 skbuff: Fix a race between coalescing and releasing SKBs · gregkh/linux@5f692c9 · GitHub Skip to content Navigation Menu Toggle navigation Sign in Appearance settings Platform AI CODE CREATION GitHub Copilot Write better code with AI GitHub Spark Build and deploy intelligent apps GitHub Models Manage and compare prompts MCP Registry New Integrate external tools DEVELOPER WORKFLOWS Actions Automate any workflow Codespaces Instant dev environments Issues Plan and track work Code Review Manage code changes APPLICATION SECURITY GitHub Advanced Security Find and fix vulnerabilities Code security Secure your code as you build Secret protection  EXPLORE Why GitHub Documentation Blog Changelog Marketplace View all features Solutions BY COMPANY SIZE Enterprises Small and medium teams Startups Nonprofits BY USE CASE App Modernization DevSecOps DevOps CI/CD View all use cases BY INDUSTRY Healthcare Financial services Manufacturing Government View all industries View all solutions Resources EXPLORE BY TOPIC AI Software Development DevOps Security View all topics EXPLORE BY TYPE Customer stories Events &amp; webinars Ebooks &amp; reports Business insights GitHub Skills SUPPORT &amp; SERVICES Documentation Customer support Community forum Trust center Partners View all resources Open Source COMMUNITY GitHub Sponsors Fund open source developers PROGRAMS Security Lab Maintainer Community Accelerator GitHub Stars Archive Program REPOSITORIES Topics Trending Collections Enterprise ENTERPRISE SOLUTIONS Enterprise platform AI-powered developer platform AVAILABLE ADD-ONS GitHub Advanced Security Enterprise-grade security features Copilot for Business Enterprise-grade AI features Premium Support Enterprise-grade 24/7 support Pricing Search or jump to... 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Dismiss alert {{ message }} gregkh / linux Public Notifications You must be signed in to change notification settings Fork 676 Star 636 Code Actions Security and quality 0 Insights Additional navigation options Code Actions Security and quality Insights Commit 5f692c9 Browse files Browse files LiangChen77 authored and gregkh committed skbuff: Fix a race between coalescing and releasing SKBs [ Upstream commit 0646dc3 ] Commit 1effe8c ("skbuff: fix coalescing for page_pool fragment recycling") allowed coalescing to proceed with non page pool page and page pool page when @from is cloned, i.e. to-&gt;pp_recycle --&gt; false from-&gt;pp_recycle --&gt; true skb_cloned(from) --&gt; true However, it actually requires skb_cloned( @from ) to hold true until coalescing finishes in this situation. If the other cloned SKB is released while the merging is in process, from_shinfo-&gt;nr_frags will be set to 0 toward the end of the function, causing the increment of frag page _refcount to be unexpectedly skipped resulting in inconsistent reference counts. Later when SKB( @to ) is released, it frees the page directly even though the page pool page is still in use, leading to use-after-free or double-free errors. So it should be prohibited. The double-free error message below prompted us to investigate: BUG: Bad page state in process swapper/1 pfn:0e0d1 page:00000000c6548b28 refcount:-1 mapcount:0 mapping:0000000000000000 index:0x2 pfn:0xe0d1 flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff) raw: 000fffffc0000000 0000000000000000 ffffffff00000101 0000000000000000 raw: 0000000000000002 0000000000000000 ffffffffffffffff 0000000000000000 page dumped because: nonzero _refcount CPU: 1 PID: 0 Comm: swapper/1 Tainted: G E 6.2.0+ Call Trace: &lt;IRQ&gt; dump_stack_lvl+0x32/0x50 bad_page+0x69/0xf0 free_pcp_prepare+0x260/0x2f0 free_unref_page+0x20/0x1c0 skb_release_data+0x10b/0x1a0 napi_consume_skb+0x56/0x150 net_rx_action+0xf0/0x350 ? __napi_schedule+0x79/0x90 __do_softirq+0xc8/0x2b1 __irq_exit_rcu+0xb9/0xf0 common_interrupt+0x82/0xa0 &lt;/IRQ&gt; &lt;TASK&gt; asm_common_interrupt+0x22/0x40 RIP: 0010:default_idle+0xb/0x20 Fixes: 53e0961 ("page_pool: add frag page recycling support in page pool") Signed-off-by: Liang Chen &lt;liangchen.linux@gmail.com&gt; Reviewed-by: Eric Dumazet &lt;edumazet@google.com&gt; Link: https://lore.kernel.org/r/20230413090353.14448-1-liangchen.linux@gmail.com Signed-off-by: Jakub Kicinski &lt;kuba@kernel.org&gt; Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt; 1 parent 5dcf3a6 commit 5f692c9 Copy full SHA for 5f692c9 1 file changed + 8 - 8 Lines changed: 8 additions &amp; 8 deletions File tree Expand file tree Collapse file tree Open diff view settings Filter options net/core skbuff.c Expand file tree Collapse file tree Open diff view settings Collapse file ‎ net/core/skbuff.c ‎ Copy file name to clipboard Expand all lines: net/core/skbuff.c + 8 - 8 Lines changed: 8 additions &amp; 8 deletions Original file line number Diff line number Diff line change @@ -5475,18 +5475,18 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from, 5475 5475 if ( skb_cloned ( to )) 5476 5476 return false; 5477 5477 5478 - /* In general, avoid mixing slab allocated and page_pool allocated 5479 - * pages within the same SKB. However when @to is not pp_recycle and 5480 - * @from is cloned, we can transition frag pages from page_pool to 5481 - * reference counted. 5482 - * 5483 - * On the other hand, don&#39;t allow coalescing two pp_recycle SKBs if 5484 - * @from is cloned, in case the SKB is using page_pool fragment 5478 + /* In general, avoid mixing page_pool and non-page_pool allocated 5479 + * pages within the same SKB. Additionally avoid dealing with clones 5480 + * with page_pool pages, in case the SKB is using page_pool fragment 5485 5481 * references (PP_FLAG_PAGE_FRAG). Since we only take full page 5486 5482 * references for cloned SKBs at the moment that would result in 5487 5483 * inconsistent reference counts. 5484 + * In theory we could take full references if @from is cloned and 5485 + * !@to-&gt;pp_recycle but its tricky (due to potential race with 5486 + * the clone disappearing) and rare, so not worth dealing with. 5488 5487 */ 5489 - if ( to -&gt; pp_recycle != ( from -&gt; pp_recycle &amp;&amp; ! skb_cloned ( from ))) 5488 + if ( to -&gt; pp_recycle != from -&gt; pp_recycle || 5489 + ( from -&gt; pp_recycle &amp;&amp; skb_cloned ( from ))) 5490 5490 return false; 5491 5491 5492 5492 if ( len &lt;= skb_tailroom ( to )) { 0 commit comments Comments 0 ( 0 ) Footer &copy; 2026 GitHub,&nbsp;Inc. Footer navigation Terms Privacy Security Status Community Docs Contact Manage cookies Do not share my personal information You can’t perform that action at this time. 