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a65d4bac GKH |
1 | From foo@baz Sat Jul 28 10:25:26 CEST 2018 |
2 | From: "Tobin C. Harding" <me@tobin.cc> | |
3 | Date: Mon, 26 Mar 2018 17:33:14 +1100 | |
4 | Subject: mmc: pwrseq: Use kmalloc_array instead of stack VLA | |
5 | ||
6 | From: "Tobin C. Harding" <me@tobin.cc> | |
7 | ||
8 | [ Upstream commit 486e6661367b40f927aadbed73237693396cbf94 ] | |
9 | ||
10 | The use of stack Variable Length Arrays needs to be avoided, as they | |
11 | can be a vector for stack exhaustion, which can be both a runtime bug | |
12 | (kernel Oops) or a security flaw (overwriting memory beyond the | |
13 | stack). Also, in general, as code evolves it is easy to lose track of | |
14 | how big a VLA can get. Thus, we can end up having runtime failures | |
15 | that are hard to debug. As part of the directive[1] to remove all VLAs | |
16 | from the kernel, and build with -Wvla. | |
17 | ||
18 | Currently driver is using a VLA declared using the number of descriptors. This | |
19 | array is used to store integer values and is later used as an argument to | |
20 | `gpiod_set_array_value_cansleep()` This can be avoided by using | |
21 | `kmalloc_array()` to allocate memory for the array of integer values. Memory is | |
22 | free'd before return from function. | |
23 | ||
24 | >From the code it appears that it is safe to sleep so we can use GFP_KERNEL | |
25 | (based _cansleep() suffix of function `gpiod_set_array_value_cansleep()`. | |
26 | ||
27 | It can be expected that this patch will result in a small increase in overhead | |
28 | due to the use of `kmalloc_array()` | |
29 | ||
30 | [1] https://lkml.org/lkml/2018/3/7/621 | |
31 | ||
32 | Signed-off-by: Tobin C. Harding <me@tobin.cc> | |
33 | Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> | |
34 | Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> | |
35 | Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> | |
36 | --- | |
37 | drivers/mmc/core/pwrseq_simple.c | 14 +++++++++----- | |
38 | 1 file changed, 9 insertions(+), 5 deletions(-) | |
39 | ||
40 | --- a/drivers/mmc/core/pwrseq_simple.c | |
41 | +++ b/drivers/mmc/core/pwrseq_simple.c | |
42 | @@ -40,14 +40,18 @@ static void mmc_pwrseq_simple_set_gpios_ | |
43 | struct gpio_descs *reset_gpios = pwrseq->reset_gpios; | |
44 | ||
45 | if (!IS_ERR(reset_gpios)) { | |
46 | - int i; | |
47 | - int values[reset_gpios->ndescs]; | |
48 | + int i, *values; | |
49 | + int nvalues = reset_gpios->ndescs; | |
50 | ||
51 | - for (i = 0; i < reset_gpios->ndescs; i++) | |
52 | + values = kmalloc_array(nvalues, sizeof(int), GFP_KERNEL); | |
53 | + if (!values) | |
54 | + return; | |
55 | + | |
56 | + for (i = 0; i < nvalues; i++) | |
57 | values[i] = value; | |
58 | ||
59 | - gpiod_set_array_value_cansleep( | |
60 | - reset_gpios->ndescs, reset_gpios->desc, values); | |
61 | + gpiod_set_array_value_cansleep(nvalues, reset_gpios->desc, values); | |
62 | + kfree(values); | |
63 | } | |
64 | } | |
65 |