4.19-stable review patch. If anyone has any objections, please let me know.
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From: George Kennedy george.kennedy@oracle.com
commit 6eabce6608d6f3440f4c03aa3d3ef50a47a3d193 upstream.
Calling ioctl TIOCSSERIAL with an invalid baud_base can result in uartclk being zero, which will result in a divide by zero error in uart_get_divisor(). The check for uartclk being zero in uart_set_info() needs to be done before other settings are made as subsequent calls to ioctl TIOCSSERIAL for the same port would be impacted if the uartclk check was done where uartclk gets set.
Oops: divide error: 0000 PREEMPT SMP KASAN PTI RIP: 0010:uart_get_divisor (drivers/tty/serial/serial_core.c:580) Call Trace: <TASK> serial8250_get_divisor (drivers/tty/serial/8250/8250_port.c:2576 drivers/tty/serial/8250/8250_port.c:2589) serial8250_do_set_termios (drivers/tty/serial/8250/8250_port.c:502 drivers/tty/serial/8250/8250_port.c:2741) serial8250_set_termios (drivers/tty/serial/8250/8250_port.c:2862) uart_change_line_settings (./include/linux/spinlock.h:376 ./include/linux/serial_core.h:608 drivers/tty/serial/serial_core.c:222) uart_port_startup (drivers/tty/serial/serial_core.c:342) uart_startup (drivers/tty/serial/serial_core.c:368) uart_set_info (drivers/tty/serial/serial_core.c:1034) uart_set_info_user (drivers/tty/serial/serial_core.c:1059) tty_set_serial (drivers/tty/tty_io.c:2637) tty_ioctl (drivers/tty/tty_io.c:2647 drivers/tty/tty_io.c:2791) __x64_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:907 fs/ioctl.c:893 fs/ioctl.c:893) do_syscall_64 (arch/x86/entry/common.c:52 (discriminator 1) arch/x86/entry/common.c:83 (discriminator 1)) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
Reported-by: syzkaller syzkaller@googlegroups.com Cc: stable@vger.kernel.org Signed-off-by: George Kennedy george.kennedy@oracle.com Rule: add Link: https://lore.kernel.org/stable/1721148848-9784-1-git-send-email-george.kenne... Link: https://lore.kernel.org/r/1721219078-3209-1-git-send-email-george.kennedy@or... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/serial_core.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -857,6 +857,14 @@ static int uart_set_info(struct tty_stru new_flags = (__force upf_t)new_info->flags; old_custom_divisor = uport->custom_divisor;
+ if (!(uport->flags & UPF_FIXED_PORT)) { + unsigned int uartclk = new_info->baud_base * 16; + /* check needs to be done here before other settings made */ + if (uartclk == 0) { + retval = -EINVAL; + goto exit; + } + } if (!capable(CAP_SYS_ADMIN)) { retval = -EPERM; if (change_irq || change_port ||