Subject: KASAN: use-after-free Read in vgem_gem_dumb_create

From: syzbot <[email-masked]>
Date: Fri, 31 Jan 2020 14:28:10 -0800

Hello,

syzbot found the following crash on:

HEAD commit:    39bed42d Merge tag 'for-linus-hmm' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=179465bee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2646535f8818ae25
dashboard link: https://syzkaller.appspot.com/bug?extid=0dc4444774d419e916c8
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16251279e00000

The bug was bisected to:

commit 7611750784664db46d0db95631e322aeb263dde7
Author: Alex Deucher <[email-masked]>
Date:   Wed Jun 21 16:31:41 2017 +0000

    drm/amdgpu: use kernel is_power_of_2 rather than local version

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11628df1e00000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=13628df1e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=15628df1e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email-masked]
Fixes: 761175078466 ("drm/amdgpu: use kernel is_power_of_2 rather than local version")

==================================================================
BUG: KASAN: use-after-free in vgem_gem_dumb_create+0x238/0x250 drivers/gpu/drm/vgem/vgem_drv.c:221
Read of size 8 at addr ffff88809fa67908 by task syz-executor.0/14871

CPU: 0 PID: 14871 Comm: syz-executor.0 Not tainted 5.5.0-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+0x197/0x210 lib/dump_stack.c:118
 print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
 __kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
 kasan_report+0x12/0x20 mm/kasan/common.c:639
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
 vgem_gem_dumb_create+0x238/0x250 drivers/gpu/drm/vgem/vgem_drv.c:221
 drm_mode_create_dumb+0x282/0x310 drivers/gpu/drm/drm_dumb_buffers.c:94
 drm_mode_create_dumb_ioctl+0x26/0x30 drivers/gpu/drm/drm_dumb_buffers.c:100
 drm_ioctl_kernel+0x244/0x300 drivers/gpu/drm/drm_ioctl.c:786
 drm_ioctl+0x54e/0xa60 drivers/gpu/drm/drm_ioctl.c:886
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45b349
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f871af46c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f871af476d4 RCX: 000000000045b349
RDX: 0000000020000180 RSI: 00000000c02064b2 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000285 R14: 00000000004d14d0 R15: 000000000075bf2c

Allocated by task 14871:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 __kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
 kmem_cache_alloc_trace+0x158/0x790 mm/slab.c:3551
 kmalloc include/linux/slab.h:556 [inline]
 kzalloc include/linux/slab.h:670 [inline]
 __vgem_gem_create+0x49/0x100 drivers/gpu/drm/vgem/vgem_drv.c:165
 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:194 [inline]
 vgem_gem_dumb_create+0xd7/0x250 drivers/gpu/drm/vgem/vgem_drv.c:217
 drm_mode_create_dumb+0x282/0x310 drivers/gpu/drm/drm_dumb_buffers.c:94
 drm_mode_create_dumb_ioctl+0x26/0x30 drivers/gpu/drm/drm_dumb_buffers.c:100
 drm_ioctl_kernel+0x244/0x300 drivers/gpu/drm/drm_ioctl.c:786
 drm_ioctl+0x54e/0xa60 drivers/gpu/drm/drm_ioctl.c:886
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 14871:
 save_stack+0x23/0x90 mm/kasan/common.c:72
 set_track mm/kasan/common.c:80 [inline]
 kasan_set_free_info mm/kasan/common.c:335 [inline]
 __kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
 kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
 __cache_free mm/slab.c:3426 [inline]
 kfree+0x10a/0x2c0 mm/slab.c:3757
 vgem_gem_free_object+0xbe/0xe0 drivers/gpu/drm/vgem/vgem_drv.c:68
 drm_gem_object_free+0x100/0x220 drivers/gpu/drm/drm_gem.c:983
 kref_put include/linux/kref.h:65 [inline]
 drm_gem_object_put_unlocked drivers/gpu/drm/drm_gem.c:1017 [inline]
 drm_gem_object_put_unlocked+0x196/0x1c0 drivers/gpu/drm/drm_gem.c:1002
 vgem_gem_create drivers/gpu/drm/vgem/vgem_drv.c:199 [inline]
 vgem_gem_dumb_create+0x115/0x250 drivers/gpu/drm/vgem/vgem_drv.c:217
 drm_mode_create_dumb+0x282/0x310 drivers/gpu/drm/drm_dumb_buffers.c:94
 drm_mode_create_dumb_ioctl+0x26/0x30 drivers/gpu/drm/drm_dumb_buffers.c:100
 drm_ioctl_kernel+0x244/0x300 drivers/gpu/drm/drm_ioctl.c:786
 drm_ioctl+0x54e/0xa60 drivers/gpu/drm/drm_ioctl.c:886
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88809fa67800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 264 bytes inside of
 1024-byte region [ffff88809fa67800, ffff88809fa67c00)
The buggy address belongs to the page:
page:ffffea00027e99c0 refcount:1 mapcount:0 mapping:ffff8880aa400c40 index:0x0
raw: 00fffe0000000200 ffffea0002293548 ffffea00023e1f08 ffff8880aa400c40
raw: 0000000000000000 ffff88809fa67000 0000000100000002 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809fa67800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809fa67880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809fa67900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88809fa67980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809fa67a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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