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Commit 05d9522a authored by Geert Uytterhoeven's avatar Geert Uytterhoeven Committed by Greg Kroah-Hartman
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auxdisplay: img-ascii-lcd: Fix lock-up when displaying empty string 



[ Upstream commit afcb5a811ff3ab3969f09666535eb6018a160358 ]

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: 0cad855f ("auxdisplay: img-ascii-lcd: driver for simple ASCII LCD displays")
Signed-off-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 311d7eb5

drivers/auxdisplay/img-ascii-lcd.c

+10 −0
Original line number Diff line number Diff line
@@ -283,6 +283,16 @@ 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;