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mmc: pwrseq: Use kmalloc_array instead of stack VLA

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The use of stack Variable Length Arrays needs to be avoided, as they
can be a vector for stack exhaustion, which can be both a runtime bug
(kernel Oops) or a security flaw (overwriting memory beyond the
stack). Also, in general, as code evolves it is easy to lose track of
how big a VLA can get. Thus, we can end up having runtime failures
that are hard to debug. As part of the directive[1] to remove all VLAs
from the kernel, and build with -Wvla.

Currently driver is using a VLA declared using the number of descriptors.  This
array is used to store integer values and is later used as an argument to
`gpiod_set_array_value_cansleep()` This can be avoided by using
`kmalloc_array()` to allocate memory for the array of integer values.  Memory is
free'd before return from function.

>From the code it appears that it is safe to sleep so we can use GFP_KERNEL
(based _cansleep() suffix of function `gpiod_set_array_value_cansleep()`.

It can be expected that this patch will result in a small increase in overhead
due to the use of `kmalloc_array()`

[1] https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
This commit is contained in:
Tobin C. Harding 2018-03-26 17:33:14 +11:00 committed by Ulf Hansson
parent 57aac3377f
commit 486e666136
1 changed files with 9 additions and 5 deletions
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14
drivers/mmc/core/pwrseq_simple.c
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@ -40,14 +40,18 @@ static void mmc_pwrseq_simple_set_gpios_value(struct mmc_pwrseq_simple *pwrseq,
struct gpio_descs *reset_gpios = pwrseq->reset_gpios;
if (!IS_ERR(reset_gpios)) {
int i;
int values[reset_gpios->ndescs];
int i, *values;
int nvalues = reset_gpios->ndescs;
for (i = 0; i < reset_gpios->ndescs; i++)
values = kmalloc_array(nvalues, sizeof(int), GFP_KERNEL);
if (!values)
return;
for (i = 0; i < nvalues; i++)
values[i] = value;
gpiod_set_array_value_cansleep(
reset_gpios->ndescs, reset_gpios->desc, values);
gpiod_set_array_value_cansleep(nvalues, reset_gpios->desc, values);
kfree(values);
}
}