CVE-2024-49869: In the Linux kernel, the following vulnerability has been resolved:  btrfs: send: fix buffer overflow detection when copying path to cache entry  Starting with commit c0247d289e73 ("btrfs: send: annotate struct name_cache_entry with __counted_by()") we annotated the variable length array "name" from the name_cache_entry structure with __counted_by() to improve overflow detection. However that alone was not correct, because the length of that array does not match the "name_len" field - it matches that plus 1 to include the NUL string terminator, so that makes a fortified kernel think there's an overflow and report a splat like this:    strcpy: detected buffer overflow: 20 byte write of buffer size 19   WARNING: CPU: 3 PID: 3310 at __fortify_report+0x45/0x50   CPU: 3 UID: 0 PID: 3310 Comm: btrfs Not tainted 6.11.0-prnet #1   Hardware name: CompuLab Ltd.  sbc-ihsw/Intense-PC2 (IPC2), BIOS IPC2_3.330.7 X64 03/15/2018   RIP: 0010:__fortify_report+0x45/0x50   Code: 48 8b 34 (...)   RSP: 0018:ffff97ebc0d6f650 EFLAGS: 00010246   RAX: 7749924ef60fa600 RBX: ffff8bf5446a521a RCX: 0000000000000027   RDX: 00000000ffffdfff RSI: ffff97ebc0d6f548 RDI: ffff8bf84e7a1cc8   RBP: ffff8bf548574080 R08: ffffffffa8c40e10 R09: 0000000000005ffd   R10: 0000000000000004 R11: ffffffffa8c70e10 R12: ffff8bf551eef400   R13: 0000000000000000 R14: 0000000000000013 R15: 00000000000003a8   FS:  00007fae144de8c0(0000) GS:ffff8bf84e780000(0000) knlGS:0000000000000000   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033   CR2: 00007fae14691690 CR3: 00000001027a2003 CR4: 00000000001706f0   Call Trace:    <TASK>    ? __warn+0x12a/0x1d0    ? __fortify_report+0x45/0x50    ? report_bug+0x154/0x1c0    ? handle_bug+0x42/0x70    ? exc_invalid_op+0x1a/0x50    ? asm_exc_invalid_op+0x1a/0x20    ? __fortify_report+0x45/0x50    __fortify_panic+0x9/0x10   __get_cur_name_and_parent+0x3bc/0x3c0    get_cur_path+0x207/0x3b0    send_extent_data+0x709/0x10d0    ? find_parent_nodes+0x22df/0x25d0    ? mas_nomem+0x13/0x90    ? mtree_insert_range+0xa5/0x110    ? btrfs_lru_cache_store+0x5f/0x1e0    ? iterate_extent_inodes+0x52d/0x5a0    process_extent+0xa96/0x11a0    ? __pfx_lookup_backref_cache+0x10/0x10    ? __pfx_store_backref_cache+0x10/0x10    ? __pfx_iterate_backrefs+0x10/0x10    ? __pfx_check_extent_item+0x10/0x10    changed_cb+0x6fa/0x930    ? tree_advance+0x362/0x390    ? memcmp_extent_buffer+0xd7/0x160    send_subvol+0xf0a/0x1520    btrfs_ioctl_send+0x106b/0x11d0    ? __pfx___clone_root_cmp_sort+0x10/0x10    _btrfs_ioctl_send+0x1ac/0x240    btrfs_ioctl+0x75b/0x850    __se_sys_ioctl+0xca/0x150    do_syscall_64+0x85/0x160    ? __count_memcg_events+0x69/0x100    ? handle_mm_fault+0x1327/0x15c0    ? __se_sys_rt_sigprocmask+0xf1/0x180    ? syscall_exit_to_user_mode+0x75/0xa0    ? do_syscall_64+0x91/0x160    ? do_user_addr_fault+0x21d/0x630   entry_SYSCALL_64_after_hwframe+0x76/0x7e   RIP: 0033:0x7fae145eeb4f   Code: 00 48 89 (...)   RSP: 002b:00007ffdf1cb09b0 EFLAGS: 00000246 ORIG_RAX: 0000000000000010   RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 00007fae145eeb4f   RDX: 00007ffdf1cb0ad0 RSI: 0000000040489426 RDI: 0000000000000004   RBP: 00000000000078fe R08: 00007fae144006c0 R09: 00007ffdf1cb0927   R10: 0000000000000008 R11: 0000000000000246 R12: 00007ffdf1cb1ce8   R13: 0000000000000003 R14: 000055c499fab2e0 R15: 0000000000000004    </TASK>  Fix this by not storing the NUL string terminator since we don't actually need it for name cache entries, this way "name_len" corresponds to the actual size of the "name" array. This requires marking the "name" array field with __nonstring and using memcpy() instead of strcpy() as recommended by the guidelines at:     https://github.com/KSPP/linux/issues/90