CVE-2026-63819: f2fs: fix to do sanity check on f2fs_get_node_folio_ra()

CVE-2026-63819: f2fs: fix to do sanity check on f2fs_get_node_folio_ra()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

In the Linux kernel, the following vulnerability has been resolved:

f2fs: fix to do sanity check on f2fs_get_node_folio_ra()

kernel BUG at fs/f2fs/file.c:845!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5336 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:f2fs_do_truncate_blocks+0x1115/0x1140 fs/f2fs/file.c:845
Code: fc fc 90 0f 0b e8 8b 9d 9a fd 90 0f 0b e8 83 9d 9a fd 48 89 df 48 c7 c6 60 d1 1a 8c e8 54 f1 fc fc 90 0f 0b e8 6c 9d 9a fd 90 <0f> 0b e8 64 9d 9a fd 90 0f 0b 90 e9 93 fd ff ff e8 56 9d 9a fd 90
RSP: 0018:ffffc9000e4474c0 EFLAGS: 00010283
RAX: ffffffff842b1d34 RBX: 0000000000000003 RCX: 0000000000100000
RDX: ffffc9000f03a000 RSI: 0000000000035503 RDI: 0000000000035504
RBP: ffffc9000e447608 R08: ffff8880123b0000 R09: 0000000000000002
R10: 00000000fffffffe R11: 0000000000000002 R12: 0000000000000001
R13: 0000000000000000 R14: 1ffff92001c88ea0 R15: 00000000ffff039c
FS:  00007f7e02ee36c0(0000) GS:ffff88808c887000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff0305c4000 CR3: 0000000012d4c000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 f2fs_truncate_blocks+0x10a/0x300 fs/f2fs/file.c:882
 f2fs_truncate+0x471/0x7c0 fs/f2fs/file.c:940
 f2fs_evict_inode+0xa3f/0x1ac0 fs/f2fs/inode.c:907
 evict+0x61e/0xb10 fs/inode.c:841
 f2fs_fill_super+0x5f43/0x78f0 fs/f2fs/super.c:5224
 get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
 vfs_get_tree+0x92/0x2a0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3758 [inline]
 do_new_mount+0x341/0xd30 fs/namespace.c:3834
 do_mount fs/namespace.c:4167 [inline]
 __do_sys_mount fs/namespace.c:4383 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4360
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

	count = ADDRS_PER_PAGE(dn.node_folio, inode);

	count -= dn.ofs_in_node;
	f2fs_bug_on(sbi, count < 0);

The fuzz test will trigger above bug_on in f2fs.

The root cause should be: in the corrupted inode, there is a direct node
which has the same ino and nid in its footer, so in f2fs_do_truncate_blocks(),
after f2fs_get_dnode_of_data() finds such dnode:
1) ADDRS_PER_PAGE(dn.node_folio, inode) will return 923
2) once dn.ofs_in_node points to addr[923, 1017]
Then it will trigger the system panic.

Let's introduce NODE_TYPE_NON_IXNODE to indicate current node should
not be an inode or xattr node, and then use it in below path to detect
inconsistent node chain in inode mapping table:

- f2fs_do_truncate_blocks
 - f2fs_get_dnode_of_data
  - f2fs_get_node_folio_ra
   -  __get_node_folio
    - f2fs_sanity_check_node_footer
     - case NODE_TYPE_NON_IXNODE -> check whether it is inode|xnode

The Linux kernel CVE team has assigned CVE-2026-63819 to this issue.


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

	Fixed in 6.18.39 with commit 406c28af75123432d38cf9bbaa6f1476f7b14770
	Fixed in 7.1.3 with commit 0cc21c1ffe15b4156b0bf744f32fd1faef0b7c73
	Fixed in 7.2-rc1 with commit 8712353ed80f87271d732297567dcdbe4b84e8c7

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-2026-63819
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/f2fs/f2fs.h
	fs/f2fs/node.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/406c28af75123432d38cf9bbaa6f1476f7b14770
	https://git.kernel.org/stable/c/0cc21c1ffe15b4156b0bf744f32fd1faef0b7c73
	https://git.kernel.org/stable/c/8712353ed80f87271d732297567dcdbe4b84e8c7