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From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Robin van der Gracht <robin@protonic.nl>,
	Rob Herring <robh+dt@kernel.org>, Miguel Ojeda <ojeda@kernel.org>,
	Paul Burton <paulburton@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Pavel Machek <pavel@ucw.cz>, Marek Behun <marek.behun@nic.cz>
Cc: devicetree@vger.kernel.org, linux-leds@vger.kernel.org,
	linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
	Geert Uytterhoeven <geert@linux-m68k.org>
Subject: [PATCH v4 03/19] auxdisplay: img-ascii-lcd: Fix lock-up when displaying empty string
Date: Tue, 27 Jul 2021 16:04:43 +0200	[thread overview]
Message-ID: <20210727140459.3767788-4-geert@linux-m68k.org> (raw)
In-Reply-To: <20210727140459.3767788-1-geert@linux-m68k.org>

While writing an empty string to a device attribute is a no-op, and thus
does not need explicit safeguards, the user can still write a single
newline to an attribute file:

    echo > .../message

If that happens, img_ascii_lcd_display() trims the newline, yielding an
empty string, and causing an infinite loop in img_ascii_lcd_scroll().

Fix this by adding a check for empty strings.  Clear the display in case
one is encountered.

Fixes: 0cad855fbd083ee5 ("auxdisplay: img-ascii-lcd: driver for simple ASCII LCD displays")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Untested with img-ascii-lcd, but triggered with my initial version of
linedisp.

v4:
  - No changes,

v3:
  - No changes,

v2:
  - No changes.
---
 drivers/auxdisplay/img-ascii-lcd.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/auxdisplay/img-ascii-lcd.c b/drivers/auxdisplay/img-ascii-lcd.c
index 1cce409ce5cacbc8..e33ce0151cdfd150 100644
--- a/drivers/auxdisplay/img-ascii-lcd.c
+++ b/drivers/auxdisplay/img-ascii-lcd.c
@@ -280,6 +280,16 @@ static int img_ascii_lcd_display(struct img_ascii_lcd_ctx *ctx,
 	if (msg[count - 1] == '\n')
 		count--;
 
+	if (!count) {
+		/* clear the LCD */
+		devm_kfree(&ctx->pdev->dev, ctx->message);
+		ctx->message = NULL;
+		ctx->message_len = 0;
+		memset(ctx->curr, ' ', ctx->cfg->num_chars);
+		ctx->cfg->update(ctx);
+		return 0;
+	}
+
 	new_msg = devm_kmalloc(&ctx->pdev->dev, count + 1, GFP_KERNEL);
 	if (!new_msg)
 		return -ENOMEM;
-- 
2.25.1


  parent reply	other threads:[~2021-07-27 14:07 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 14:04 [PATCH v4 00/19] auxdisplay: ht16k33: Add character display support Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 01/19] uapi: Add <linux/map_to_14segment.h> Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 02/19] dt-bindings: auxdisplay: ht16k33: Document Adafruit segment displays Geert Uytterhoeven
2021-08-02 20:40   ` Rob Herring
2021-07-27 14:04 ` Geert Uytterhoeven [this message]
2021-07-27 14:04 ` [PATCH v4 04/19] auxdisplay: img-ascii-lcd: Add helper variable dev Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 05/19] auxdisplay: img-ascii-lcd: Convert device attribute to sysfs_emit() Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 06/19] auxdisplay: Extract character line display core support Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 07/19] auxdisplay: linedisp: Use kmemdup_nul() helper Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 08/19] auxdisplay: linedisp: Add support for changing scroll rate Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 09/19] auxdisplay: ht16k33: Connect backlight to fbdev Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 10/19] auxdisplay: ht16k33: Use HT16K33_FB_SIZE in ht16k33_initialize() Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 11/19] auxdisplay: ht16k33: Remove unneeded error check in keypad probe() Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 12/19] auxdisplay: ht16k33: Convert to simple i2c probe function Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 13/19] auxdisplay: ht16k33: Add helper variable dev Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 14/19] auxdisplay: ht16k33: Move delayed work Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 15/19] auxdisplay: ht16k33: Extract ht16k33_brightness_set() Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 16/19] auxdisplay: ht16k33: Extract frame buffer probing Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 17/19] auxdisplay: ht16k33: Add support for segment displays Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 18/19] dt-bindings: auxdisplay: ht16k33: Document LED subnode Geert Uytterhoeven
2021-07-27 14:04 ` [PATCH v4 19/19] auxdisplay: ht16k33: Add LED support Geert Uytterhoeven
2021-07-27 21:05   ` Randy Dunlap
2021-07-28  7:39     ` Geert Uytterhoeven

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