#ifdef __KERNEL__
> +#define FPE_FIXME      0       /* Broken dup of SI_USER */
> +#endif /* __KERNEL__ */
> +
>  #endif
> --- a/arch/metag/kernel/traps.c
> +++ b/arch/metag/kernel/traps.c
> @@ -735,7 +735,7 @@ TBIRES fpe_handler(TBIRES State, int Sig
>  	else if (error_state & TXSTAT_FPE_INEXACT_BIT)
>  		info.si_code = FPE_FLTRES;
>  	else
> -		info.si_code = 0;
> +		info.si_code = FPE_FIXME;
>  	info.si_errno = 0;
>  	info.si_addr = (__force void __user *)regs->ctx.CurrPC;
>  	force_sig_info(SIGFPE, &info, current);
>
>
> Patches currently in stable-queue which might be from ebiederm@xmission.com are
>
> queue-4.15/signal-metag-document-a-conflict-with-si_user-with-sigfpe.patch
> queue-4.15/signal-arm-document-conflicts-with-si_user-and-sigfpe.patch
> queue-4.15/signal-powerpc-document-conflicts-with-si_user-and-sigfpe-and-sigtrap.patch