[PATCH v4 01/15] clk: qcom: rcg2: Don't crash if our parent can't be found; return an error

Douglas Anderson
2020-02-03T18:33:24Z

When I got my clock parenting slightly wrong I ended up with a crash
that looked like this:

Unable to handle kernel NULL pointer dereference at virtual
address 0000000000000000
...
pc : clk_hw_get_rate+0x14/0x44
...
Call trace:
clk_hw_get_rate+0x14/0x44
_freq_tbl_determine_rate+0x94/0xfc
clk_rcg2_determine_rate+0x2c/0x38
clk_core_determine_round_nolock+0x4c/0x88
clk_core_round_rate_nolock+0x6c/0xa8
clk_core_round_rate_nolock+0x9c/0xa8
clk_core_set_rate_nolock+0x70/0x180
clk_set_rate+0x3c/0x6c
of_clk_set_defaults+0x254/0x360
platform_drv_probe+0x28/0xb0
really_probe+0x120/0x2dc
driver_probe_device+0x64/0xfc
device_driver_attach+0x4c/0x6c
__driver_attach+0xac/0xc0
bus_for_each_dev+0x84/0xcc
driver_attach+0x2c/0x38
bus_add_driver+0xfc/0x1d0
driver_register+0x64/0xf8
__platform_driver_register+0x4c/0x58
msm_drm_register+0x5c/0x60
...

It turned out that clk_hw_get_parent_by_index() was returning NULL and
we weren't checking. Let's check it so that we don't crash.

Fixes: ac269395cdd8 ("clk: qcom: Convert to clk_hw based provider APIs")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
---
I haven't gone back and tried to reproduce this same crash on older
kernels, but I'll put the blame on commit ac269395cdd8 ("clk: qcom:
Convert to clk_hw based provider APIs"). Before that if we got a NULL
parent back it was fine and dandy since a NULL "struct clk" is valid
to use but a NULL "struct clk_hw" is not.

Changes in v4: None
Changes in v3:
- Add Matthias tag.

Changes in v2:
- Patch ("clk: qcom: rcg2: Don't crash...") new for v2.

drivers/clk/qcom/clk-rcg2.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
index da045b200def..9098001ac805 100644
--- a/drivers/clk/qcom/clk-rcg2.c
+++ b/drivers/clk/qcom/clk-rcg2.c
@@ -218,6 +218,9 @@ static int _freq_tbl_determine_rate(struct clk_hw *hw, const struct freq_tbl *f,

clk_flags = clk_hw_get_flags(hw);
p = clk_hw_get_parent_by_index(hw, index);
+ if (!p)
+ return -EINVAL;
+
if (clk_flags & CLK_SET_RATE_PARENT) {
rate = f->freq;
if (f->pre_div) {
--
2.25.0.341.g760bfbb309-goog