CVE-2021-47492

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

mm, thp: bail out early in collapse_file for writeback page

Currently collapse_file does not explicitly check PG_writeback, instead,

page_has_private and try_to_release_page are used to filter writeback

pages. This does not work for xfs with blocksize equal to or larger

than pagesize, because in such case xfs has no page->private.

This makes collapse_file bail out early for writeback page. Otherwise,

xfs end_page_writeback will panic as follows.

page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:ffff0003f88c86a8 index:0x0 pfn:0x84ef32

aops:xfs_address_space_operations [xfs] ino:30000b7 dentry name:"libtest.so"

flags: 0x57fffe0000008027(locked|referenced|uptodate|active|writeback)

raw: 57fffe0000008027 ffff80001b48bc28 ffff80001b48bc28 ffff0003f88c86a8

raw: 0000000000000000 0000000000000000 00000000ffffffff ffff0000c3e9a000

page dumped because: VM_BUG_ON_PAGE(((unsigned int) page_ref_count(page) + 127u <= 127u))

page->mem_cgroup:ffff0000c3e9a000

------------[ cut here ]------------

kernel BUG at include/linux/mm.h:1212!

Internal error: Oops - BUG: 0 [#1] SMP

Modules linked in:

BUG: Bad page state in process khugepaged pfn:84ef32

xfs(E)

page:fffffe00201bcc80 refcount:0 mapcount:0 mapping:0 index:0x0 pfn:0x84ef32

libcrc32c(E) rfkill(E) aes_ce_blk(E) crypto_simd(E) ...

CPU: 25 PID: 0 Comm: swapper/25 Kdump: loaded Tainted: ...

pstate: 60400005 (nZCv daif +PAN -UAO -TCO BTYPE=--)

Call trace:

end_page_writeback+0x1c0/0x214

iomap_finish_page_writeback+0x13c/0x204

iomap_finish_ioend+0xe8/0x19c

iomap_writepage_end_bio+0x38/0x50

bio_endio+0x168/0x1ec

blk_update_request+0x278/0x3f0

blk_mq_end_request+0x34/0x15c

virtblk_request_done+0x38/0x74 [virtio_blk]

blk_done_softirq+0xc4/0x110

__do_softirq+0x128/0x38c

__irq_exit_rcu+0x118/0x150

irq_exit+0x1c/0x30

__handle_domain_irq+0x8c/0xf0

gic_handle_irq+0x84/0x108

el1_irq+0xcc/0x180

arch_cpu_idle+0x18/0x40

default_idle_call+0x4c/0x1a0

cpuidle_idle_call+0x168/0x1e0

do_idle+0xb4/0x104

cpu_startup_entry+0x30/0x9c

secondary_start_kernel+0x104/0x180

Code: d4210000 b0006161 910c8021 94013f4d (d4210000)

---[ end trace 4a88c6a074082f8c ]---

Kernel panic - not syncing: Oops - BUG: Fatal exception in interrupt