{"id":51027,"date":"2026-05-03T02:06:11","date_gmt":"2026-05-03T02:06:11","guid":{"rendered":"http:\/\/localhost\/?p=51027"},"modified":"2026-05-03T02:06:11","modified_gmt":"2026-05-03T02:06:11","slug":"writeback-fix-use-after-free-in-inodeswitchwbsworkfn","status":"publish","type":"post","link":"https:\/\/zero.redgem.net\/?p=51027","title":{"rendered":"writeback: Fix use after free in inode_switch_wbs_work_fn()_CVE-2026-31703"},"content":{"rendered":"<p>{&#8220;lastseen&#8221;:&#8221;&#8221;,&#8221;description&#8221;:&#8221;In the Linux kernel, the following vulnerability has been resolved:\\n\\nwriteback: Fix use after free in inode_switch_wbs_work_fn()\\n\\ninode_switch_wbs_work_fn() has a loop like:\\n\\n  wb_get(new_wb);\\n  while (1) {\\n    list = llist_del_all(\\u0026new_wb-\\u003eswitch_wbs_ctxs);\\n    \/* Nothing to do? *\/\\n    if (!list)\\n      break;\\n    &#8230; process the items &#8230;\\n  }\\n\\nNow adding of items to the list looks like:\\n\\nwb_queue_isw()\\n  if (llist_add(\\u0026isw-\\u003elist, \\u0026wb-\\u003eswitch_wbs_ctxs))\\n    queue_work(isw_wq, \\u0026wb-\\u003eswitch_work);\\n\\nBecause inode_switch_wbs_work_fn() loops when processing isw items, it\\ncan happen that wb-\\u003eswitch_work is pending while wb-\\u003eswitch_wbs_ctxs is\\nempty. This is a problem because in that case wb can get freed (no isw\\nitems -\\u003e no wb reference) while the work is still pending causing\\nuse-after-free issues.\\n\\nWe cannot just fix this by cancelling work when freeing wb because that\\ncould still trigger problematic 0 -\\u003e 1 transitions on wb refcount due to\\nwb_get() in inode_switch_wbs_work_fn(). It could be all handled with\\nmore careful code but that seems unnecessarily complex so let&#8217;s avoid\\nthat until it is proven that the looping actually brings practical\\nbenefit. Just remove the loop from inode_switch_wbs_work_fn() instead.\\nThat way when wb_queue_isw() queues work, we are guaranteed we have\\nadded the first item to wb-\\u003eswitch_wbs_ctxs and nobody is going to\\nremove it (and drop the wb reference it holds) until the queued work\\nruns.&#8221;,&#8221;published&#8221;:&#8221;2026-05-01T13:56:02.415Z&#8221;,&#8221;modified&#8221;:&#8221;2026-05-03T05:45:27.309Z&#8221;,&#8221;type&#8221;:&#8221;cve&#8221;,&#8221;title&#8221;:&#8221;writeback: Fix use after free in inode_switch_wbs_work_fn()&#8221;,&#8221;source&#8221;:&#8221;Linux&#8221;,&#8221;references&#8221;:&#8221;https:\/\/git.kernel.org\/stable\/c\/028103656b84273c73e9e271cf95c9f3421f4b8a\\nhttps:\/\/git.kernel.org\/stable\/c\/9223e5f30403a9b506d6d0bff4f2e29a2d7d46af\\nhttps:\/\/git.kernel.org\/stable\/c\/6689f01d6740cf358932b3e97ee968c6099800d9&#8243;,&#8221;id&#8221;:&#8221;CVE-2026-31703&#8243;,&#8221;bulletinFamily&#8221;:&#8221;&#8221;,&#8221;cwe&#8221;:null,&#8221;cvelist&#8221;:null,&#8221;sourceData&#8221;:&#8221;Linux Linux e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b\\nLinux Linux e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b\\nLinux Linux e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b\\nLinux Linux 6.18&#8243;,&#8221;sourceHref&#8221;:&#8221;&#8221;,&#8221;cvss&#8221;:{&#8220;score&#8221;:7.8,&#8221;severity&#8221;:&#8221;HIGH&#8221;,&#8221;vector&#8221;:&#8221;CVSS:3.1\/AV:L\/AC:L\/PR:L\/UI:N\/S:U\/C:H\/I:H\/A:H&#8221;,&#8221;version&#8221;:&#8221;3.1&#8243;},&#8221;cvss2&#8243;:{},&#8221;cvss3&#8243;:{&#8220;version&#8221;:&#8221;&#8221;,&#8221;vectorString&#8221;:&#8221;&#8221;,&#8221;baseScore&#8221;:0,&#8221;baseSeverity&#8221;:&#8221;&#8221;,&#8221;attackVector&#8221;:&#8221;&#8221;,&#8221;attackComplexity&#8221;:&#8221;&#8221;,&#8221;privilegesRequired&#8221;:&#8221;&#8221;,&#8221;userInteraction&#8221;:&#8221;&#8221;,&#8221;scope&#8221;:&#8221;&#8221;,&#8221;confidentialityImpact&#8221;:&#8221;&#8221;,&#8221;integrityImpact&#8221;:&#8221;&#8221;,&#8221;availabilityImpact&#8221;:&#8221;&#8221;,&#8221;cvssV3&#8243;:{&#8220;version&#8221;:&#8221;&#8221;,&#8221;vectorString&#8221;:&#8221;&#8221;,&#8221;baseScore&#8221;:0,&#8221;baseSeverity&#8221;:&#8221;&#8221;,&#8221;attackVector&#8221;:&#8221;&#8221;,&#8221;attackComplexity&#8221;:&#8221;&#8221;,&#8221;privilegesRequired&#8221;:&#8221;&#8221;,&#8221;userInteraction&#8221;:&#8221;&#8221;,&#8221;scope&#8221;:&#8221;&#8221;,&#8221;confidentialityImpact&#8221;:&#8221;&#8221;,&#8221;integrityImpact&#8221;:&#8221;&#8221;,&#8221;availabilityImpact&#8221;:&#8221;&#8221;}},&#8221;href&#8221;:&#8221;&#8221;,&#8221;category_name&#8221;:&#8221;CVE&#8221;,&#8221;post_link&#8221;:&#8221;&#8221;,&#8221;product&#8221;:&#8221;Linux&#8221;,&#8221;version&#8221;:&#8221;e1b849cfa6b61f1c866a908c9e8dd9b5aaab820b&#8221;,&#8221;vendor&#8221;:&#8221;Linux&#8221;,&#8221;ai_description&#8221;:&#8221;&#8221;,&#8221;ai_severity&#8221;:&#8221;&#8221;,&#8221;ai_vendor&#8221;:&#8221;&#8221;,&#8221;ai_product&#8221;:&#8221;&#8221;,&#8221;ai_version&#8221;:&#8221;&#8221;,&#8221;ai_score&#8221;:0}<\/p>\n","protected":false},"excerpt":{"rendered":"<p>{&#8220;lastseen&#8221;:&#8221;&#8221;,&#8221;description&#8221;:&#8221;In the Linux kernel, the following vulnerability has been resolved:\\n\\nwriteback: Fix use after free in inode_switch_wbs_work_fn()\\n\\ninode_switch_wbs_work_fn() has a loop like:\\n\\n wb_get(new_wb);\\n while (1) {\\n list&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[6,8,28,12,15,13,7,11,5],"class_list":["post-51027","post","type-post","status-publish","format-standard","hentry","category-category_cve","tag-cve","tag-cvss","tag-cvss-78","tag-exploit","tag-high","tag-news","tag-security","tag-tapic","tag-vulnerability"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.5 - 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