[PATCH] tty: vt: Check for NULL pointer after calling kzalloc

[PATCH] tty: vt: Check for NULL pointer after calling kzalloc

[Jiasheng Jiang]

As the potential failure of the allocation, the kzalloc() will return
NULL pointer.
Therefore, it should be better to check it in order to avoid the
dereference of the NULL pointer.
When it fails, we should free all the allocated memory and return error
number.
To make the code more clear, I use the 'err_free', like how
vc_allocate() deals with the allocation failure.

Fixes: a5f4f52e8211 ("vt: use kzalloc() instead of the bootmem allocator")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
---
 drivers/tty/vt/vt.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index f8c87c4d7399..343fa6fffc18 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -3519,11 +3519,17 @@ static int __init con_init(void)
 
 	for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
 		vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data), GFP_NOWAIT);
+		if (!vc)
+			goto err_free;
+
 		INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
 		tty_port_init(&vc->port);
 		visual_init(vc, currcons, 1);
 		/* Assuming vc->vc_{cols,rows,screenbuf_size} are sane here. */
 		vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
+		if (!vc->vc_screenbuf)
+			goto err_free_vc;
+
 		vc_init(vc, vc->vc_rows, vc->vc_cols,
 			currcons || !vc->vc_sw->con_save_screen);
 	}
@@ -3545,6 +3551,19 @@ static int __init con_init(void)
 	register_console(&vt_console_driver);
 #endif
 	return 0;
+err_free_vc:
+	visual_deinit(vc);
+	kfree(vc);
+	vc_cons[currcons].d = NULL;
+err_free:
+	for (i = 0; i < currcons; i++) {
+		kfree(vc_cons[currcons].d->vc_screenbuf);
+		visual_deinit(vc_cons[currcons].d);
+		kfree(vc_cons[currcons].d);
+		vc_cons[currcons].d = NULL;
+	}
+	console_unlock();
+	return -ENOMEM;
 }
 console_initcall(con_init);
 
-- 
2.25.1

Re: [PATCH] tty: vt: Check for NULL pointer after calling kzalloc

[Jiri Slaby]

On 21. 01. 22, 7:53, Jiasheng Jiang wrote:
> As the potential failure of the allocation, the kzalloc() will return
> NULL pointer.
> Therefore, it should be better to check it in order to avoid the
> dereference of the NULL pointer.
> When it fails, we should free all the allocated memory and return error
> number.
> To make the code more clear, I use the 'err_free', like how
> vc_allocate() deals with the allocation failure.

https://lore.kernel.org/all/X+CRTqDQwVYSZQBi@kroah.com/

> Fixes: a5f4f52e8211 ("vt: use kzalloc() instead of the bootmem allocator")
> Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
> ---
>   drivers/tty/vt/vt.c | 19 +++++++++++++++++++
>   1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index f8c87c4d7399..343fa6fffc18 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -3519,11 +3519,17 @@ static int __init con_init(void)
>   
>   	for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
>   		vc_cons[currcons].d = vc = kzalloc(sizeof(struct vc_data), GFP_NOWAIT);
> +		if (!vc)
> +			goto err_free;
> +
>   		INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
>   		tty_port_init(&vc->port);
>   		visual_init(vc, currcons, 1);
>   		/* Assuming vc->vc_{cols,rows,screenbuf_size} are sane here. */
>   		vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
> +		if (!vc->vc_screenbuf)
> +			goto err_free_vc;
> +
>   		vc_init(vc, vc->vc_rows, vc->vc_cols,
>   			currcons || !vc->vc_sw->con_save_screen);
>   	}
> @@ -3545,6 +3551,19 @@ static int __init con_init(void)
>   	register_console(&vt_console_driver);
>   #endif
>   	return 0;
> +err_free_vc:
> +	visual_deinit(vc);
> +	kfree(vc);
> +	vc_cons[currcons].d = NULL;
> +err_free:
> +	for (i = 0; i < currcons; i++) {
> +		kfree(vc_cons[currcons].d->vc_screenbuf);
> +		visual_deinit(vc_cons[currcons].d);
> +		kfree(vc_cons[currcons].d);
> +		vc_cons[currcons].d = NULL;
> +	}
> +	console_unlock();
> +	return -ENOMEM;
>   }
>   console_initcall(con_init);
>   


-- 
js

Re: [PATCH] tty: vt: Check for NULL pointer after calling kzalloc

[Greg KH]

On Fri, Jan 21, 2022 at 02:53:20PM +0800, Jiasheng Jiang wrote:
> As the potential failure of the allocation, the kzalloc() will return
> NULL pointer.
> Therefore, it should be better to check it in order to avoid the
> dereference of the NULL pointer.
> When it fails, we should free all the allocated memory and return error
> number.
> To make the code more clear, I use the 'err_free', like how
> vc_allocate() deals with the allocation failure.
> 
> Fixes: a5f4f52e8211 ("vt: use kzalloc() instead of the bootmem allocator")
> Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
> ---
>  drivers/tty/vt/vt.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)

Please note that your patches are being ignored by my email systems (I
saw this because Jiri responded to it.)  I recommend at this point in
time that all other kernel subsystem maintainers also ignore them until
you get some more experience and provide changes that work correctly and
are actually tested.

good luck,

greg k-h