Subject: CVE-2024-49869: btrfs: send: fix buffer overflow detection when copying path to cache entry

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

The Linux kernel CVE team has assigned CVE-2024-49869 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.11 with commit c0247d289e73 and fixed in 6.11.3 with commit 843738ede6cb
	Issue introduced in 6.11 with commit c0247d289e73 and fixed in 6.12-rc2 with commit 96c6ca71572a

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-49869
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/btrfs/send.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/843738ede6cb8b959fb22591fcbabe8b456d7216
	https://git.kernel.org/stable/c/96c6ca71572a3556ed0c37237305657ff47174b7