{"id":"CVE-2026-43503","summary":"net: skbuff: propagate shared-frag marker through frag-transfer helpers","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: skbuff: propagate shared-frag marker through frag-transfer helpers\n\nTwo frag-transfer helpers (__pskb_copy_fclone() and skb_shift()) fail\nto propagate the SKBFL_SHARED_FRAG bit in skb_shinfo()-\u003eflags when\nmoving frags from source to destination.  __pskb_copy_fclone() defers\nthe rest of the shinfo metadata to skb_copy_header() after copying\nfrag descriptors, but that helper only carries over gso_{size,segs,\ntype} and never touches skb_shinfo()-\u003eflags; skb_shift() moves frag\ndescriptors directly and leaves flags untouched.  As a result, the\ndestination skb keeps a reference to the same externally-owned or\npage-cache-backed pages while reporting skb_has_shared_frag() as\nfalse.\n\nThe mismatch is harmful in any in-place writer that uses\nskb_has_shared_frag() to decide whether shared pages must be detoured\nthrough skb_cow_data().  ESP input is one such writer (esp4.c,\nesp6.c), and a single nft 'dup to \u003clocal\u003e' rule -- or any other\nnf_dup_ipv4() / xt_TEE caller -- is enough to land a pskb_copy()'d\nskb in esp_input() with the marker stripped, letting an unprivileged\nuser write into the page cache of a root-owned read-only file via\nauthencesn-ESN stray writes.\n\nSet SKBFL_SHARED_FRAG on the destination whenever frag descriptors\nwere actually moved from the source.  skb_copy() and skb_copy_expand()\nshare skb_copy_header() too but linearize all paged data into freshly\nallocated head storage and emerge with nr_frags == 0, so\nskb_has_shared_frag() returns false on its own; they need no change.\n\nThe same omission exists in skb_gro_receive() and skb_gro_receive_list().\nThe former moves the incoming skb's frag descriptors into the\naccumulator's last sub-skb via two paths (a direct frag-move loop and\nthe head_frag + memcpy path); the latter chains the incoming skb whole\nonto p's frag_list.  Downstream skb_segment() reads only\nskb_shinfo(p)-\u003eflags, and skb_segment_list() reuses each sub-skb's\nshinfo as the nskb -- both p and lp must carry the marker.\n\nThe same omission also exists in tcp_clone_payload(), which builds an\nMTU probe skb by moving frag descriptors from skbs on sk_write_queue\ninto a freshly allocated nskb.  The helper falls into the same family\nand warrants the same fix for consistency; no TCP TX-side in-place\nwriter is currently known to reach a user page through this gap, but\na future consumer depending on the marker would regress silently.\n\nThe same omission exists in skb_segment(): the per-iteration flag\nmerge takes only head_skb's flag, and the inner switch that rebinds\nfrag_skb to list_skb on head_skb-frags exhaustion does not fold the\nnew frag_skb's flag into nskb.  Fold frag_skb's flag at both sites\nso segments drawing frags from frag_list members carry the marker.","modified":"2026-07-09T18:31:14.404637729Z","published":"2026-05-23T11:44:01.103Z","related":["SUSE-SU-2026:2111-1","SUSE-SU-2026:21834-1","SUSE-SU-2026:21841-1","SUSE-SU-2026:21845-1","SUSE-SU-2026:21860-1","SUSE-SU-2026:21876-1","SUSE-SU-2026:21877-1","SUSE-SU-2026:21916-1","SUSE-SU-2026:21919-1","SUSE-SU-2026:2202-1","SUSE-SU-2026:22108-1","SUSE-SU-2026:22137-1","SUSE-SU-2026:2215-1","SUSE-SU-2026:2216-1","SUSE-SU-2026:2217-1","SUSE-SU-2026:22276-1","SUSE-SU-2026:22277-1","SUSE-SU-2026:22278-1","SUSE-SU-2026:22279-1","SUSE-SU-2026:22280-1","SUSE-SU-2026:22281-1","SUSE-SU-2026:22282-1","SUSE-SU-2026:22283-1","SUSE-SU-2026:22288-1","SUSE-SU-2026:2238-1","SUSE-SU-2026:22383-1","SUSE-SU-2026:22384-1","SUSE-SU-2026:22385-1","SUSE-SU-2026:22386-1","SUSE-SU-2026:22387-1","SUSE-SU-2026:22388-1","SUSE-SU-2026:22389-1","SUSE-SU-2026:22390-1","SUSE-SU-2026:22391-1","SUSE-SU-2026:22396-1","SUSE-SU-2026:22397-1","SUSE-SU-2026:22398-1","SUSE-SU-2026:22399-1","SUSE-SU-2026:22400-1","SUSE-SU-2026:22401-1","SUSE-SU-2026:22402-1","SUSE-SU-2026:22403-1","SUSE-SU-2026:22404-1","SUSE-SU-2026:22405-1","SUSE-SU-2026:22406-1","SUSE-SU-2026:22407-1","SUSE-SU-2026:22408-1","SUSE-SU-2026:22409-1","SUSE-SU-2026:22410-1","SUSE-SU-2026:22411-1","SUSE-SU-2026:22412-1","SUSE-SU-2026:22413-1","SUSE-SU-2026:22414-1","SUSE-SU-2026:22415-1","SUSE-SU-2026:22416-1","SUSE-SU-2026:22417-1","SUSE-SU-2026:22418-1","SUSE-SU-2026:22419-1","SUSE-SU-2026:22420-1","SUSE-SU-2026:22421-1","SUSE-SU-2026:22425-1","SUSE-SU-2026:22426-1","SUSE-SU-2026:22427-1","SUSE-SU-2026:22428-1","SUSE-SU-2026:22433-1","SUSE-SU-2026:22458-1","SUSE-SU-2026:22461-1","SUSE-SU-2026:22462-1","SUSE-SU-2026:22463-1","SUSE-SU-2026:22464-1","SUSE-SU-2026:22465-1","SUSE-SU-2026:22466-1","SUSE-SU-2026:22467-1","SUSE-SU-2026:22468-1","SUSE-SU-2026:22469-1","SUSE-SU-2026:22470-1","SUSE-SU-2026:22471-1","SUSE-SU-2026:22472-1","SUSE-SU-2026:22473-1","SUSE-SU-2026:22474-1","SUSE-SU-2026:22475-1","SUSE-SU-2026:22476-1","SUSE-SU-2026:22478-1","SUSE-SU-2026:22479-1","SUSE-SU-2026:22480-1","SUSE-SU-2026:22481-1","SUSE-SU-2026:22482-1","SUSE-SU-2026:22483-1","SUSE-SU-2026:22484-1","SUSE-SU-2026:22485-1","SUSE-SU-2026:22486-1","SUSE-SU-2026:22487-1","SUSE-SU-2026:22488-1","SUSE-SU-2026:22489-1","SUSE-SU-2026:22490-1","SUSE-SU-2026:22491-1","SUSE-SU-2026:22507-1","SUSE-SU-2026:22508-1","SUSE-SU-2026:22509-1","SUSE-SU-2026:2310-1","SUSE-SU-2026:2450-1","SUSE-SU-2026:2494-1","SUSE-SU-2026:2496-1","SUSE-SU-2026:2500-1","SUSE-SU-2026:2503-1","SUSE-SU-2026:2511-1","SUSE-SU-2026:2518-1","SUSE-SU-2026:2520-1","SUSE-SU-2026:2532-1","SUSE-SU-2026:2549-1","SUSE-SU-2026:2553-1","SUSE-SU-2026:2559-1","SUSE-SU-2026:2567-1","SUSE-SU-2026:2571-1","SUSE-SU-2026:2588-1","SUSE-SU-2026:2592-1","SUSE-SU-2026:2594-1","SUSE-SU-2026:2601-1","SUSE-SU-2026:2603-1","SUSE-SU-2026:2607-1","SUSE-SU-2026:2608-1","SUSE-SU-2026:2610-1","SUSE-SU-2026:2630-1","SUSE-SU-2026:2658-1","openSUSE-SU-2026:10954-1","openSUSE-SU-2026:20826-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43503.json","cna_assigner":"Linux"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/12401fcfb01f53ccc63ab0a3246570fe8f3105ee"},{"type":"WEB","url":"https://git.kernel.org/stable/c/179f1852bdedc300e373e807cc102cd81feff196"},{"type":"WEB","url":"https://git.kernel.org/stable/c/48f6a5356a33dd78e7144ae1faef95ffc990aae0"},{"type":"WEB","url":"https://git.kernel.org/stable/c/989214c66884d70716d83dc1d0bf5e16287bf349"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9bc9d6d6967a2239aa57af2aa53554eddd640d20"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fbeab9555564a1b98e8582cd106dfe46c4606991"},{"type":"WEB","url":"https://git.kernel.org/stable/c/fc6eb39c55e97df2f94ad974b8a5bbcd019da2c8"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ff375cc75f9167168db38e0464a482d5fbc8d81d"},{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-43503.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19521"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19540"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19568"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19569"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19664"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19666"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19705"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19711"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:19875"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:20051"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:20054"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:20087"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RH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