On Tue, Jun 02, 2020 at 04:35:33PM -0400, Kyungtae Kim wrote: > We report a bug (in linux-5.6.11) found by FuzzUSB (a modified version > of syzkaller) > > This bug happened when accessing a deallocated instance in printer_read(). > > printer_read() tries to access lock_printer_io of the printer_dev instance > (f_printer.c:430). However, UAF arises because it had been freed > by gprinter_free(). > > To fix, we can check if an instance of printer_dev is still in use > before deallocating it. > > kernel config: https://kt0755.github.io/etc/config_v5.6.11 > > ================================================================== > BUG: KASAN: use-after-free in __mutex_lock_common > kernel/locking/mutex.c:938 [inline] > BUG: KASAN: use-after-free in __mutex_lock+0x13a7/0x14d0 > kernel/locking/mutex.c:1103 > Read of size 8 at addr ffff8880540c3890 by task syz-executor.0/6819 > > CPU: 1 PID: 6819 Comm: syz-executor.0 Not tainted 5.6.11 #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0xce/0x128 lib/dump_stack.c:118 > print_address_description.constprop.4+0x21/0x3c0 mm/kasan/report.c:374 > __kasan_report+0x131/0x1b0 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 > __mutex_lock_common kernel/locking/mutex.c:938 [inline] > __mutex_lock+0x13a7/0x14d0 kernel/locking/mutex.c:1103 > mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1118 > printer_read+0xbc/0xd60 drivers/usb/gadget/function/f_printer.c:430 > __vfs_read+0x85/0x110 fs/read_write.c:425 > vfs_read+0x161/0x380 fs/read_write.c:461 > ksys_read+0x18a/0x220 fs/read_write.c:587 > __do_sys_read fs/read_write.c:597 [inline] > __se_sys_read fs/read_write.c:595 [inline] > __x64_sys_read+0x73/0xb0 fs/read_write.c:595 > do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x4531a9 > Code: ed 60 fc 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 bb 60 fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007f0024694c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 > RAX: ffffffffffffffda RBX: 000000000073bfa8 RCX: 00000000004531a9 > RDX: 000000000000006b RSI: 0000000020000100 RDI: 0000000000000003 > RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004bd843 > R13: 00000000004d3468 R14: 00007f00246956d4 R15: 00000000ffffffff > > Allocated by task 2420: > save_stack+0x21/0x90 mm/kasan/common.c:72 > set_track mm/kasan/common.c:80 [inline] > __kasan_kmalloc.constprop.3+0xa7/0xd0 mm/kasan/common.c:515 > kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529 > kmem_cache_alloc_trace+0xfa/0x2d0 mm/slub.c:2813 > kmalloc include/linux/slab.h:555 [inline] > kzalloc include/linux/slab.h:669 [inline] > gprinter_alloc+0xa1/0x870 drivers/usb/gadget/function/f_printer.c:1416 > usb_get_function+0x58/0xc0 drivers/usb/gadget/functions.c:61 > config_usb_cfg_link+0x1ed/0x3e0 drivers/usb/gadget/configfs.c:444 > configfs_symlink+0x527/0x11d0 fs/configfs/symlink.c:202 > vfs_symlink+0x33d/0x5b0 fs/namei.c:4201 > do_symlinkat+0x11b/0x1d0 fs/namei.c:4228 > __do_sys_symlinkat fs/namei.c:4242 [inline] > __se_sys_symlinkat fs/namei.c:4239 [inline] > __x64_sys_symlinkat+0x73/0xb0 fs/namei.c:4239 > do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Freed by task 6798: > save_stack+0x21/0x90 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+0x135/0x190 mm/kasan/common.c:476 > kasan_slab_free+0xe/0x10 mm/kasan/common.c:485 > slab_free_hook mm/slub.c:1444 [inline] > slab_free_freelist_hook mm/slub.c:1477 [inline] > slab_free mm/slub.c:3034 [inline] > kfree+0xf7/0x410 mm/slub.c:3995 > gprinter_free+0x49/0xd0 drivers/usb/gadget/function/f_printer.c:1353 > usb_put_function+0x38/0x50 drivers/usb/gadget/functions.c:87 > config_usb_cfg_unlink+0x2db/0x3b0 drivers/usb/gadget/configfs.c:485 > configfs_unlink+0x3b9/0x7f0 fs/configfs/symlink.c:250 > vfs_unlink+0x287/0x570 fs/namei.c:4073 > do_unlinkat+0x4f9/0x620 fs/namei.c:4137 > __do_sys_unlink fs/namei.c:4184 [inline] > __se_sys_unlink fs/namei.c:4182 [inline] > __x64_sys_unlink+0x42/0x50 fs/namei.c:4182 > do_syscall_64+0x9e/0x510 arch/x86/entry/common.c:294 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > The buggy address belongs to the object at ffff8880540c3800 > which belongs to the cache kmalloc-1k of size 1024 > The buggy address is located 144 bytes inside of > 1024-byte region [ffff8880540c3800, ffff8880540c3c00) > The buggy address belongs to the page: > page:ffffea0001503000 refcount:1 mapcount:0 mapping:ffff88806c00e300 > index:0xffff8880540c4800 compound_mapcount: 0 > flags: 0x100000000010200(slab|head) > raw: 0100000000010200 ffffea0001ae3808 ffffea0001ac6c08 ffff88806c00e300 > raw: ffff8880540c4800 0000000000100007 00000001ffffffff 0000000000000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff8880540c3780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > ffff8880540c3800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > >ffff8880540c3880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ^ > ffff8880540c3900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff8880540c3980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ================================================================== Can you send a patch to fix this so that you get full credit for finding, and fixing the issue? thanks, greg k-h
