| Message ID | 20240916011027.303875-1-qianqiang.liu@163.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | fbcon: Fix a NULL pointer dereference issue in fbcon_putcs | expand |
On 9/16/24 03:10, Qianqiang Liu wrote: > syzbot has found a NULL pointer dereference bug in fbcon [1]. > > This issue is caused by ops->putcs being a NULL pointer. > We need to check the pointer before using it. > > [1] https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a > > Cc: stable@vger.kernel.org > Reported-and-tested-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com > Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com> > --- > drivers/video/fbdev/core/fbcon.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c > index 3f7333dca508..96c1262cc981 100644 > --- a/drivers/video/fbdev/core/fbcon.c > +++ b/drivers/video/fbdev/core/fbcon.c > @@ -1284,7 +1284,7 @@ static void fbcon_putcs(struct vc_data *vc, const u16 *s, unsigned int count, > struct fbcon_display *p = &fb_display[vc->vc_num]; > struct fbcon_ops *ops = info->fbcon_par; > > - if (!fbcon_is_inactive(vc, info)) > + if (!fbcon_is_inactive(vc, info) && ops->putcs) I think this patch just hides the real problem. How could putcs have become NULL ? Helge > ops->putcs(vc, info, s, count, real_y(p, ypos), xpos, > get_color(vc, info, scr_readw(s), 1), > get_color(vc, info, scr_readw(s), 0));
Hi,
I simplified the C reproducer as follows:
#include <stdint.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <linux/tiocl.h>
#include <sys/ioctl.h>
struct param {
uint8_t type;
struct tiocl_selection ts;
};
int main()
{
write(1, "executing program\n", sizeof("executing program\n") - 1);
int fd = open("/dev/fb1", 0, 0);
struct fb_con2fbmap con2fb;
con2fb.console = 0x19;
con2fb.framebuffer = 0;
ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);
int fd1 = open("/dev/tty1", O_RDWR, 0);
struct param param;
param.type = 2;
param.ts.xs = 0;
param.ts.ys = 0;
param.ts.xe = 0;
param.ts.ye = 0;
param.ts.sel_mode = 0;
ioctl(fd1, TIOCLINUX, ¶m);
con2fb.console = 1;
con2fb.framebuffer = 0;
ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);
return 0;
}
But I still need time to debug the kernel code..
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 3f7333dca508..96c1262cc981 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -1284,7 +1284,7 @@ static void fbcon_putcs(struct vc_data *vc, const u16 *s, unsigned int count, struct fbcon_display *p = &fb_display[vc->vc_num]; struct fbcon_ops *ops = info->fbcon_par; - if (!fbcon_is_inactive(vc, info)) + if (!fbcon_is_inactive(vc, info) && ops->putcs) ops->putcs(vc, info, s, count, real_y(p, ypos), xpos, get_color(vc, info, scr_readw(s), 1), get_color(vc, info, scr_readw(s), 0));
syzbot has found a NULL pointer dereference bug in fbcon [1]. This issue is caused by ops->putcs being a NULL pointer. We need to check the pointer before using it. [1] https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a Cc: stable@vger.kernel.org Reported-and-tested-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com> --- drivers/video/fbdev/core/fbcon.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)