[PATCH AUTOSEL 6.6 56/58] fbcon: Fix a NULL pointer dereference issue in fbcon_putcs

[PATCH AUTOSEL 6.6 56/58] fbcon: Fix a NULL pointer dereference issue in fbcon_putcs

[Sasha Levin]

From: Qianqiang Liu <qianqiang.liu@163.com>

[ Upstream commit 5b97eebcce1b4f3f07a71f635d6aa3af96c236e7 ]

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, &param);

	con2fb.console = 1;
	con2fb.framebuffer = 0;
	ioctl(fd, FBIOPUT_CON2FBMAP, &con2fb);

	return 0;
}

After calling ioctl(fd1, TIOCLINUX, &param), 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>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 24035b4f2cd70..405d587450ef8 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -847,6 +847,8 @@ 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;
-- 
2.43.0

[PATCH AUTOSEL 6.6 58/58] fbdev: sisfb: Fix strbuf array overflow

[Sasha Levin]

From: Andrey Shumilin <shum.sdl@nppct.ru>

[ Upstream commit 9cf14f5a2746c19455ce9cb44341b5527b5e19c3 ]

The values of the variables xres and yres are placed in strbuf.
These variables are obtained from strbuf1.
The strbuf1 array contains digit characters
and a space if the array contains non-digit characters.
Then, when executing sprintf(strbuf, "%ux%ux8", xres, yres);
more than 16 bytes will be written to strbuf.
It is suggested to increase the size of the strbuf array to 24.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Signed-off-by: Andrey Shumilin <shum.sdl@nppct.ru>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/video/fbdev/sis/sis_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/sis/sis_main.c b/drivers/video/fbdev/sis/sis_main.c
index 6d524a65af181..ad39571f91349 100644
--- a/drivers/video/fbdev/sis/sis_main.c
+++ b/drivers/video/fbdev/sis/sis_main.c
@@ -184,7 +184,7 @@ static void sisfb_search_mode(char *name, bool quiet)
 {
 	unsigned int j = 0, xres = 0, yres = 0, depth = 0, rate = 0;
 	int i = 0;
-	char strbuf[16], strbuf1[20];
+	char strbuf[24], strbuf1[20];
 	char *nameptr = name;
 
 	/* We don't know the hardware specs yet and there is no ivideo */
-- 
2.43.0