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 ==================================================================
