In hugetlb_handle_userfault, we call i_mmap_unlock_read before handle_userfault,
and call i_mmap_lock_read after it to make calling code simpler.
But the mapping variable can be invalid as vma may be changed
after mmap lock is dropped during handle_userfault.
This bug is found by syzkaller with the following operations:
mmap$IORING_OFF_SQ_RING(&(0x7f0000400000/0xc00000)=nil, 0xc00000, 0x0, 0x44832, 0xffffffffffffffff, 0x0)
r0 = userfaultfd(0x0)
r1 = openat(0xffffffffffffff9c, &(0x7f00000000c0)='./file2\x00', 0x59042, 0x0)
ftruncate(r1, 0x8)
r2 = mmap$IORING_OFF_SQ_RING(&(0x7f0000400000/0xc00000)=nil, 0xc00000, 0x2000002, 0x44832, r1, 0x0)
syz_memcpy_off$IO_URING_METADATA_FLAGS(r2, 0x0, &(0x7f0000000080), 0x0, 0x4)
syz_memcpy_off$IO_URING_METADATA_FLAGS(r2, 0x118, &(0x7f0000000280)=0x1, 0x0, 0x4)
ioctl$UFFDIO_API(r0, 0xc018aa3f, &(0x7f0000000180))
mprotect(&(0x7f0000ffb000/0x2000)=nil, 0x2000, 0x0)
ioctl$UFFDIO_REGISTER(r0, 0xc020aa00, &(0x7f0000000080)={{&(0x7f0000800000/0x800000)=nil, 0x800000}, 0x1})
mprotect(&(0x7f0000971000/0x3000)=nil, 0x3000, 0x0)
ioctl$UFFDIO_ZEROPAGE(r0, 0xc020aa04, &(0x7f0000000000)={{&(0x7f0000b35000/0x1000)=nil, 0x1000}})
r3 = fsmount(0xffffffffffffffff, 0x1, 0x0)
syz_kvm_setup_cpu$arm64(0xffffffffffffffff, r3, &(0x7f0000dbc000/0x18000)=nil, &(0x7f00000000c0)=[{0x0, &(0x7f0000000040)="17eb9261c249c6672ae95a46cbb140cbc2b0a3b8778ee972d27c7edcf4af5d7071ceebe27cda5f06301fa270d201883b9244", 0x32}], 0x1, 0x0, &(0x7f0000000100), 0x1)
r4 = openat(0xffffffffffffff9c, &(0x7f00000000c0)='./file2\x00', 0x59042, 0x0)
ftruncate(r4, 0x8)
mmap$IORING_OFF_SQ_RING(&(0x7f0000400000/0xc00000)=nil, 0xc00000, 0x2000002, 0x44832, r4, 0x0)
KASAN report is here:
[ 476.621494] ==================================================================
[ 476.622067] BUG: KASAN: use-after-free in down_read+0x80/0x1d0
[ 476.622530] Write of size 8 at addr ffff0000cce177e0 by task syz-executor/15650
[ 476.623305] CPU: 3 PID: 15650 Comm: syz-executor Kdump: loaded Not tainted 6.0.0-rc5+ #4
[ 476.624130] Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
[ 476.624834] Call trace:
[ 476.625135] dump_backtrace+0xe4/0x124
[ 476.625586] show_stack+0x20/0x5c
[ 476.625983] dump_stack_lvl+0x68/0x84
[ 476.626415] print_address_description.constprop.0+0x78/0x360
[ 476.627046] print_report+0x108/0x130
[ 476.627473] kasan_report+0x84/0x120
[ 476.627892] kasan_check_range+0xe4/0x190
[ 476.628351] __kasan_check_write+0x28/0x3c
[ 476.628818] down_read+0x80/0x1d0
[ 476.629210] hugetlb_handle_userfault+0x120/0x1a0
[ 476.629748] hugetlb_no_page+0x618/0x6a0
[ 476.630202] hugetlb_fault+0x1d4/0x5f4
[ 476.630642] handle_mm_fault+0x23c/0x2d0
[ 476.631102] do_page_fault+0x1c0/0x5b0
[ 476.631542] do_translation_fault+0x8c/0xc0
[ 476.632022] do_mem_abort+0x68/0xfc
[ 476.632444] el0_da+0x40/0xd0
[ 476.632810] el0t_64_sync_handler+0x68/0xc0
[ 476.633292] el0t_64_sync+0x180/0x184
[ 476.633953] Allocated by task 15650:
[ 476.634368] kasan_save_stack+0x2c/0x54
[ 476.634819] __kasan_slab_alloc+0x6c/0x90
[ 476.635285] kmem_cache_alloc_lru+0x100/0x290
[ 476.635784] hugetlbfs_alloc_inode+0xac/0x2a0
[ 476.636287] alloc_inode+0x44/0x124
[ 476.636706] new_inode+0x7c/0x170
[ 476.637105] hugetlbfs_get_inode+0x158/0x2a0
[ 476.637601] hugetlb_file_setup+0xcc/0x49c
[ 476.638073] ksys_mmap_pgoff+0xe8/0x270
[ 476.638521] __arm64_sys_mmap+0x8c/0xb0
[ 476.638970] invoke_syscall+0x68/0x1a0
[ 476.639412] el0_svc_common.constprop.0+0x1e4/0x220
[ 476.639962] do_el0_svc+0x3c/0x50
[ 476.640358] el0_svc+0x28/0xd0
[ 476.640731] el0t_64_sync_handler+0xb8/0xc0
[ 476.641214] el0t_64_sync+0x180/0x184
[ 476.641868] Freed by task 0:
[ 476.642222] kasan_save_stack+0x2c/0x54
[ 476.642673] kasan_set_track+0x2c/0x40
[ 476.643114] kasan_set_free_info+0x28/0x50
[ 476.643586] ____kasan_slab_free+0x140/0x1d0
[ 476.644076] __kasan_slab_free+0x18/0x2c
[ 476.644533] kmem_cache_free+0x178/0x3f0
[ 476.644990] hugetlbfs_free_inode+0x24/0x30
[ 476.645472] i_callback+0x34/0x64
[ 476.645874] rcu_do_batch+0x240/0x660
[ 476.646307] rcu_core+0x1ec/0x270
[ 476.646708] rcu_core_si+0x18/0x24
[ 476.647115] __do_softirq+0x19c/0x540
[ 476.647765] Last potentially related work creation:
[ 476.648313] kasan_save_stack+0x2c/0x54
[ 476.648759] __kasan_record_aux_stack+0xa0/0xd0
[ 476.649276] kasan_record_aux_stack_noalloc+0x14/0x20
[ 476.649858] call_rcu+0xbc/0x370
[ 476.650249] destroy_inode+0x9c/0xc4
[ 476.650674] evict+0x2cc/0x3a0
[ 476.651048] iput_final+0x144/0x314
[ 476.651463] iput.part.0+0x114/0x130
[ 476.651887] iput+0x38/0x50
[ 476.652235] dentry_unlink_inode+0x150/0x210
[ 476.652729] __dentry_kill+0x1f8/0x3a0
[ 476.653168] dentry_kill+0x390/0x500
[ 476.653601] dput+0x304/0x354
[ 476.653967] __fput+0x138/0x360
[ 476.654352] ____fput+0x18/0x24
[ 476.654736] task_work_run+0x17c/0x340
[ 476.655181] ptrace_notify+0x1d0/0x1e0
[ 476.655625] syscall_trace_exit+0x1e4/0x320
[ 476.656107] el0_svc_common.constprop.0+0xc8/0x220
[ 476.656649] do_el0_svc+0x3c/0x50
[ 476.657047] el0_svc+0x28/0xd0
[ 476.657423] el0t_64_sync_handler+0xb8/0xc0
[ 476.657918] el0t_64_sync+0x180/0x184
[ 476.658567] Second to last potentially related work creation:
[ 476.659196] kasan_save_stack+0x2c/0x54
[ 476.659644] __kasan_record_aux_stack+0xa0/0xd0
[ 476.660162] kasan_record_aux_stack_noalloc+0x14/0x20
[ 476.660728] call_rcu+0xbc/0x370
[ 476.661117] destroy_inode+0x9c/0xc4
[ 476.661544] evict+0x2cc/0x3a0
[ 476.661917] iput_final+0x144/0x314
[ 476.662334] iput.part.0+0x114/0x130
[ 476.662759] iput+0x38/0x50
[ 476.663107] dentry_unlink_inode+0x150/0x210
[ 476.663599] __dentry_kill+0x1f8/0x3a0
[ 476.664039] dentry_kill+0x390/0x500
[ 476.664463] dput+0x304/0x354
[ 476.664828] __fput+0x138/0x360
[ 476.665211] ____fput+0x18/0x24
[ 476.665600] task_work_run+0x17c/0x340
[ 476.666041] do_notify_resume+0x230/0x320
[ 476.666509] el0_svc+0x8c/0xd0
[ 476.666883] el0t_64_sync_handler+0xb8/0xc0
[ 476.667367] el0t_64_sync+0x180/0x184
[ 476.668016] The buggy address belongs to the object at ffff0000cce17600
which belongs to the cache hugetlbfs_inode_cache of size 640
[ 476.669451] The buggy address is located 480 bytes inside of
640-byte region [ffff0000cce17600, ffff0000cce17880)
[ 476.670958] The buggy address belongs to the physical page:
[ 476.671575] page:0000000032d18387 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff0000cce14600 pfn:0x10ce14
[ 476.672686] head:0000000032d18387 order:2 compound_mapcount:0 compound_pincount:0
[ 476.673486] memcg:ffff0000c500ec01
[ 476.673893] flags: 0x17ffff800010200(slab|head|node=0|zone=2|lastcpupid=0xfffff)
[ 476.674692] raw: 017ffff800010200 fffffc00005f1300 dead000000000002 ffff0000c15b5680
[ 476.675517] raw: ffff0000cce14600 000000008015000f 00000001ffffffff ffff0000c500ec01
[ 476.676339] page dumped because: kasan: bad access detected
[ 476.677170] Memory state around the buggy address:
[ 476.677715] ffff0000cce17680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 476.678489] ffff0000cce17700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 476.679265] >ffff0000cce17780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 476.680034] ^
[ 476.680725] ffff0000cce17800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 476.681498] ffff0000cce17880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
[ 476.682271] ==================================================================
