| Message ID | ZvOfwLvWdNHiU4g8@thinkpad (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | [v3] fbcon: Fix a NULL pointer dereference issue in fbcon_putcs | expand |
On 9/25/24 07:29, Qianqiang Liu wrote: > syzbot has found a NULL pointer dereference bug in fbcon. > Here is the simplified C reproducer: > > struct param { > uint8_t type; > struct tiocl_selection ts; > }; > > int main() > { > struct fb_con2fbmap con2fb; > struct param param; > > int fd = open("/dev/fb1", 0, 0); > > con2fb.console = 0x19; > con2fb.framebuffer = 0; > ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb); > > param.type = 2; > param.ts.xs = 0; param.ts.ys = 0; > param.ts.xe = 0; param.ts.ye = 0; > param.ts.sel_mode = 0; > > int fd1 = open("/dev/tty1", O_RDWR, 0); > ioctl(fd1, TIOCLINUX, ¶m); > > con2fb.console = 1; > con2fb.framebuffer = 0; > ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb); > > return 0; > } > > After calling ioctl(fd1, TIOCLINUX, ¶m), the subsequent ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb) > causes the kernel to follow a different execution path: > > set_con2fb_map > -> con2fb_init_display > -> fbcon_set_disp > -> redraw_screen > -> hide_cursor > -> clear_selection > -> highlight > -> invert_screen > -> do_update_region > -> fbcon_putcs > -> ops->putcs > > Since ops->putcs is a NULL pointer, this leads to a kernel panic. > To prevent this, we need to call set_blitting_type() within set_con2fb_map() > to properly initialize ops->putcs. > > Reported-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a > Tested-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com > Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com> > --- > Changes since v2: > - Document the commit message in more detail Queued up in for-next branch of fbdev git tree. Thanks! Helge > --- > Changes since v1: > - Initialize ops->putcs by calling set_blitting_type() > --- > drivers/video/fbdev/core/fbcon.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c > index 2e093535884b..d9abae2516d8 100644 > --- a/drivers/video/fbdev/core/fbcon.c > +++ b/drivers/video/fbdev/core/fbcon.c > @@ -861,6 +861,8 @@ static int set_con2fb_map(int unit, int newidx, int user) > return err; > > fbcon_add_cursor_work(info); > + } else if (vc) { > + set_blitting_type(vc, info); > } > > con2fb_map[unit] = newidx;
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 2e093535884b..d9abae2516d8 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -861,6 +861,8 @@ static int set_con2fb_map(int unit, int newidx, int user) return err; fbcon_add_cursor_work(info); + } else if (vc) { + set_blitting_type(vc, info); } con2fb_map[unit] = newidx;
syzbot has found a NULL pointer dereference bug in fbcon. Here is the simplified C reproducer: struct param { uint8_t type; struct tiocl_selection ts; }; int main() { struct fb_con2fbmap con2fb; struct param param; int fd = open("/dev/fb1", 0, 0); con2fb.console = 0x19; con2fb.framebuffer = 0; ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb); param.type = 2; param.ts.xs = 0; param.ts.ys = 0; param.ts.xe = 0; param.ts.ye = 0; param.ts.sel_mode = 0; int fd1 = open("/dev/tty1", O_RDWR, 0); ioctl(fd1, TIOCLINUX, ¶m); con2fb.console = 1; con2fb.framebuffer = 0; ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb); return 0; } After calling ioctl(fd1, TIOCLINUX, ¶m), the subsequent ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb) causes the kernel to follow a different execution path: set_con2fb_map -> con2fb_init_display -> fbcon_set_disp -> redraw_screen -> hide_cursor -> clear_selection -> highlight -> invert_screen -> do_update_region -> fbcon_putcs -> ops->putcs Since ops->putcs is a NULL pointer, this leads to a kernel panic. To prevent this, we need to call set_blitting_type() within set_con2fb_map() to properly initialize ops->putcs. Reported-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3d613ae53c031502687a Tested-by: syzbot+3d613ae53c031502687a@syzkaller.appspotmail.com Signed-off-by: Qianqiang Liu <qianqiang.liu@163.com> --- Changes since v2: - Document the commit message in more detail --- Changes since v1: - Initialize ops->putcs by calling set_blitting_type() --- drivers/video/fbdev/core/fbcon.c | 2 ++ 1 file changed, 2 insertions(+)