{"id":"CVE-2025-39879","revision":"cd3c37797b9747c497c5771f2fc684fe","records":[{"revision":"cd3c37797b9747c497c5771f2fc684fe","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2025-39879","aliases":[],"title":"ceph: always call ceph_shift_unused_folios_left()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nceph: always call ceph_shift_unused_folios_left()\n\nThe function ceph_process_folio_batch() sets folio_batch entries to\nNULL, which is an illegal state. Before folio_batch_release() crashes\ndue to this API violation, the function ceph_shift_unused_folios_left()\nis supposed to remove those NULLs from the array.\n\nHowever, since commit ce80b76dd327 (\"ceph: introduce\nceph_process_folio_batch() method\"), this shifting doesn't happen\nanymore because the \"for\" loop got moved to ceph_process_folio_batch(),\nand now the `i` variable that remains in ceph_writepages_start()\ndoesn't get incremented anymore, making the shifting effectively\nunreachable much of the time.\n\nLater, commit 1551ec61dc55 (\"ceph: introduce ceph_submit_write()\nmethod\") added more preconditions for doing the shift, replacing the\n`i` check (with something that is still just as broken):\n\n- if ceph_process_folio_batch() fails, shifting never happens\n\n- if ceph_move_dirty_page_in_page_array() was never called (because\n ceph_process_folio_batch() has returned early for some of various\n reasons), shifting never happens\n\n- if `processed_in_fbatch` is zero (because ceph_process_folio_batch()\n has returned early for some of the reasons mentioned above or\n because ceph_move_dirty_page_in_page_array() has failed), shifting\n never happens\n\nSince those two commits, any problem in ceph_process_folio_batch()\ncould crash the kernel, e.g. this way:\n\n BUG: kernel NULL pointer dereference, address: 0000000000000034\n #PF: supervisor write access in kernel mode\n #PF: error_code(0x0002) - not-present page\n PGD 0 P4D 0\n Oops: Oops: 0002 [#1] SMP NOPTI\n CPU: 172 UID: 0 PID: 2342707 Comm: kworker/u778:8 Not tainted 6.15.10-cm4all1-es #714 NONE\n Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.10 12/08/2023\n Workqueue: writeback wb_workfn (flush-ceph-1)\n RIP: 0010:folios_put_refs+0x85/0x140\n Code: 83 c5 01 39 e8 7e 76 48 63 c5 49 8b 5c c4 08 b8 01 00 00 00 4d 85 ed 74 05 41 8b 44 ad 00 48 8b 15 b0 >\n RSP: 0018:ffffb880af8db778 EFLAGS: 00010207\n RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000003\n RDX: ffffe377cc3b0000 RSI: 0000000000000000 RDI: ffffb880af8db8c0\n RBP: 0000000000000000 R08: 000000000000007d R09: 000000000102b86f\n R10: 0000000000000001 R11: 00000000000000ac R12: ffffb880af8db8c0\n R13: 0000000000000000 R14: 0000000000000000 R15: ffff9bd262c97000\n FS: 0000000000000000(0000) GS:ffff9c8efc303000(0000) knlGS:0000000000000000\n CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\n CR2: 0000000000000034 CR3: 0000000160958004 CR4: 0000000000770ef0\n PKRU: 55555554\n Call Trace:\n \n ceph_writepages_start+0xeb9/0x1410\n\nThe crash can be reproduced easily by changing the\nceph_check_page_before_write() return value to `-E2BIG`.\n\n(Interestingly, the crash happens only if `huge_zero_folio` has\nalready been allocated; without `huge_zero_folio`,\nis_huge_zero_folio(NULL) returns true and folios_put_refs() skips NULL\nentries instead of dereferencing them. That makes reproducing the bug\nsomewhat unreliable. See\nhttps://lore.kernel.org/20250826231626.218675-1-max.kellermann@ionos.com\nfor a discussion of this detail.)\n\nMy suggestion is to move the ceph_shift_unused_folios_left() to right\nafter ceph_process_folio_batch() to ensure it always gets called to\nfix up the illegal folio_batch state.","state":0,"publishedAt":"2025-09-23T06:00:49.377+00:00","modifiedAt":"2026-10-21T12:37:32.477+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"unaffected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/ceph/addr.c\"\n ],\n \"versions\": [\n {\n \"version\": \"0f2b2b7cacf888229cec19126e6791b11fb35f32\",\n \"lessThan\": \"523214f0afa1b3d0e696917bc5a4d0737718e3d7\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"ce80b76dd32764cc914975777e058d4fae4f0ea0\",\n \"lessThan\": \"289b6615cf553d98509a9b273195d9936da1cfb2\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n },\n {\n \"version\": \"ce80b76dd32764cc914975777e058d4fae4f0ea0\",\n \"lessThan\": \"cce7c15faaac79b532a07ed6ab8332280ad83762\",\n \"status\": \"affected\",\n \"versionType\": \"git\"\n }\n ]\n }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n \"product\": \"Linux\",\n \"vendor\": \"Linux\",\n \"defaultStatus\": \"affected\",\n \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n \"programFiles\": [\n \"fs/ceph/addr.c\"\n ],\n \"versions\": [\n {\n \"version\": \"6.15\",\n \"status\": \"affected\"\n },\n {\n \"version\": \"0\",\n \"lessThan\": \"6.15\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.16.8\",\n \"lessThanOrEqual\": \"6.16.*\",\n \"status\": \"unaffected\",\n \"versionType\": \"semver\"\n },\n {\n \"version\": \"6.17\",\n \"lessThanOrEqual\": \"*\",\n \"status\": \"unaffected\",\n \"versionType\": \"original_commit_for_fix\"\n }\n ]\n }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/523214f0afa1b3d0e696917bc5a4d0737718e3d7","https://git.kernel.org/stable/c/289b6615cf553d98509a9b273195d9936da1cfb2","https://git.kernel.org/stable/c/cce7c15faaac79b532a07ed6ab8332280ad83762"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2025-39879","license":"CVE Program Terms of Use","key":"cve-program:CVE-2025-39879","identifiers":["CVE-2025-39879"]},"retained":false,"historicalAffected":[]}],"coverage":[]}