[PATCH 5.4 022/389] tty: vt: initialize unicode screen buffer

Greg Kroah-Hartman
2022-08-23T11:09:11Z

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit af77c56aa35325daa2bc2bed5c2ebf169be61b86 upstream.

syzbot reports kernel infoleak at vcs_read() [1], for buffer can be read
immediately after resize operation. Initialize buffer using kzalloc().

----------
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/fb.h>

int main(int argc, char *argv[])
{
struct fb_var_screeninfo var = { };
const int fb_fd = open("/dev/fb0", 3);
ioctl(fb_fd, FBIOGET_VSCREENINFO, &var);
var.yres = 0x21;
ioctl(fb_fd, FBIOPUT_VSCREENINFO, &var);
return read(open("/dev/vcsu", O_RDONLY), &var, sizeof(var)) == -1;
}
----------

Link: https://syzkaller.appspot.com/bug?extid=31a641689d43387f05d3 [1]
Cc: stable <stable@vger.kernel.org>
Reported-by: syzbot <syzbot+31a641689d43387f05d3@syzkaller.appspotmail.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/4ef053cf-e796-fb5e-58b7-3ae58242a4ad@I-love.SAKURA.ne.jp
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/vt/vt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -351,7 +351,7 @@ static struct uni_screen *vc_uniscr_allo
/* allocate everything in one go */
memsize = cols * rows * sizeof(char32_t);
memsize += rows * sizeof(char32_t *);
- p = vmalloc(memsize);
+ p = vzalloc(memsize);
if (!p)
return NULL;