mm/hugetlb: fix kernel NULL pointer dereference when replacing free hugetlb folios

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

mm/hugetlb: fix kernel NULL pointer dereference when replacing free hugetlb folios

A kernel crash was observed when replacing free hugetlb folios:

BUG: kernel NULL pointer dereference, address: 0000000000000028

PGD 0 P4D 0

Oops: Oops: 0000 [#1] SMP NOPTI

CPU: 28 UID: 0 PID: 29639 Comm: test_cma.sh Tainted 6.15.0-rc6-zp #41 PREEMPT(voluntary)

RIP: 0010:alloc_and_dissolve_hugetlb_folio+0x1d/0x1f0

RSP: 0018:ffffc9000b30fa90 EFLAGS: 00010286

RAX: 0000000000000000 RBX: 0000000000342cca RCX: ffffea0043000000

RDX: ffffc9000b30fb08 RSI: ffffea0043000000 RDI: 0000000000000000

RBP: ffffc9000b30fb20 R08: 0000000000001000 R09: 0000000000000000

R10: ffff88886f92eb00 R11: 0000000000000000 R12: ffffea0043000000

R13: 0000000000000000 R14: 00000000010c0200 R15: 0000000000000004

FS: 00007fcda5f14740(0000) GS:ffff8888ec1d8000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 0000000000000028 CR3: 0000000391402000 CR4: 0000000000350ef0

Call Trace:

<TASK>

replace_free_hugepage_folios+0xb6/0x100

alloc_contig_range_noprof+0x18a/0x590

? srso_return_thunk+0x5/0x5f

? down_read+0x12/0xa0

? srso_return_thunk+0x5/0x5f

cma_range_alloc.constprop.0+0x131/0x290

__cma_alloc+0xcf/0x2c0

cma_alloc_write+0x43/0xb0

simple_attr_write_xsigned.constprop.0.isra.0+0xb2/0x110

debugfs_attr_write+0x46/0x70

full_proxy_write+0x62/0xa0

vfs_write+0xf8/0x420

? srso_return_thunk+0x5/0x5f

? filp_flush+0x86/0xa0

? srso_return_thunk+0x5/0x5f

? filp_close+0x1f/0x30

? srso_return_thunk+0x5/0x5f

? do_dup2+0xaf/0x160

? srso_return_thunk+0x5/0x5f

ksys_write+0x65/0xe0

do_syscall_64+0x64/0x170

entry_SYSCALL_64_after_hwframe+0x76/0x7e

There is a potential race between __update_and_free_hugetlb_folio() and

replace_free_hugepage_folios():

CPU1 CPU2

__update_and_free_hugetlb_folio replace_free_hugepage_folios

folio_test_hugetlb(folio)

-- It's still hugetlb folio.

__folio_clear_hugetlb(folio)

hugetlb_free_folio(folio)

h = folio_hstate(folio)

-- Here, h is NULL pointer

When the above race condition occurs, folio_hstate(folio) returns NULL,

and subsequent access to this NULL pointer will cause the system to crash.

To resolve this issue, execute folio_hstate(folio) under the protection

of the hugetlb_lock lock, ensuring that folio_hstate(folio) does not

return NULL.