=====================================================
BUG: KMSAN: kernel-infoleak in instrument_copy_to_user include/linux/instrumented.h:114 [inline]
BUG: KMSAN: kernel-infoleak in copy_to_user_iter lib/iov_iter.c:24 [inline]
BUG: KMSAN: kernel-infoleak in iterate_ubuf include/linux/iov_iter.h:30 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
BUG: KMSAN: kernel-infoleak in iterate_and_advance include/linux/iov_iter.h:330 [inline]
BUG: KMSAN: kernel-infoleak in _copy_to_iter+0xef3/0x33f0 lib/iov_iter.c:185
 instrument_copy_to_user include/linux/instrumented.h:114 [inline]
 copy_to_user_iter lib/iov_iter.c:24 [inline]
 iterate_ubuf include/linux/iov_iter.h:30 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:302 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0xef3/0x33f0 lib/iov_iter.c:185
 copy_page_to_iter+0x482/0x910 lib/iov_iter.c:362
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 filemap_read+0x1cda/0x2300 mm/filemap.c:2799
 blkdev_read_iter+0x89f/0xb00 block/fops.c:859
 new_sync_read fs/read_write.c:491 [inline]
 vfs_read+0x8ed/0xf90 fs/read_write.c:572
 ksys_read fs/read_write.c:715 [inline]
 __do_sys_read fs/read_write.c:724 [inline]
 __se_sys_read fs/read_write.c:722 [inline]
 __x64_sys_read+0x1fb/0x4d0 fs/read_write.c:722
 x64_sys_call+0x2f9c/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:1
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was stored to memory at:
 memcpy_to_iter lib/iov_iter.c:65 [inline]
 iterate_bvec include/linux/iov_iter.h:123 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 _copy_to_iter+0x130f/0x33f0 lib/iov_iter.c:185
 copy_page_to_iter+0x482/0x910 lib/iov_iter.c:362
 copy_folio_to_iter include/linux/uio.h:204 [inline]
 shmem_file_read_iter+0x904/0x1140 mm/shmem.c:3414
 lo_rw_aio+0x1268/0x1590 drivers/block/loop.c:-1
 do_req_filebacked drivers/block/loop.c:-1 [inline]
 loop_handle_cmd drivers/block/loop.c:1923 [inline]
 loop_process_work+0xe30/0x1ec0 drivers/block/loop.c:1958
 loop_workfn+0x3e/0x60 drivers/block/loop.c:1982
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xb91/0x1d80 kernel/workqueue.c:3346
 worker_thread+0xedf/0x1590 kernel/workqueue.c:3427
 kthread+0xd5c/0xf00 kernel/kthread.c:463
 ret_from_fork+0x1f5/0x4c0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Uninit was stored to memory at:
 memcpy_from_iter lib/iov_iter.c:73 [inline]
 iterate_bvec include/linux/iov_iter.h:123 [inline]
 iterate_and_advance2 include/linux/iov_iter.h:306 [inline]
 iterate_and_advance include/linux/iov_iter.h:330 [inline]
 __copy_from_iter lib/iov_iter.c:249 [inline]
 copy_folio_from_iter_atomic+0x11f7/0x3c20 lib/iov_iter.c:479
 generic_perform_write+0x8b1/0x1050 mm/filemap.c:4272
 shmem_file_write_iter+0x2b7/0x2f0 mm/shmem.c:3466
 lo_rw_aio+0x1268/0x1590 drivers/block/loop.c:-1
 do_req_filebacked drivers/block/loop.c:-1 [inline]
 loop_handle_cmd drivers/block/loop.c:1923 [inline]
 loop_process_work+0xe30/0x1ec0 drivers/block/loop.c:1958
 loop_workfn+0x3e/0x60 drivers/block/loop.c:1982
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xb91/0x1d80 kernel/workqueue.c:3346
 worker_thread+0xedf/0x1590 kernel/workqueue.c:3427
 kthread+0xd5c/0xf00 kernel/kthread.c:463
 ret_from_fork+0x1f5/0x4c0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Uninit was created at:
 __alloc_frozen_pages_noprof+0x689/0xf00 mm/page_alloc.c:5201
 __alloc_pages_noprof mm/page_alloc.c:5212 [inline]
 alloc_pages_bulk_noprof+0x1518/0x1950 mm/page_alloc.c:5132
 btrfs_alloc_page_array fs/btrfs/extent_io.c:678 [inline]
 alloc_eb_folio_array+0x15a/0x670 fs/btrfs/extent_io.c:702
 alloc_extent_buffer+0x884/0x3ce0 fs/btrfs/extent_io.c:3423
 btrfs_find_create_tree_block+0x44/0x60 fs/btrfs/disk-io.c:606
 btrfs_init_new_buffer fs/btrfs/extent-tree.c:5062 [inline]
 btrfs_alloc_tree_block+0x3fe/0x1bc0 fs/btrfs/extent-tree.c:5175
 btrfs_alloc_log_tree_node fs/btrfs/disk-io.c:939 [inline]
 btrfs_add_log_tree+0x243/0x7a0 fs/btrfs/disk-io.c:987
 start_log_trans fs/btrfs/tree-log.c:348 [inline]
 btrfs_log_inode_parent+0x9ca/0x1e40 fs/btrfs/tree-log.c:7486
 btrfs_log_dentry_safe+0x96/0x130 fs/btrfs/tree-log.c:7592
 btrfs_sync_file+0x1991/0x22e0 fs/btrfs/file.c:1732
 vfs_fsync_range+0x1a1/0x240 fs/sync.c:187
 generic_write_sync include/linux/fs.h:3048 [inline]
 btrfs_do_write_iter+0xa8f/0xcb0 fs/btrfs/file.c:1469
 btrfs_file_write_iter+0x38/0x50 fs/btrfs/file.c:1479
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0xbe2/0x15d0 fs/read_write.c:686
 ksys_write fs/read_write.c:738 [inline]
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746
 x64_sys_call+0x3014/0x3e30 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xd9/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Bytes 3960-3967 of 4096 are uninitialized
Memory access of size 4096 starts at ffff88808ee1a000
Data copied to user address 000020000051dc40

CPU: 1 UID: 0 PID: 21002 Comm: syz.3.3501 Not tainted syzkaller #0 PREEMPT(none) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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