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Mon, 26 Apr 2021 16:15:24 GMT Received: from pps.reinject (localhost [127.0.0.1]) by aserp3030.oracle.com with ESMTP id 3849cddpvc-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 26 Apr 2021 16:15:24 +0000 Received: from aserp3030.oracle.com (aserp3030.oracle.com [127.0.0.1]) by pps.reinject (8.16.0.36/8.16.0.36) with SMTP id 13QGFNnN017302; Mon, 26 Apr 2021 16:15:23 GMT Received: from t460.home (dhcp-10-175-63-42.vpn.oracle.com [10.175.63.42]) by aserp3030.oracle.com with ESMTP id 3849cddprr-1; Mon, 26 Apr 2021 16:15:23 +0000 From: Vegard Nossum To: Greg Kroah-Hartman , linux-serial@vger.kernel.org, syzbot+4c7f1a69dfe24c6b3aeb@syzkaller.appspotmail.com, syzbot+92f32d4e21fb246d31a2@syzkaller.appspotmail.com Cc: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, Vegard Nossum , Peter Hurley , Caleb Connolly Subject: [PATCH] serial: 8250: fix NULL pointer dereference in serial8250_do_startup() Date: Mon, 26 Apr 2021 18:14:33 +0200 Message-Id: <20210426161433.20829-1-vegard.nossum@oracle.com> X-Mailer: git-send-email 2.16.1.72.g5be1f00a9.dirty In-Reply-To: <00000000000044a65205994a7e13@google.com> References: <00000000000044a65205994a7e13@google.com> X-Proofpoint-ORIG-GUID: yNUetMbxG64O1HiQf2pPLo7cT1Bj577S X-Proofpoint-GUID: yNUetMbxG64O1HiQf2pPLo7cT1Bj577S X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=9966 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 spamscore=0 phishscore=0 clxscore=1011 suspectscore=0 lowpriorityscore=0 mlxlogscore=999 mlxscore=0 adultscore=0 malwarescore=0 impostorscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104060000 definitions=main-2104260123 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Syzbot reported a crash, here reproduced on a recent mainline kernel: BUG: kernel NULL pointer dereference, address: 0000000000000005 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 120cf067 P4D 120cf067 PUD 135d4067 PMD 0 Oops: 0000 [#1] PREEMPT SMP KASAN CPU: 2 PID: 4830 Comm: a.out Not tainted 5.12.0-rc7+ #209 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014 RIP: 0010:mem16_serial_in+0x83/0xa0 [...] Call Trace: serial8250_do_startup+0x475/0x1e40 serial8250_startup+0x5c/0x80 uart_startup+0x360/0x870 uart_set_info_user+0x13a3/0x1c30 tty_ioctl+0x711/0x14f0 __x64_sys_ioctl+0x193/0x200 do_syscall_64+0x2d/0x70 entry_SYSCALL_64_after_hwframe+0x44/0xae A more readable reproducer is: #include #include #include #ifndef SERIAL_IO_MEM16 #define SERIAL_IO_MEM16 7 #endif int main(int argc, char *argv[]) { int fd = open("/dev/ttyS3", O_RDONLY); struct serial_struct ss = {}; ss.type = 0x10; ss.baud_base = 0x7fffffff; ss.io_type = SERIAL_IO_MEM16; ioctl(fd, TIOCSSERIAL, &ss); return 0; } ioctl(TIOCSSERIAL) attempts to configure the serial port, but when requesting io_type SERIAL_IO_MEM*/UPIO_MEM* it goes on to dereference ->membase in serial8250_do_startup(). I propose this fix, which will fail validation of the TIOCSSERIAL request if you request a memory-based or io-based io_type when the underlying port has no valid ->membase or ->iobase, respectively. As far as I can tell, this driver was written to support being able to switch between the two IO types for a given port (assuming the underlying driver supports it); see serial8250_do_startup()/set_io_from_upio(). I'm also adding a couple of WARN_ON_ONCE()s which are technically redundant, but which could help somebody else if they come across a similar issue in the future. Reported-by: syzbot+4c7f1a69dfe24c6b3aeb@syzkaller.appspotmail.com Cc: Peter Hurley Cc: Greg Kroah-Hartman Cc: linux-serial@vger.kernel.org Cc: Caleb Connolly Signed-off-by: Vegard Nossum --- drivers/tty/serial/8250/8250_port.c | 43 +++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index b0af13074cd36..aec3abff8e48e 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -455,6 +455,33 @@ static void io_serial_out(struct uart_port *p, int offset, int value) static int serial8250_default_handle_irq(struct uart_port *port); +static int needs_membase(int iotype) +{ + switch (iotype) { + case UPIO_MEM: + case UPIO_MEM16: + case UPIO_MEM32: + case UPIO_MEM32BE: +#ifdef CONFIG_SERIAL_8250_RT288X + case UPIO_AU: +#endif + return 1; + } + + return 0; +} + +static int needs_iobase(int iotype) +{ + switch (iotype) { + case UPIO_HUB6: + case UPIO_PORT: + return 1; + } + + return 0; +} + static void set_io_from_upio(struct uart_port *p) { struct uart_8250_port *up = up_to_u8250p(p); @@ -2151,6 +2178,11 @@ int serial8250_do_startup(struct uart_port *port) unsigned char lsr, iir; int retval; + if (WARN_ON_ONCE(needs_membase(port->iotype) && !port->membase)) + return -ENODEV; + if (WARN_ON_ONCE(needs_iobase(port->iotype) && !port->iobase)) + return -ENODEV; + if (!port->fifosize) port->fifosize = uart_config[port->type].fifo_size; if (!up->tx_loadsz) @@ -3157,6 +3189,17 @@ serial8250_verify_port(struct uart_port *port, struct serial_struct *ser) ser->type >= ARRAY_SIZE(uart_config) || ser->type == PORT_CIRRUS || ser->type == PORT_STARTECH) return -EINVAL; + + /* + * This driver clearly was intended to support switching between + * io types (see serial8250_do_startup()), so we need to ensure that + * the underlying port type will support the request. + */ + if (needs_membase(ser->io_type) && !port->membase) + return -EINVAL; + if (needs_iobase(ser->io_type) && !port->iobase) + return -EINVAL; + return 0; } -- 2.16.1.72.g5be1f00a9.dirty