一、漏洞信息
漏洞编号：CVE-2021-47635
漏洞归属组件：kernel
漏洞归属的版本：4.19.140,4.19.194,4.19.90,5.10.0,6.1.19,6.1.8,6.4.0,6.6.0
CVSS V3.0分值：
BaseScore：5.5 Medium
Vector：CVSS：3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
漏洞简述：
In the Linux kernel, the following vulnerability has been resolved:ubifs: Fix to add refcount once page is set privateMM defined the rule [1] very clearly that once page was set with PG_privateflag, we should increment the refcount in that page, also main flows likepageout(), migrate_page() will assume there is one additional pagereference count if page_has_private() returns true. Otherwise, we mayget a BUG in page migration: page:0000000080d05b9d refcount:-1 mapcount:0 mapping:000000005f4d82a8 index:0xe2 pfn:0x14c12 aops:ubifs_file_address_operations [ubifs] ino:8f1 dentry name: f30e flags: 0x1fffff80002405(locked|uptodate|owner_priv_1|private|node=0| zone=1|lastcpupid=0x1fffff) page dumped because: VM_BUG_ON_PAGE(page_count(page) != 0) ------------[ cut here ]------------ kernel BUG at include/linux/page_ref.h:184! invalid opcode: 0000 [#1] SMP CPU: 3 PID: 38 Comm: kcompactd0 Not tainted 5.15.0-rc5 RIP: 0010:migrate_page_move_mapping+0xac3/0xe70 Call Trace: ubifs_migrate_page+0x22/0xc0 [ubifs] move_to_new_page+0xb4/0x600 migrate_pages+0x1523/0x1cc0 compact_zone+0x8c5/0x14b0 kcompactd+0x2bc/0x560 kthread+0x18c/0x1e0 ret_from_fork+0x1f/0x30Before the time, we should make clean a concept, what does refcount meansin page gotten from grab_cache_page_write_begin(). There are 2 situations:Situation 1: refcount is 3, page is created by __page_cache_alloc. TYPE_A - the write process is using this page TYPE_B - page is assigned to one certain mapping by calling __add_to_page_cache_locked() TYPE_C - page is added into pagevec list corresponding current cpu by calling lru_cache_add()Situation 2: refcount is 2, page is gotten from the mapping s tree TYPE_B - page has been assigned to one certain mapping TYPE_A - the write process is using this page (by calling page_cache_get_speculative())Filesystem releases one refcount by calling put_page() in xxx_write_end(),the released refcount corresponds to TYPE_A (write task is using it). Ifthere are any processes using a page, page migration process will skip thepage by judging whether expected_page_refs() equals to page refcount.The BUG is caused by following process: PA(cpu 0) kcompactd(cpu 1) compact_zoneubifs_write_begin page_a = grab_cache_page_write_begin add_to_page_cache_lru lru_cache_add pagevec_add // put page into cpu 0 s pagevec (refcnf = 3, for page creation process)ubifs_write_end SetPagePrivate(page_a) // doesn t increase page count ! unlock_page(page_a) put_page(page_a) // refcnt = 2 [...] PB(cpu 0)filemap_read filemap_get_pages add_to_page_cache_lru lru_cache_add __pagevec_lru_add // traverse all pages in cpu 0 s pagevec __pagevec_lru_add_fn SetPageLRU(page_a) isolate_migratepages isolate_migratepages_block get_page_unless_zero(page_a) // refcnt = 3 list_add(page_a, from_list) migrate_pages(from_list) __unmap_and_move move_to_new_page ubifs_migrate_page(page_a) migrate_page_move_mapping expected_page_refs get 3 (migration[1] + mapping[1] + private[1]) release_pages put_page_testzero(page_a) // refcnt = 3 page_ref_freeze // refcnt = 0 page_ref_dec_and_test(0 - 1 = -1) page_ref_unfreeze VM_BUG_ON_PAGE(-1 != 0, page)UBIFS doesn t increase the page refcount after setting private flag, whichleads to page migration task believes the page is not used by any otherprocesses, so the page is migrated. This causes concurrent accessing onpage refcount between put_page() called by other process(eg. read processcalls lru_cache_add) and page_ref_unfreeze() called by mi---truncated---
漏洞公开时间：2025-02-26 14:37:05
漏洞创建时间：2025-02-26 16:58:06
漏洞详情参考链接：
https://nvd.nist.gov/vuln/detail/CVE-2021-47635

漏洞分析指导链接：
https://gitee.com/openeuler/cve-manager/blob/master/cve-vulner-manager/doc/md/manual.md
漏洞数据来源:
openBrain开源漏洞感知系统
漏洞补丁信息：

二、漏洞分析结构反馈
影响性分析说明：
In the Linux kernel, the following vulnerability has been resolved:ubifs: Fix to add refcount once page is set privateMM defined the rule [1] very clearly that once page was set with PG_privateflag, we should increment the refcount in that page, also main flows likepageout(), migrate_page() will assume there is one additional pagereference count if page_has_private() returns true. Otherwise, we mayget a BUG in page migration: page:0000000080d05b9d refcount:-1 mapcount:0 mapping:000000005f4d82a8 index:0xe2 pfn:0x14c12 aops:ubifs_file_address_operations [ubifs] ino:8f1 dentry name: f30e flags: 0x1fffff80002405(locked|uptodate|owner_priv_1|private|node=0| zone=1|lastcpupid=0x1fffff) page dumped because: VM_BUG_ON_PAGE(page_count(page) != 0) ------------[ cut here ]------------ kernel BUG at include/linux/page_ref.h:184! invalid opcode: 0000 [#1] SMP CPU: 3 PID: 38 Comm: kcompactd0 Not tainted 5.15.0-rc5 RIP: 0010:migrate_page_move_mapping+0xac3/0xe70 Call Trace: ubifs_migrate_page+0x22/0xc0 [ubifs] move_to_new_page+0xb4/0x600 migrate_pages+0x1523/0x1cc0 compact_zone+0x8c5/0x14b0 kcompactd+0x2bc/0x560 kthread+0x18c/0x1e0 ret_from_fork+0x1f/0x30Before the time, we should make clean a concept, what does refcount meansin page gotten from grab_cache_page_write_begin(). There are 2 situations:Situation 1: refcount is 3, page is created by __page_cache_alloc. TYPE_A - the write process is using this page TYPE_B - page is assigned to one certain mapping by calling __add_to_page_cache_locked() TYPE_C - page is added into pagevec list corresponding current cpu by calling lru_cache_add()Situation 2: refcount is 2, page is gotten from the mapping s tree TYPE_B - page has been assigned to one certain mapping TYPE_A - the write process is using this page (by calling page_cache_get_speculative())Filesystem releases one refcount by calling put_page() in xxx_write_end(),the released refcount corresponds to TYPE_A (write task is using it). Ifthere are any processes using a page, page migration process will skip thepage by judging whether expected_page_refs() equals to page refcount.The BUG is caused by following process: PA(cpu 0) kcompactd(cpu 1)compact_zoneubifs_write_begin page_a = grab_cache_page_write_begin add_to_page_cache_lru lru_cache_add pagevec_add // put page into cpu 0 s pagevec (refcnf = 3, for page creation process)ubifs_write_end SetPagePrivate(page_a) // doesn t increase page count ! unlock_page(page_a) put_page(page_a) // refcnt = 2[...] PB(cpu 0)filemap_read filemap_get_pages add_to_page_cache_lru lru_cache_add __pagevec_lru_add // traverse all pages in cpu 0 s pagevec __pagevec_lru_add_fn SetPageLRU(page_a)isolate_migratepages isolate_migratepages_block get_page_unless_zero(page_a) // refcnt = 3 list_add(page_a, from_list)migrate_pages(from_list) __unmap_and_move move_to_new_page ubifs_migrate_page(page_a) migrate_page_move_mapping expected_page_refs get 3 (migration[1] + mapping[1] + private[1]) release_pages put_page_testzero(page_a) // refcnt = 3 page_ref_freeze // refcnt = 0 page_ref_dec_and_test(0 - 1 = -1) page_ref_unfreeze VM_BUG_ON_PAGE(-1 != 0, page)UBIFS doesn t increase the page refcount after setting private flag, whichleads to page migration task believes the page is not used by any otherprocesses, so the page is migrated. This causes concurrent accessing onpage refcount between put_page() called by other process(eg. read processcalls lru_cache_add) and page_ref_unfreeze() called by mi---truncated---
openEuler评分：
6.4
Vector：CVSS：3.0/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
受影响版本排查(受影响/不受影响)：
1.openEuler-20.03-LTS-SP4(4.19.90):受影响
2.openEuler-22.03-LTS-SP3(5.10.0):不受影响
3.openEuler-22.03-LTS-SP4(5.10.0):不受影响
4.master(6.6.0):不受影响
5.openEuler-24.03-LTS(6.6.0):不受影响
6.openEuler-24.03-LTS-Next(6.6.0):不受影响
7.openEuler-24.03-LTS-SP1(6.6.0):不受影响
8.openEuler-24.03-LTS-SP2(6.6.0):

修复是否涉及abi变化(是/否)：
1.openEuler-20.03-LTS-SP4(4.19.90):否
2.openEuler-22.03-LTS-SP3(5.10.0):否
3.master(6.6.0):否
4.openEuler-24.03-LTS(6.6.0):否
5.openEuler-24.03-LTS-Next(6.6.0):否
6.openEuler-22.03-LTS-SP4(5.10.0):否
7.openEuler-24.03-LTS-SP1(6.6.0):否
8.openEuler-24.03-LTS-SP2(6.6.0):

原因说明：
1.openEuler-20.03-LTS-SP4(4.19.90):正常修复
2.master(6.6.0):不受影响-漏洞代码不能被攻击者触发
3.openEuler-24.03-LTS-Next(6.6.0):不受影响-漏洞代码不能被攻击者触发
4.openEuler-22.03-LTS-SP3(5.10.0):不受影响-漏洞代码不存在
5.openEuler-22.03-LTS-SP4(5.10.0):不受影响-漏洞代码不存在
6.openEuler-24.03-LTS(6.6.0):不受影响-漏洞代码不存在
7.openEuler-24.03-LTS-SP1(6.6.0):不受影响-漏洞代码不存在
8.openEuler-24.03-LTS-SP2(6.6.0):