CVE: CVE-2024-49934
Published: 2024-10-21
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: [PII_REDACTED] RCX: [PII_REDACTED]
RDX: [PII_REDACTED] RSI: ffffffff82504162 RDI: ffffffff824b2c36
RBP: [PII_REDACTED] R08: [PII_REDACTED] R09: [PII_REDACTED]
R10: [PII_REDACTED] R11: [PII_REDACTED] R12: ffffc90000a57658
R13: [PII_REDACTED] R14: ffff88800bc2e040 R15: [PII_REDACTED]
FS:  00007f51cb57d880(0000) GS:ffff88807fd00000(0000) knlGS:[PII_REDACTED]
CS:  0010 DS: 0000 ES: 0000 CR0: [PII_REDACTED]
CR2: [PII_REDACTED] CR3:[PII_REDACTED]2e2004 CR4:[PII_REDACTED]1706f0
DR0: [PII_REDACTED] DR1: [PII_REDACTED] DR2: [PII_REDACTED]
DR3: [PII_REDACTED] DR6: 00000000fffe0ff0 DR7: [PII_REDACTED]
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: [PII_REDACTED]
 #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 [PII_REDACTED] ]---
 BUG: unable to handle page fault for address: [PII_REDACTED]
 #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.
CVSS Score: 4.6 (MEDIUM)
References: https://git.kernel.org/stable/c/1a4159138e718db6199f0abf376ad52f726dcc5c; https://git.kernel.org/stable/c/7f7b850689ac06a62befe26e1fd1806799e7f152; https://git.kernel.org/stable/c/e0f6ee75f50476607ca82fc7c3711c795ce09b52