From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793214686; b=3IzPyPs8g8BniUQQ5AZg36Mk8XPG+5VPR89au8p4Jh0fIGSKn3JQInESj2ZTpECDKkAv UquC1mkUrqISN58i0rDJwaCxFLBxkQ8DRT8+BCh7/+HUn5d2gZXJXWWOmf/w+0nalA6EQ 0mUr9IwWtiS/7ZrObDCQkLrDuEVZ8qw2YE69FzcxU1m/ydY1Y87Qz+LziMIRAf6YtrUK+ X3ckJ08OklyJei8c0aOzsRUclzcN5ShKesyh/NIzEeiOFuYYbbJMM15PCcXR/EqYhggzD 9VQP0jcyu0tyhS45adCl/7A+nD8Q5R+QIos8hjY7wdpo0THryQ0jKRwtTtue/S2W7vw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793214686; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=xfc8NQucg1kPtyhTfEdIC5wzWe9R4iDFJsTmXD9HQPo=; b=dKdyLJgoG8Xo6xNTZs0QTFfWHSzDOX/akk/1VunOqH6qBE7VrQKbv/ZvrJnTWH96yDUS 0ugysUhTAmNLXRJcCgV1HEyvLX71fk3lrQbGieHyV2kDUPbJDWlOOXh7e3gAJ4sxjROQY ry4MrdEgIz82/auOd4hy4FXuYcMgF4uGWjoIMp4jwXNDWVEmDyvxRTLWv5TcWH296O0UO JeWN7hGo38tG9pYrnT0JCsVgFpda2nVbUFhqnJiZULqJyjDJWcIpy41696D3WH3q86NYb 1ExvNSa/gjYBWv8j//4gzHsmCRnbvjHJ0EWjOX8wKJb8Xd9aYqBJ0syAh/Oo5pttiNw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=YnHLB71j; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 62131606A31D; Wed, 28 Oct 2026 19:11:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=YnHLB71j Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7149B1F01829; Wed, 28 Oct 2026 19:11:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793214686; bh=xfc8NQucg1kPtyhTfEdIC5wzWe9R4iDFJsTmXD9HQPo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=YnHLB71jMuudDIylTCgRgVnmyMZ9AacJutA880Voqg9bmkW1bCZRCg2Vdv0Uy8nRF gA+bswRkFJW+nJAsDgQPBg01NufDbZ7N/ia3FxsJpXUIG58psiIQwCLm1/OUze2QgE CM+HPJyY8Z1XBCB/WYv+bJSexaf2roXKg7PEvDyA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jiayuan Chen , stable , Sasha Levin Subject: [PATCH 6.1 0944/1887] serial: core: fix infinite loop in handle_tx() for PORT_UNKNOWN Date: Wed, 28 Oct 2026 17:50:40 +0100 Message-ID: <20261028170520.892488146@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170459.200466217@linuxfoundation.org> References: <20261028170459.200466217@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen [ Upstream commit 455ce986fa356ff43a43c0d363ba95fa152f21d5 ] uart_write_room() and uart_write() behave inconsistently when xmit_buf is NULL (which happens for PORT_UNKNOWN ports that were never properly initialized): - uart_write_room() returns kfifo_avail() which can be > 0 - uart_write() checks xmit_buf and returns 0 if NULL This inconsistency causes an infinite loop in drivers that rely on tty_write_room() to determine if they can write: while (tty_write_room(tty) > 0) { written = tty->ops->write(...); // written is always 0, loop never exits } For example, caif_serial's handle_tx() enters an infinite loop when used with PORT_UNKNOWN serial ports, causing system hangs. Fix by making uart_write_room() also check xmit_buf and return 0 if it's NULL, consistent with uart_write(). Reproducer: https://gist.github.com/mrpre/d9a694cc0e19828ee3bc3b37983fde13 Signed-off-by: Jiayuan Chen Cc: stable Link: https://patch.msgid.link/20260204074327.226165-1-jiayuan.chen@linux.dev Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/serial_core.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index dafbd24b91484..4b035292a3840 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -610,7 +610,10 @@ static unsigned int uart_write_room(struct tty_struct *tty) unsigned int ret; port = uart_port_lock(state, flags); - ret = uart_circ_chars_free(&state->xmit); + if (!state->xmit.buf) + ret = 0; + else + ret = uart_circ_chars_free(&state->xmit); uart_port_unlock(port, flags); return ret; } -- 2.53.0