Re: BUG: unable to handle kernel NULL pointer dereference in mem_serial_out

Dmitry Vyukov
2019-12-18T06:54:02Z

On Wed, Dec 18, 2019 at 1:56 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> Hmm, this is a surprising bug. syzbot provided a C reproducer, but the definition
> of "struct serial_struct" used in that reproducer is wrong. As a result, syzbot was
> reporting crash caused by passing wrong arguments. ;-)

We are on it:
https://github.com/google/syzkaller/blob/master/sys/linux/dev_ptmx.txt.warn#L20-L25

> close_delay field used in the C reproducer is sizeof(unsigned int) bytes rather than
> sizeof(unsigned short) bytes, thus fields after close_delay field are incorrectly
> interpreted.
>
> ----------------------------------------
> #include <stdio.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sys/ioctl.h>
> #include <linux/serial.h>
>
> struct bad_serial_struct {
> int type;
> int line;
> unsigned int port;
> int irq;
> int flags;
> int xmit_fifo_size;
> int custom_divisor;
> int baud_base;
> unsigned int close_delay; /* Correct type is "unsigned short". */
> char io_type;
> char reserved_char[1];
> int hub6;
> unsigned short closing_wait;
> unsigned short closing_wait2;
> unsigned char *iomem_base;
> unsigned short iomem_reg_shift;
> unsigned int port_high;
> unsigned long iomap_base;
> };
>
> int main(int argc, char *argv[])
> {
> struct bad_serial_struct ss = { };
> int fd = open("/dev/ttyS3", O_RDONLY);
> ss.type = 0xa;
> ss.line = 0x400000;
> ss.port = 0x100;
> ss.irq = 0;
> ss.flags = 0x400000;
> ss.xmit_fifo_size = 0;
> ss.custom_divisor = 0;
> ss.baud_base = 0x80000;
> ss.close_delay = 0x200ff;
> ss.io_type = 0;
> ss.reserved_char[0] = 0x41;
> ss.hub6 = 3;
> ss.closing_wait = 0;
> ss.closing_wait2 = 0x7c5;
> ss.iomem_base = NULL;
> ss.iomem_reg_shift = 0;
> ss.port_high = 0;
> ss.iomap_base = 0;
> ioctl(fd, TIOCSSERIAL, &ss);
> return 0;
> }
> ----------------------------------------