CVE-2023-52737: In the Linux kernel, the following vulnerability has been resolved:  btrfs: lock the inode in shared mode before starting fiemap  Currently fiemap does not take the inode's lock (VFS lock), it only locks a file range in the inode's io tree. This however can lead to a deadlock if we have a concurrent fsync on the file and fiemap code triggers a fault when accessing the user space buffer with fiemap_fill_next_extent(). The deadlock happens on the inode's i_mmap_lock semaphore, which is taken both by fsync and btrfs_page_mkwrite(). This deadlock was recently reported by syzbot and triggers a trace like the following:     task:syz-executor361 state:D stack:20264 pid:5668  ppid:5119   flags:0x00004004    Call Trace:     <TASK>     context_switch kernel/sched/core.c:5293 [inline]     __schedule+0x995/0xe20 kernel/sched/core.c:6606     schedule+0xcb/0x190 kernel/sched/core.c:6682     wait_on_state fs/btrfs/extent-io-tree.c:707 [inline]     wait_extent_bit+0x577/0x6f0 fs/btrfs/extent-io-tree.c:751     lock_extent+0x1c2/0x280 fs/btrfs/extent-io-tree.c:1742     find_lock_delalloc_range+0x4e6/0x9c0 fs/btrfs/extent_io.c:488     writepage_delalloc+0x1ef/0x540 fs/btrfs/extent_io.c:1863     __extent_writepage+0x736/0x14e0 fs/btrfs/extent_io.c:2174     extent_write_cache_pages+0x983/0x1220 fs/btrfs/extent_io.c:3091     extent_writepages+0x219/0x540 fs/btrfs/extent_io.c:3211     do_writepages+0x3c3/0x680 mm/page-writeback.c:2581     filemap_fdatawrite_wbc+0x11e/0x170 mm/filemap.c:388     __filemap_fdatawrite_range mm/filemap.c:421 [inline]     filemap_fdatawrite_range+0x175/0x200 mm/filemap.c:439     btrfs_fdatawrite_range fs/btrfs/file.c:3850 [inline]     start_ordered_ops fs/btrfs/file.c:1737 [inline]     btrfs_sync_file+0x4ff/0x1190 fs/btrfs/file.c:1839     generic_write_sync include/linux/fs.h:2885 [inline]     btrfs_do_write_iter+0xcd3/0x1280 fs/btrfs/file.c:1684     call_write_iter include/linux/fs.h:2189 [inline]     new_sync_write fs/read_write.c:491 [inline]     vfs_write+0x7dc/0xc50 fs/read_write.c:584     ksys_write+0x177/0x2a0 fs/read_write.c:637     do_syscall_x64 arch/x86/entry/common.c:50 [inline]     do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80     entry_SYSCALL_64_after_hwframe+0x63/0xcd    RIP: 0033:0x7f7d4054e9b9    RSP: 002b:00007f7d404fa2f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001    RAX: ffffffffffffffda RBX: 00007f7d405d87a0 RCX: 00007f7d4054e9b9    RDX: 0000000000000090 RSI: 0000000020000000 RDI: 0000000000000006    RBP: 00007f7d405a51d0 R08: 0000000000000000 R09: 0000000000000000    R10: 0000000000000000 R11: 0000000000000246 R12: 61635f65646f6e69    R13: 65646f7475616f6e R14: 7261637369646f6e R15: 00007f7d405d87a8     </TASK>    INFO: task syz-executor361:5697 blocked for more than 145 seconds.          Not tainted 6.2.0-rc3-syzkaller-00376-g7c6984405241 #0    "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.    task:syz-executor361 state:D stack:21216 pid:5697  ppid:5119   flags:0x00004004    Call Trace:     <TASK>     context_switch kernel/sched/core.c:5293 [inline]     __schedule+0x995/0xe20 kernel/sched/core.c:6606     schedule+0xcb/0x190 kernel/sched/core.c:6682     rwsem_down_read_slowpath+0x5f9/0x930 kernel/locking/rwsem.c:1095     __down_read_common+0x54/0x2a0 kernel/locking/rwsem.c:1260     btrfs_page_mkwrite+0x417/0xc80 fs/btrfs/inode.c:8526     do_page_mkwrite+0x19e/0x5e0 mm/memory.c:2947     wp_page_shared+0x15e/0x380 mm/memory.c:3295     handle_pte_fault mm/memory.c:4949 [inline]     __handle_mm_fault mm/memory.c:5073 [inline]     handle_mm_fault+0x1b79/0x26b0 mm/memory.c:5219     do_user_addr_fault+0x69b/0xcb0 arch/x86/mm/fault.c:1428     handle_page_fault arch/x86/mm/fault.c:1519 [inline]     exc_page_fault+0x7a/0x110 arch/x86/mm/fault.c:1575     asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:570    RIP: 0010:copy_user_short_string+0xd/0x40 arch/x86/lib/copy_user_64.S:233    Code: 74 0a 89 (...)    RSP: 0018:ffffc9000570f330 EFLAGS: 000502 ---truncated---