linux-kernel - Re: [tip: objtool/urgent] objtool, media: dib8000: Prevent divide-by-zero in dib8000_set

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Message-ID: <20250326064239.5194fdc8@sal.lan>
Date: Wed, 26 Mar 2025 06:42:39 +0800
From: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To: "tip-bot2 for Josh Poimboeuf" <tip-bot2@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org, kernel
 test robot <lkp@...el.com>, Josh Poimboeuf <jpoimboe@...nel.org>, Ingo
 Molnar <mingo@...nel.org>, Mauro Carvalho Chehab <mchehab@...nel.org>,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org
Subject: Re: [tip: objtool/urgent] objtool, media: dib8000: Prevent
 divide-by-zero in dib8000_set_dds()

Em Tue, 25 Mar 2025 22:09:58 -0000
"tip-bot2 for Josh Poimboeuf" <tip-bot2@...utronix.de> escreveu:

> The following commit has been merged into the objtool/urgent branch of tip:
> 
> Commit-ID:     e63d465f59011dede0a0f1d21718b59a64c3ff5c
> Gitweb:        https://git.kernel.org/tip/e63d465f59011dede0a0f1d21718b59a64c3ff5c
> Author:        Josh Poimboeuf <jpoimboe@...nel.org>
> AuthorDate:    Mon, 24 Mar 2025 14:56:06 -07:00
> Committer:     Ingo Molnar <mingo@...nel.org>
> CommitterDate: Tue, 25 Mar 2025 23:00:15 +01:00
> 
> objtool, media: dib8000: Prevent divide-by-zero in dib8000_set_dds()
> 
> If dib8000_set_dds()'s call to dib8000_read32() returns zero, the result
> is a divide-by-zero.  Prevent that from happening.
> 
> Fixes the following warning with an UBSAN kernel:
> 
>   drivers/media/dvb-frontends/dib8000.o: warning: objtool: dib8000_tune() falls through to next function dib8096p_cfg_DibRx()
> 
> Fixes: 173a64cb3fcf ("[media] dib8000: enhancement")
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Link: https://lore.kernel.org/r/bd1d504d930ae3f073b1e071bcf62cae7708773c.1742852847.git.jpoimboe@kernel.org
> Closes: https://lore.kernel.org/r/202503210602.fvH5DO1i-lkp@intel.com/
> ---
>  drivers/media/dvb-frontends/dib8000.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/dvb-frontends/dib8000.c b/drivers/media/dvb-frontends/dib8000.c
> index 2f51659..cfe59c3 100644
> --- a/drivers/media/dvb-frontends/dib8000.c
> +++ b/drivers/media/dvb-frontends/dib8000.c
> @@ -2701,8 +2701,11 @@ static void dib8000_set_dds(struct dib8000_state *state, s32 offset_khz)
>  	u8 ratio;
>  
>  	if (state->revision == 0x8090) {
> +		u32 internal = dib8000_read32(state, 23) / 1000;
> +
>  		ratio = 4;
> -		unit_khz_dds_val = (1<<26) / (dib8000_read32(state, 23) / 1000);
> +
> +		unit_khz_dds_val = (1<<26) / (internal ?: 1);

This is theoretical, as in practice dib8096 won't likely be tuning
if reading this register would return zero, but at least for my
eyes, it would sound better to set unit_khz_dds_val to 1 internal
is zero, instead of 1<<26. 

>  		if (offset_khz < 0)
>  			dds = (1 << 26) - (abs_offset_khz * unit_khz_dds_val);
>  		else


Regards,
Mauro