diff mbox series

[v4] gpio: sim: fix an invalid __free() usage

Message ID 20230918145533.14642-1-brgl@bgdev.pl
State New
Headers show
Series [v4] gpio: sim: fix an invalid __free() usage | expand

Commit Message

Bartosz Golaszewski Sept. 18, 2023, 2:55 p.m. UTC 
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

gpio_sim_make_line_names() returns NULL or ERR_PTR() so we must not use
__free(kfree) on the returned address. Split this function into two, one
that determines the size of the "gpio-line-names" array to allocate and
one that actually sets the names at correct offsets. The allocation and
assignment of the managed pointer happens in between.

Fixes: 3faf89f27aab ("gpio: sim: simplify code with cleanup helpers")
Reported-by: Alexey Dobriyan <adobriyan@gmail.com>
Closes: https://lore.kernel.org/all/07c32bf1-6c1a-49d9-b97d-f0ae4a2b42ab@p183/
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
Linus,

I followed the pattern for determining the size of the line-names array
from your patch in the end but with a changed variable naming. If this is
fine, I'll queue it for fixes for the next rc.

Bart

v3 -> v4:
- simplify the line counting logic

v2 -> v3:
- restore the offset out-of-bounds checks

v1 -> v2:
- split the line name setting into two parts

 drivers/gpio/gpio-sim.c | 59 +++++++++++++++--------------------------
 1 file changed, 22 insertions(+), 37 deletions(-)

Comments

Linus Torvalds Sept. 23, 2023, 6:19 p.m. UTC | #1 
On Tue, 19 Sept 2023 at 03:49, Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> Nope, k*alloc*() returns ZERO or NULL on failure. That's what most developers
> are missing :-)

Absolutely not.

k*alloc() returns NULL on failure. Absolutely nothing else.

On *success*, it can return the special ZERO_SIZE_PTR. But that is
*not* a failure at all. It's very much a successful pointer.

Now, it's a pointer that you can't actually dereference, but that's
very much intentional. You can't dereference it, because you asked for
a zero-sized allocation. You got a zero-sized allocation.

But please never *ever* think it's a failure. It's very much not a
failure case, and it is very much intentional.

It's different from NULL exactly *because* it's successful, and
exactly so that you can write

     ptr = kmalloc(size);
     if (!ptr)
          return -ENOMEM;

without having to worry about the "size is zero" case.

The standard user-space "malloc()" library is misdesigned. Surprise
surprise. The kernel isn't.

                Linus
diff mbox series

Patch

diff --git a/drivers/gpio/gpio-sim.c b/drivers/gpio/gpio-sim.c
index 460389bb8e3f..b66abb55ef4d 100644
--- a/drivers/gpio/gpio-sim.c
+++ b/drivers/gpio/gpio-sim.c
@@ -718,52 +718,32 @@  gpio_sim_device_config_live_show(struct config_item *item, char *page)
 	return sprintf(page, "%c\n", live ? '1' : '0');
 }
 
-static char **gpio_sim_make_line_names(struct gpio_sim_bank *bank,
-				       unsigned int *line_names_size)
+static unsigned int gpio_sim_get_line_names_size(struct gpio_sim_bank *bank)
 {
-	unsigned int max_offset = 0;
-	bool has_line_names = false;
 	struct gpio_sim_line *line;
-	char **line_names;
+	unsigned int size = 0;
 
 	list_for_each_entry(line, &bank->line_list, siblings) {
-		if (line->offset >= bank->num_lines)
+		if (!line->name || (line->offset >= bank->num_lines))
 			continue;
 
-		if (line->name) {
-			if (line->offset > max_offset)
-				max_offset = line->offset;
-
-			/*
-			 * max_offset can stay at 0 so it's not an indicator
-			 * of whether line names were configured at all.
-			 */
-			has_line_names = true;
-		}
+		size = line->offset + 1;
 	}
 
-	if (!has_line_names)
-		/*
-		 * This is not an error - NULL means, there are no line
-		 * names configured.
-		 */
-		return NULL;
-
-	*line_names_size = max_offset + 1;
+	return size;
+}
 
-	line_names = kcalloc(*line_names_size, sizeof(*line_names), GFP_KERNEL);
-	if (!line_names)
-		return ERR_PTR(-ENOMEM);
+static void
+gpio_sim_set_line_names(struct gpio_sim_bank *bank, char **line_names)
+{
+	struct gpio_sim_line *line;
 
 	list_for_each_entry(line, &bank->line_list, siblings) {
-		if (line->offset >= bank->num_lines)
+		if (!line->name || (line->offset >= bank->num_lines))
 			continue;
 
-		if (line->name && (line->offset <= max_offset))
-			line_names[line->offset] = line->name;
+		line_names[line->offset] = line->name;
 	}
-
-	return line_names;
 }
 
 static void gpio_sim_remove_hogs(struct gpio_sim_device *dev)
@@ -867,7 +847,7 @@  gpio_sim_make_bank_swnode(struct gpio_sim_bank *bank,
 			  struct fwnode_handle *parent)
 {
 	struct property_entry properties[GPIO_SIM_PROP_MAX];
-	unsigned int prop_idx = 0, line_names_size = 0;
+	unsigned int prop_idx = 0, line_names_size;
 	char **line_names __free(kfree) = NULL;
 
 	memset(properties, 0, sizeof(properties));
@@ -878,14 +858,19 @@  gpio_sim_make_bank_swnode(struct gpio_sim_bank *bank,
 		properties[prop_idx++] = PROPERTY_ENTRY_STRING("gpio-sim,label",
 							       bank->label);
 
-	line_names = gpio_sim_make_line_names(bank, &line_names_size);
-	if (IS_ERR(line_names))
-		return ERR_CAST(line_names);
+	line_names_size = gpio_sim_get_line_names_size(bank);
+	if (line_names_size) {
+		line_names = kcalloc(line_names_size, sizeof(*line_names),
+				     GFP_KERNEL);
+		if (!line_names)
+			return ERR_PTR(-ENOMEM);
+
+		gpio_sim_set_line_names(bank, line_names);
 
-	if (line_names)
 		properties[prop_idx++] = PROPERTY_ENTRY_STRING_ARRAY_LEN(
 						"gpio-line-names",
 						line_names, line_names_size);
+	}
 
 	return fwnode_create_software_node(properties, parent);
 }