{"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":"2026-06-04T09:14:20.695388770Z","published":"2026-05-23T11:44:01.103Z","related":["SUSE-SU-2026:2111-1","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-2026:2215-1","SUSE-SU-2026:2216-1","SUSE-SU-2026:2217-1","SUSE-SU-2026:2238-1","openSUSE-SU-2026:20826-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43503.json"},"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":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43503.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-43503"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"cef401de7be8c4e155c6746bfccf721a4fa5fab9"},{"fixed":"fbeab9555564a1b98e8582cd106dfe46c4606991"},{"fixed":"179f1852bdedc300e373e807cc102cd81feff196"},{"fixed":"12401fcfb01f53ccc63ab0a3246570fe8f3105ee"},{"fixed":"989214c66884d70716d83dc1d0bf5e16287bf349"},{"fixed":"fc6eb39c55e97df2f94ad974b8a5bbcd019da2c8"},{"fixed":"ff375cc75f9167168db38e0464a482d5fbc8d81d"},{"fixed":"9bc9d6d6967a2239aa57af2aa53554eddd640d20"},{"fixed":"48f6a5356a33dd78e7144ae1faef95ffc990aae0"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-43503.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.9.0"},{"fixed":"5.10.257"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.208"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.174"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.141"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.91"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.33"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.0.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-43503.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H"}]}