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SubjectRe: [PATCH][next] gpio: sim: Fix dereference of free'd pointer config
On Tue, Apr 27, 2021 at 12:24 PM Colin King <colin.king@canonical.com> wrote:
>
> From: Colin Ian King <colin.king@canonical.com>
>
> The error return of config->id dereferences the kfree'd object config.
> Fix this by using a temporary variable for the id to avoid this issue.
>
> Addresses-Coverity: ("Read from pointer aftyer free")
> Fixes: a49d14276ac4 ("gpio: sim: allocate IDA numbers earlier")
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
> drivers/gpio/gpio-sim.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpio-sim.c b/drivers/gpio/gpio-sim.c
> index 2e2e6399e453..7bba5783a043 100644
> --- a/drivers/gpio/gpio-sim.c
> +++ b/drivers/gpio/gpio-sim.c
> @@ -751,8 +751,10 @@ gpio_sim_config_make_item(struct config_group *group, const char *name)
>
> config->id = ida_alloc(&gpio_sim_ida, GFP_KERNEL);
> if (config->id < 0) {
> + int id = config->id;
> +
> kfree(config);
> - return ERR_PTR(config->id);
> + return ERR_PTR(id);
> }
>
> config_item_init_type_name(&config->item, name,
> --
> 2.30.2
>

Thanks! Can you do something like this:

diff --git a/drivers/gpio/gpio-sim.c b/drivers/gpio/gpio-sim.c
index 2e2e6399e453..b21541c0b700 100644
--- a/drivers/gpio/gpio-sim.c
+++ b/drivers/gpio/gpio-sim.c
@@ -744,20 +744,22 @@ static struct config_item *
gpio_sim_config_make_item(struct config_group *group, const char *name)
{
struct gpio_sim_chip_config *config;
+ int id;

config = kzalloc(sizeof(*config), GFP_KERNEL);
if (!config)
return ERR_PTR(-ENOMEM);

- config->id = ida_alloc(&gpio_sim_ida, GFP_KERNEL);
- if (config->id < 0) {
+ id = ida_alloc(&gpio_sim_ida, GFP_KERNEL);
+ if (id < 0) {
kfree(config);
- return ERR_PTR(config->id);
+ return ERR_PTR(id);
}

config_item_init_type_name(&config->item, name,
&gpio_sim_chip_config_type);
config->num_lines = 1;
+ config->id = id;
mutex_init(&config->lock);

return &config->item;

I think this looks more elegant without the local variable inside the if.

Bart

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