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From: Stephen Boyd <>
To: Martin Blumenstingl <>,
	Martin Blumenstingl <>
Subject: Re: [PATCH RFC v1] clk: Fix potential NULL dereference in clk_fetch_parent_index()
Date: Thu, 15 Aug 2019 16:29:50 -0700
Message-ID: <> (raw)
In-Reply-To: <>

Quoting Martin Blumenstingl (2019-08-15 15:31:55)
> Don't compare the parent clock name with a NULL name in the
> clk_parent_map. This prevents a kernel crash when passing NULL
> core->parents[i].name to strcmp().
> An example which triggered this is a mux clock with four parents when
> each of them is referenced in the clock driver using
> clk_parent_data.fw_name and then calling clk_set_parent(clk, 3rd_parent)
> on this mux.
> In this case the first parent is also the HW default so
> core->parents[i].hw is populated when the clock is registered. Calling
> clk_set_parent(clk, 3rd_parent) will then go through all parents and
> skip the first parent because it's hw pointer doesn't match. For the
> second parent no hw pointer is cached yet and clk_core_get(core, 1)
> returns a non-matching pointer (which is correct because we are comparing
> the second with the third parent). Comparing the result of
> clk_core_get(core, 2) with the requested parent gives a match. However
> we don't reach this point because right after the clk_core_get(core, 1)
> mismatch the old code tried to !strcmp(parent->name, NULL) (where the
> second argument is actually core->parents[i].name, but that was never
> populated by the clock driver).
> Signed-off-by: Martin Blumenstingl <>
> ---
> I have seen the original crash when I was testing an MMC driver which
> is not upstream yet on v5.3-rc4. I'm not sure whether this fix is
> "correct" (it fixes the crash for me) or where to point the Fixes tag
> to, it may be one of:
> - fc0c209c147f ("clk: Allow parents to be specified without string names")
> - 1a079560b145 ("clk: Cache core in clk_fetch_parent_index() without names")
> This is meant to be applied on top of v5.3-rc4.

Ah ok. I thought that strcmp() would ignore NULL arguments, but
apparently not. I can apply this to clk-fixes.

  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-15 22:31 Martin Blumenstingl
2019-08-15 23:29 ` Stephen Boyd [this message]
2019-08-16  6:48   ` Martin Blumenstingl
2019-08-16 17:31     ` Stephen Boyd
2019-08-19  8:43       ` Neil Armstrong
2019-08-16 17:30 ` Stephen Boyd

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