euler inclusion category: bugfix bugzilla: 31340 DTS: NA CVE: CVE-2020-8649

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When syzkaller tests, there is a UAF: BUG: KASan: use after free in vgacon_invert_region+0x9d/0x110 at addr ffff880000100000 Read of size 2 by task syz-executor.1/16489 page:ffffea0000004000 count:0 mapcount:-127 mapping: (null) index:0x0 page flags: 0xfffff00000000() page dumped because: kasan: bad access detected CPU: 1 PID: 16489 Comm: syz-executor.1 Not tainted Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014 Call Trace: [<ffffffffb119f309>] dump_stack+0x1e/0x20 [<ffffffffb04af957>] kasan_report+0x577/0x950 [<ffffffffb04ae652>] __asan_load2+0x62/0x80 [<ffffffffb090f26d>] vgacon_invert_region+0x9d/0x110 [<ffffffffb0a39d95>] invert_screen+0xe5/0x470 [<ffffffffb0a21dcb>] set_selection+0x44b/0x12f0 [<ffffffffb0a3bfae>] tioclinux+0xee/0x490 [<ffffffffb0a1d114>] vt_ioctl+0xff4/0x2670 [<ffffffffb0a0089a>] tty_ioctl+0x46a/0x1a10 [<ffffffffb052db3d>] do_vfs_ioctl+0x5bd/0xc40 [<ffffffffb052e2f2>] SyS_ioctl+0x132/0x170 [<ffffffffb11c9b1b>] system_call_fastpath+0x22/0x27 Memory state around the buggy address: ffff8800000fff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff8800000fff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ffff880000100000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

It can be reproduce in the linux mainline by the program: #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/ioctl.h> #include <linux/vt.h>

struct tiocl_selection { unsigned short xs; /* X start */ unsigned short ys; /* Y start */ unsigned short xe; /* X end */ unsigned short ye; /* Y end */ unsigned short sel_mode; /* selection mode */ };

#define TIOCL_SETSEL 2 struct tiocl { unsigned char type; unsigned char pad; struct tiocl_selection sel; };

int main() { int fd = 0; const char *dev = "/dev/char/4:1";

struct vt_consize v = {0}; struct tiocl tioc = {0};

fd = open(dev, O_RDWR, 0);

v.v_rows = 3346; ioctl(fd, VT_RESIZEX, &v);

tioc.type = TIOCL_SETSEL; ioctl(fd, TIOCLINUX, &tioc);

return 0; }

When resize the screen, update the 'vc->vc_size_row' to the new_row_size, but when 'set_origin' in 'vgacon_set_origin', vgacon use 'vga_vram_base' for 'vc_origin' and 'vc_visible_origin', not 'vc_screenbuf'. It maybe smaller than 'vc_screenbuf'. When TIOCLINUX, use the new_row_size to calc the offset, it maybe larger than the vga_vram_base in vgacon driver, then bad access.

So, If the screen size larger than vga_vram, resize screen should be failed. This alse fix CVE-2020-8649

Fixes: 0aec4867dca14 ("[PATCH] SVGATextMode fix") Reported-by: Hulk Robot hulkci@huawei.com Signed-off-by: Zhang Xiaoxu zhangxiaoxu5@huawei.com --- drivers/video/console/vgacon.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c index e0de08df841b5..441e69c7e5182 100644 --- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -1270,7 +1270,10 @@ static int vgacon_font_get(struct vc_data *c, struct console_font *font) static int vgacon_resize(struct vc_data *c, unsigned int width, unsigned int height, unsigned int user) { - if (width % 2 || width > screen_info.orig_video_cols || + if (width % 2 || width * height > vga_vram_size) + return -EINVAL; + + if (width > screen_info.orig_video_cols || height > (screen_info.orig_video_lines * vga_default_font_height)/ c->vc_font.height) /* let svgatextmode tinker with video timings and