linux-kernel - KMSAN: uninit-value in soft

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Date:   Wed, 19 Aug 2020 21:56:14 -0700
From:   syzbot <syzbot+2741e4d93bff16ad8d4d@...kaller.appspotmail.com>
To:     b.zolnierkie@...sung.com, dri-devel@...ts.freedesktop.org,
        glider@...gle.com, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: KMSAN: uninit-value in soft_cursor

Hello,

syzbot found the following issue on:

HEAD commit:    ce8056d1 wip: changed copy_from_user where instrumented
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=14dcd116900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3afe005fb99591f
dashboard link: https://syzkaller.appspot.com/bug?extid=2741e4d93bff16ad8d4d
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=103f7891900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2741e4d93bff16ad8d4d@...kaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in soft_cursor+0xa89/0x13f0 drivers/video/fbdev/core/softcursor.c:61
CPU: 0 PID: 12272 Comm: syz-executor.2 Not tainted 5.8.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x21c/0x280 lib/dump_stack.c:118
 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
 __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
 soft_cursor+0xa89/0x13f0 drivers/video/fbdev/core/softcursor.c:61
 bit_cursor+0x38c6/0x3a40 drivers/video/fbdev/core/bitblit.c:386
 fbcon_cursor+0x195e/0x1a60 drivers/video/fbdev/core/fbcon.c:1411
 set_cursor drivers/tty/vt/vt.c:915 [inline]
 redraw_screen+0x28ee/0x2980 drivers/tty/vt/vt.c:1031
 vc_do_resize+0x36a8/0x38f0 drivers/tty/vt/vt.c:1314
 vc_resize+0xc3/0xe0 drivers/tty/vt/vt.c:1334
 fbcon_modechanged+0xdc1/0x1320 drivers/video/fbdev/core/fbcon.c:2990
 fbcon_update_vcs+0x86/0xa0 drivers/video/fbdev/core/fbcon.c:3048
 fb_set_var+0x1420/0x1850 drivers/video/fbdev/core/fbmem.c:1056
 do_fb_ioctl+0xc00/0x1150 drivers/video/fbdev/core/fbmem.c:1109
 fb_ioctl+0x1e4/0x210 drivers/video/fbdev/core/fbmem.c:1185
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl fs/ioctl.c:753 [inline]
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl+0x319/0x4d0 fs/ioctl.c:760
 __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:760
 do_syscall_64+0xad/0x160 arch/x86/entry/common.c:386
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d239
Code: Bad RIP value.
RSP: 002b:00007ff9aafacc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000000d580 RCX: 000000000045d239
RDX: 0000000020000000 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 000000000118cf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 000000000169fb6f R14: 00007ff9aafad9c0 R15: 000000000118cf4c

Uninit was stored to memory at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
 kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
 kmsan_memcpy_memmove_metadata+0x272/0x2e0 mm/kmsan/kmsan.c:247
 kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:267
 __msan_memcpy+0x43/0x50 mm/kmsan/kmsan_instr.c:116
 soft_cursor+0x44d/0x13f0 drivers/video/fbdev/core/softcursor.c:50
 bit_cursor+0x38c6/0x3a40 drivers/video/fbdev/core/bitblit.c:386
 fbcon_cursor+0x195e/0x1a60 drivers/video/fbdev/core/fbcon.c:1411
 set_cursor drivers/tty/vt/vt.c:915 [inline]
 redraw_screen+0x28ee/0x2980 drivers/tty/vt/vt.c:1031
 vc_do_resize+0x36a8/0x38f0 drivers/tty/vt/vt.c:1314
 vc_resize+0xc3/0xe0 drivers/tty/vt/vt.c:1334
 fbcon_modechanged+0xdc1/0x1320 drivers/video/fbdev/core/fbcon.c:2990
 fbcon_update_vcs+0x86/0xa0 drivers/video/fbdev/core/fbcon.c:3048
 fb_set_var+0x1420/0x1850 drivers/video/fbdev/core/fbmem.c:1056
 do_fb_ioctl+0xc00/0x1150 drivers/video/fbdev/core/fbmem.c:1109
 fb_ioctl+0x1e4/0x210 drivers/video/fbdev/core/fbmem.c:1185
 vfs_ioctl fs/ioctl.c:48 [inline]
 ksys_ioctl fs/ioctl.c:753 [inline]
 __do_sys_ioctl fs/ioctl.c:762 [inline]
 __se_sys_ioctl+0x319/0x4d0 fs/ioctl.c:760
 __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:760
 do_syscall_64+0xad/0x160 arch/x86/entry/common.c:386
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Local variable ----cursor@..._cursor created at:
 bit_cursor+0xe3/0x3a40 drivers/video/fbdev/core/bitblit.c:239
 bit_cursor+0xe3/0x3a40 drivers/video/fbdev/core/bitblit.c:239
=====================================================


---
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