Subject: CVE-2024-49934: fs/inode: Prevent dump_mapping() accessing invalid dentry.d_name.name

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

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

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

fs/inode: Prevent dump_mapping() accessing invalid dentry.d_name.name

It's observed that a crash occurs during hot-remove a memory device,
in which user is accessing the hugetlb. See calltrace as following:

------------[ cut here ]------------
WARNING: CPU: 1 PID: 14045 at arch/x86/mm/fault.c:1278 do_user_addr_fault+0x2a0/0x790
Modules linked in: kmem device_dax cxl_mem cxl_pmem cxl_port cxl_pci dax_hmem dax_pmem nd_pmem cxl_acpi nd_btt cxl_core crc32c_intel nvme virtiofs fuse nvme_core nfit libnvdimm dm_multipath scsi_dh_rdac scsi_dh_emc s
mirror dm_region_hash dm_log dm_mod
CPU: 1 PID: 14045 Comm: daxctl Not tainted 6.10.0-rc2-lizhijian+ #492
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:do_user_addr_fault+0x2a0/0x790
Code: 48 8b 00 a8 04 0f 84 b5 fe ff ff e9 1c ff ff ff 4c 89 e9 4c 89 e2 be 01 00 00 00 bf 02 00 00 00 e8 b5 ef 24 00 e9 42 fe ff ff <0f> 0b 48 83 c4 08 4c 89 ea 48 89 ee 4c 89 e7 5b 5d 41 5c 41 5d 41
RSP: 0000:ffffc90000a575f0 EFLAGS: 00010046
RAX: ffff88800c303600 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000001000 RSI: ffffffff82504162 RDI: ffffffff824b2c36
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffc90000a57658
R13: 0000000000001000 R14: ffff88800bc2e040 R15: 0000000000000000
FS:  00007f51cb57d880(0000) GS:ffff88807fd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000001000 CR3: 00000000072e2004 CR4: 00000000001706f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ? __warn+0x8d/0x190
 ? do_user_addr_fault+0x2a0/0x790
 ? report_bug+0x1c3/0x1d0
 ? handle_bug+0x3c/0x70
 ? exc_invalid_op+0x14/0x70
 ? asm_exc_invalid_op+0x16/0x20
 ? do_user_addr_fault+0x2a0/0x790
 ? exc_page_fault+0x31/0x200
 exc_page_fault+0x68/0x200
<...snip...>
BUG: unable to handle page fault for address: 0000000000001000
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 800000000ad92067 P4D 800000000ad92067 PUD 7677067 PMD 0
 Oops: Oops: 0000 [#1] PREEMPT SMP PTI
 ---[ end trace 0000000000000000 ]---
 BUG: unable to handle page fault for address: 0000000000001000
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 800000000ad92067 P4D 800000000ad92067 PUD 7677067 PMD 0
 Oops: Oops: 0000 [#1] PREEMPT SMP PTI
 CPU: 1 PID: 14045 Comm: daxctl Kdump: loaded Tainted: G        W          6.10.0-rc2-lizhijian+ #492
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
 RIP: 0010:dentry_name+0x1f4/0x440
<...snip...>
? dentry_name+0x2fa/0x440
vsnprintf+0x1f3/0x4f0
vprintk_store+0x23a/0x540
vprintk_emit+0x6d/0x330
_printk+0x58/0x80
dump_mapping+0x10b/0x1a0
? __pfx_free_object_rcu+0x10/0x10
__dump_page+0x26b/0x3e0
? vprintk_emit+0xe0/0x330
? _printk+0x58/0x80
? dump_page+0x17/0x50
dump_page+0x17/0x50
do_migrate_range+0x2f7/0x7f0
? do_migrate_range+0x42/0x7f0
? offline_pages+0x2f4/0x8c0
offline_pages+0x60a/0x8c0
memory_subsys_offline+0x9f/0x1c0
? lockdep_hardirqs_on+0x77/0x100
? _raw_spin_unlock_irqrestore+0x38/0x60
device_offline+0xe3/0x110
state_store+0x6e/0xc0
kernfs_fop_write_iter+0x143/0x200
vfs_write+0x39f/0x560
ksys_write+0x65/0xf0
do_syscall_64+0x62/0x130

Previously, some sanity check have been done in dump_mapping() before
the print facility parsing '%pd' though, it's still possible to run into
an invalid dentry.d_name.name.

Since dump_mapping() only needs to dump the filename only, retrieve it
by itself in a safer way to prevent an unnecessary crash.

Note that either retrieving the filename with '%pd' or
strncpy_from_kernel_nofault(), the filename could be unreliable.

The Linux kernel CVE team has assigned CVE-2024-49934 to this issue.

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

	Fixed in 6.10.14 with commit f92b8829c6e7
	Fixed in 6.11.3 with commit ef921bc72328
	Fixed in 6.12-rc1 with commit 7f7b850689ac

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-2024-49934
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/inode.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/f92b8829c6e75632de4e2b9f70e7a7e6c5c2ba98
	https://git.kernel.org/stable/c/ef921bc72328b577cb45772ff7921cba4773b74a
	https://git.kernel.org/stable/c/7f7b850689ac06a62befe26e1fd1806799e7f152