This is a note to let you know that I've just added the patch titled auxdisplay: img-ascii-lcd: Fix lock-up when displaying empty string to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: auxdisplay-img-ascii-lcd-fix-lock-up-when-displaying.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit a1530a451a7c3d504ece046a0f2d565ff0676dc3 Author: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> Date: Tue Oct 19 16:45:02 2021 +0200 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: 0cad855fbd083ee5 ("auxdisplay: img-ascii-lcd: driver for simple ASCII LCD displays") Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/auxdisplay/img-ascii-lcd.c b/drivers/auxdisplay/img-ascii-lcd.c index 834509506ef64..c4bc6723acfa5 100644 --- a/drivers/auxdisplay/img-ascii-lcd.c +++ b/drivers/auxdisplay/img-ascii-lcd.c @@ -284,6 +284,16 @@ 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;