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auxdisplay: img-ascii-lcd: Fix lock-up when displaying empty string

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[ 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: 0cad855fbd ("auxdisplay: img-ascii-lcd: driver for simple ASCII LCD displays")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Geert Uytterhoeven 2021-10-19 16:45:02 +02:00 committed by Greg Kroah-Hartman
parent 0e1709b2a0
commit a1d6a60ee0
1 changed files with 10 additions and 0 deletions
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10
drivers/auxdisplay/img-ascii-lcd.c
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@ -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;