On Fri, 06 Mar 2020 21:41:13 -0800

syzbot found the following crash on:

HEAD commit: 63623fd4 Merge tag 'for-linus' of git://git.kernel.org/pub.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=11653ac3e00000 kernel config: https://syzkaller.appspot.com/x/.config?x=9833e26bab355358 dashboard link: https://syzkaller.appspot.com/bug?extid=3643a18836bce555bff6 compiler: gcc (GCC) 9.0.0 20181231 (experimental) userspace arch: i386

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com

================================================================== BUG: KASAN: use-after-free in dmabuffs_dname+0x4f4/0x560 drivers/dma-buf/dma-buf.c:48 Read of size 8 at addr ffff8880a6b390e8 by task syz-executor.1/2394

CPU: 1 PID: 2394 Comm: syz-executor.1 Not tainted 5.6.0-rc3-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:641 __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135 dmabuffs_dname+0x4f4/0x560 drivers/dma-buf/dma-buf.c:48 tomoyo_realpath_from_path+0x165/0x660 security/tomoyo/realpath.c:259 tomoyo_get_realpath security/tomoyo/file.c:151 [inline] tomoyo_check_open_permission+0x2a3/0x3e0 security/tomoyo/file.c:771 tomoyo_file_open security/tomoyo/tomoyo.c:319 [inline] tomoyo_file_open+0xa9/0xd0 security/tomoyo/tomoyo.c:314 security_file_open+0x71/0x300 security/security.c:1529 do_dentry_open+0x37a/0x1380 fs/open.c:784 vfs_open+0xa0/0xd0 fs/open.c:914 do_last fs/namei.c:3490 [inline] path_openat+0x12ee/0x3490 fs/namei.c:3607 do_filp_open+0x192/0x260 fs/namei.c:3637 do_sys_openat2+0x5eb/0x7e0 fs/open.c:1149 do_sys_open+0xf2/0x180 fs/open.c:1165 __do_compat_sys_open fs/open.c:1212 [inline] __se_compat_sys_open fs/open.c:1210 [inline] __ia32_compat_sys_open+0x79/0xb0 fs/open.c:1210 do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline] do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139 RIP: 0023:0xf7fd8e39 Code: 1d 00 00 00 89 d3 5b 5e 5d c3 8b 04 24 c3 8b 1c 24 c3 8b 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90 RSP: 002b:00000000f5db2014 EFLAGS: 00000296 ORIG_RAX: 0000000000000005 RAX: ffffffffffffffda RBX: 00000000f5db204c RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000c09 RDI: 00000000f5db204c RBP: 00000000f5db2168 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 2388: save_stack+0x23/0x90 mm/kasan/common.c:72 set_track mm/kasan/common.c:80 [inline] __kasan_kmalloc mm/kasan/common.c:515 [inline] __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:488 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529 __do_kmalloc mm/slab.c:3656 [inline] __kmalloc+0x163/0x770 mm/slab.c:3665 kmalloc include/linux/slab.h:560 [inline] kzalloc include/linux/slab.h:669 [inline] dma_buf_export+0x24d/0xa80 drivers/dma-buf/dma-buf.c:533 ion_alloc drivers/staging/android/ion/ion.c:386 [inline] ion_ioctl+0x5a9/0xd20 drivers/staging/android/ion/ion.c:495 compat_ptr_ioctl+0x6e/0xa0 fs/ioctl.c:804 __do_compat_sys_ioctl fs/ioctl.c:857 [inline] __se_compat_sys_ioctl fs/ioctl.c:808 [inline] __ia32_compat_sys_ioctl+0x245/0x2c0 fs/ioctl.c:808 do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline] do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Freed by task 2380: 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:337 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/common.c:476 kasan_slab_free+0xe/0x10 mm/kasan/common.c:485 __cache_free mm/slab.c:3426 [inline] kfree+0x10a/0x2c0 mm/slab.c:3757 dma_buf_release+0x343/0x420 drivers/dma-buf/dma-buf.c:111 __fput+0x2ff/0x890 fs/file_table.c:280 ____fput+0x16/0x20 fs/file_table.c:313 task_work_run+0x145/0x1c0 kernel/task_work.c:113 tracehook_notify_resume include/linux/tracehook.h:188 [inline] exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline] syscall_return_slowpath arch/x86/entry/common.c:278 [inline] do_syscall_32_irqs_on arch/x86/entry/common.c:352 [inline] do_fast_syscall_32+0xbbd/0xe16 arch/x86/entry/common.c:408 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

The buggy address belongs to the object at ffff8880a6b39000 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 232 bytes inside of 1024-byte region [ffff8880a6b39000, ffff8880a6b39400) The buggy address belongs to the page: page:ffffea00029ace40 refcount:1 mapcount:0 mapping:ffff8880aa400c40 index:0x0 flags: 0xfffe0000000200(slab) raw: 00fffe0000000200 ffffea0002346b48 ffffea00022f49c8 ffff8880aa400c40 raw: 0000000000000000 ffff8880a6b39000 0000000100000002 0000000000000000 page dumped because: kasan: bad access detected

Memory state around the buggy address: ffff8880a6b38f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff8880a6b39000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

...

ffff8880a6b39080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

                                                      ^

ffff8880a6b39100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff8880a6b39180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================

Add a completion for dmabuf releaser to wait those who are either holding the resv lock or aquiring it.

--- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -334,6 +334,9 @@ struct dma_buf {

__poll_t active; } cb_excl, cb_shared; + + atomic_t resv_user; + struct completion done; };

/** --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -45,11 +45,20 @@ static char *dmabuffs_dname(struct dentr size_t ret = 0;

dmabuf = dentry->d_fsdata; + if (!dmabuf) + goto print_name; + + atomic_inc(&dmabuf->resv_user); + dma_resv_lock(dmabuf->resv, NULL); if (dmabuf->name) ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN); dma_resv_unlock(dmabuf->resv);

+ if (atomic_dec_and_test(&dmabuf->resv_user)) + complete(&dmabuf->done); + +print_name: return dynamic_dname(dentry, buffer, buflen, "/%s:%s", dentry->d_name.name, ret > 0 ? name : ""); } @@ -85,6 +94,10 @@ static int dma_buf_release(struct inode return -EINVAL;

dmabuf = file->private_data; + file->f_path.dentry->d_fsdata = NULL; + atomic_inc(&dmabuf->resv_user); + if (!atomic_dec_and_test(&dmabuf->resv_user)) + wait_for_completion(&dmabuf->done);

BUG_ON(dmabuf->vmapping_counter);

@@ -562,6 +575,7 @@ struct dma_buf *dma_buf_export(const str

mutex_init(&dmabuf->lock); INIT_LIST_HEAD(&dmabuf->attachments); + init_completion(&dmabuf->done);

mutex_lock(&db_list.lock); list_add(&dmabuf->list_node, &db_list.head);