{"cve":"CVE-2026-53040","nvd":{"published":"2026-06-24T17:17:15.687","modified":"2026-07-14T19:33:51.517","status":"Analyzed","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nocfs2: validate bg_bits during freefrag scan\n\n[BUG]\nA crafted filesystem can trigger an out-of-bounds bitmap walk when\nOCFS2_IOC_INFO is issued with OCFS2_INFO_FL_NON_COHERENT.\n\nBUG: KASAN: use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline]\nBUG: KASAN: use-after-free in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]\nBUG: KASAN: use-after-free in test_bit_le include/asm-generic/bitops/le.h:21 [inline]\nBUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline]\nBUG: KASAN: use-after-free in ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline]\nBUG: KASAN: use-after-free in ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline]\nBUG: KASAN: use-after-free in ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754\nRead of size 8 at addr ffff888031bce000 by task syz.0.636/1435\nCall Trace:\n __dump_stack lib/dump_stack.c:94 [inline]\n dump_stack_lvl+0xbe/0x130 lib/dump_stack.c:120\n print_address_description mm/kasan/report.c:378 [inline]\n print_report+0xd1/0x650 mm/kasan/report.c:482\n kasan_report+0xfb/0x140 mm/kasan/report.c:595\n check_region_inline mm/kasan/generic.c:186 [inline]\n kasan_check_range+0x11c/0x200 mm/kasan/generic.c:200\n __kasan_check_read+0x11/0x20 mm/kasan/shadow.c:31\n instrument_atomic_read include/linux/instrumented.h:68 [inline]\n _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]\n test_bit_le include/asm-generic/bitops/le.h:21 [inline]\n ocfs2_info_freefrag_scan_chain fs/ocfs2/ioctl.c:495 [inline]\n ocfs2_info_freefrag_scan_bitmap fs/ocfs2/ioctl.c:588 [inline]\n ocfs2_info_handle_freefrag fs/ocfs2/ioctl.c:662 [inline]\n ocfs2_info_handle_request+0x1c66/0x3370 fs/ocfs2/ioctl.c:754\n ocfs2_info_handle+0x18d/0x2a0 fs/ocfs2/ioctl.c:828\n ocfs2_ioctl+0x632/0x6e0 fs/ocfs2/ioctl.c:913\n vfs_ioctl fs/ioctl.c:51 [inline]\n __do_sys_ioctl fs/ioctl.c:597 [inline]\n __se_sys_ioctl fs/ioctl.c:583 [inline]\n __x64_sys_ioctl+0x197/0x1e0 fs/ioctl.c:583\n ...\n\n[CAUSE]\nocfs2_info_freefrag_scan_chain() uses on-disk bg_bits directly as the\nbitmap scan limit. The coherent path reads group descriptors through\nocfs2_read_group_descriptor(), which validates the descriptor before\nuse. The non-coherent path uses ocfs2_read_blocks_sync() instead and\nskips that validation, so an impossible bg_bits value can drive the\nbitmap walk past the end of the block.\n\n[FIX]\nCompute the bitmap capacity from the filesystem format with\nocfs2_group_bitmap_size(), report descriptors whose bg_bits exceeds\nthat limit, and clamp the scan to the computed capacity. This keeps the\nfreefrag report going while avoiding reads beyond the buffer.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","score":7.1},"cwes":["CWE-416"],"references":["https://git.kernel.org/stable/c/05d0cbea41167b6b061c6ba5b70ee5a9a7a24c9e","https://git.kernel.org/stable/c/0998674eec138c55e9e349b9cbd9dbc5129a9cc8","https://git.kernel.org/stable/c/3e167e230d19cd273108bab2e4c61800fc335ae8","https://git.kernel.org/stable/c/4c2d62ddde8928db12f4608950b67a20e67deab2","https://git.kernel.org/stable/c/8f687eeed3da3012152b0f9473f578869de0cd7b"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:41:17.107060303+00:00"},"epss":{"cve":"CVE-2026-53040","score":0.00122,"percentile":0.01968,"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."]}