CVE-2021-47635

一、漏洞信息
 漏洞编号：[CVE-2021-47635](https://nvd.nist.gov/vuln/detail/CVE-2021-47635)
 漏洞归属组件：[kernel](https://gitee.com/src-openeuler/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
<details>
<summary>更多参考(点击展开)</summary>

| 参考来源 | 参考链接 | 来源链接 |
| ------- | -------- | -------- |
| 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | https://git.kernel.org/stable/c/3b67db8a6ca83e6ff90b756d3da0c966f61cd37b |  |
| 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | https://git.kernel.org/stable/c/4f75bab98565afd4f905059c56ec4caba88a7eec |  |
| 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | https://git.kernel.org/stable/c/5aaa2c0f0052b02c4a982993d4c5bb68fb7cbe22 |  |
| 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | https://git.kernel.org/stable/c/c34ae24a2590fee96a3a7735ba2fa6cc52306221 |  |
| 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | https://git.kernel.org/stable/c/fbeb2139eed65e929ce806c6468e6601ade01b1b |  |
| suse_bugzilla | http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-47635 | https://bugzilla.suse.com/show_bug.cgi?id=1237759 |
| suse_bugzilla | https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2021/CVE-2021-47635.mbox | https://bugzilla.suse.com/show_bug.cgi?id=1237759 |
| suse_bugzilla | https://git.kernel.org/stable/c/c34ae24a2590fee96a3a7735ba2fa6cc52306221 | https://bugzilla.suse.com/show_bug.cgi?id=1237759 |
| suse_bugzilla | https://git.kernel.org/stable/c/4f75bab98565afd4f905059c56ec4caba88a7eec | https://bugzilla.suse.com/show_bug.cgi?id=1237759 |
| suse_bugzilla | https://git.kernel.org/stable/c/5aaa2c0f0052b02c4a982993d4c5bb68fb7cbe22 | https://bugzilla.suse.com/show_bug.cgi?id=1237759 |
| suse_bugzilla | https://git.kernel.org/stable/c/fbeb2139eed65e929ce806c6468e6601ade01b1b | https://bugzilla.suse.com/show_bug.cgi?id=1237759 |
| suse_bugzilla | https://git.kernel.org/stable/c/3b67db8a6ca83e6ff90b756d3da0c966f61cd37b | https://bugzilla.suse.com/show_bug.cgi?id=1237759 |

</details>

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：
  <details>
<summary>详情(点击展开)</summary>

无
</details>

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.master(6.6.0):不受影响
3.openEuler-22.03-LTS-SP3(5.10.0):不受影响
4.openEuler-22.03-LTS-SP4(5.10.0):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):不受影响

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

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

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