{"cve":"CVE-2021-47544","nvd":{"published":"2024-05-24T15:15:18.983","modified":"2026-08-04T10:17:08.120","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\ntcp: fix page frag corruption on page fault\n\nSteffen reported a TCP stream corruption for HTTP requests\nserved by the apache web-server using a cifs mount-point\nand memory mapping the relevant file.\n\nThe root cause is quite similar to the one addressed by\ncommit 20eb4f29b602 (\"net: fix sk_page_frag() recursion from\nmemory reclaim\"). Here the nested access to the task page frag\nis caused by a page fault on the (mmapped) user-space memory\nbuffer coming from the cifs file.\n\nThe page fault handler performs an smb transaction on a different\nsocket, inside the same process context. Since sk->sk_allaction\nfor such socket does not prevent the usage for the task_frag,\nthe nested allocation modify \"under the hood\" the page frag\nin use by the outer sendmsg call, corrupting the stream.\n\nThe overall relevant stack trace looks like the following:\n\nhttpd 78268 [001] 3461630.850950:      probe:tcp_sendmsg_locked:\n        ffffffff91461d91 tcp_sendmsg_locked+0x1\n        ffffffff91462b57 tcp_sendmsg+0x27\n        ffffffff9139814e sock_sendmsg+0x3e\n        ffffffffc06dfe1d smb_send_kvec+0x28\n        [...]\n        ffffffffc06cfaf8 cifs_readpages+0x213\n        ffffffff90e83c4b read_pages+0x6b\n        ffffffff90e83f31 __do_page_cache_readahead+0x1c1\n        ffffffff90e79e98 filemap_fault+0x788\n        ffffffff90eb0458 __do_fault+0x38\n        ffffffff90eb5280 do_fault+0x1a0\n        ffffffff90eb7c84 __handle_mm_fault+0x4d4\n        ffffffff90eb8093 handle_mm_fault+0xc3\n        ffffffff90c74f6d __do_page_fault+0x1ed\n        ffffffff90c75277 do_page_fault+0x37\n        ffffffff9160111e page_fault+0x1e\n        ffffffff9109e7b5 copyin+0x25\n        ffffffff9109eb40 _copy_from_iter_full+0xe0\n        ffffffff91462370 tcp_sendmsg_locked+0x5e0\n        ffffffff91462370 tcp_sendmsg_locked+0x5e0\n        ffffffff91462b57 tcp_sendmsg+0x27\n        ffffffff9139815c sock_sendmsg+0x4c\n        ffffffff913981f7 sock_write_iter+0x97\n        ffffffff90f2cc56 do_iter_readv_writev+0x156\n        ffffffff90f2dff0 do_iter_write+0x80\n        ffffffff90f2e1c3 vfs_writev+0xa3\n        ffffffff90f2e27c do_writev+0x5c\n        ffffffff90c042bb do_syscall_64+0x5b\n        ffffffff916000ad entry_SYSCALL_64_after_hwframe+0x65\n\nThe cifs filesystem rightfully sets sk_allocations to GFP_NOFS,\nwe can avoid the nesting using the sk page frag for allocation\nlacking the __GFP_FS flag. Do not define an additional mm-helper\nfor that, as this is strictly tied to the sk page frag usage.\n\nv1 -> v2:\n - use a stricted sk_page_frag() check instead of reordering the\n   code (Eric)","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N","score":5.9},"cwes":[],"references":["https://git.kernel.org/stable/c/5a9afcd827cafe14a95c9fcbded2c2d104f18dfc","https://git.kernel.org/stable/c/c6f340a331fb72e5ac23a083de9c780e132ca3ae","https://git.kernel.org/stable/c/dacb5d8875cc6cd3a553363b4d6f06760fcbe70c","https://git.kernel.org/stable/c/5a9afcd827cafe14a95c9fcbded2c2d104f18dfc","https://git.kernel.org/stable/c/c6f340a331fb72e5ac23a083de9c780e132ca3ae"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T21:50:30.954589733+00:00"},"epss":{"cve":"CVE-2021-47544","score":0.00863,"percentile":0.58608,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}