{"cve":"CVE-2021-47656","nvd":{"published":"2025-02-26T06:37:07.360","modified":"2026-08-04T10:17:12.300","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\njffs2: fix use-after-free in jffs2_clear_xattr_subsystem\n\nWhen we mount a jffs2 image, assume that the first few blocks of\nthe image are normal and contain at least one xattr-related inode,\nbut the next block is abnormal. As a result, an error is returned\nin jffs2_scan_eraseblock(). jffs2_clear_xattr_subsystem() is then\ncalled in jffs2_build_filesystem() and then again in\njffs2_do_fill_super().\n\nFinally we can observe the following report:\n ==================================================================\n BUG: KASAN: use-after-free in jffs2_clear_xattr_subsystem+0x95/0x6ac\n Read of size 8 at addr ffff8881243384e0 by task mount/719\n\n Call Trace:\n  dump_stack+0x115/0x16b\n  jffs2_clear_xattr_subsystem+0x95/0x6ac\n  jffs2_do_fill_super+0x84f/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n  mtd_get_sb+0x254/0x400\n  mtd_get_sb_by_nr+0x4f/0xd0\n  get_tree_mtd+0x498/0x840\n  jffs2_get_tree+0x25/0x30\n  vfs_get_tree+0x8d/0x2e0\n  path_mount+0x50f/0x1e50\n  do_mount+0x107/0x130\n  __se_sys_mount+0x1c5/0x2f0\n  __x64_sys_mount+0xc7/0x160\n  do_syscall_64+0x45/0x70\n  entry_SYSCALL_64_after_hwframe+0x44/0xa9\n\n Allocated by task 719:\n  kasan_save_stack+0x23/0x60\n  __kasan_kmalloc.constprop.0+0x10b/0x120\n  kasan_slab_alloc+0x12/0x20\n  kmem_cache_alloc+0x1c0/0x870\n  jffs2_alloc_xattr_ref+0x2f/0xa0\n  jffs2_scan_medium.cold+0x3713/0x4794\n  jffs2_do_mount_fs.cold+0xa7/0x2253\n  jffs2_do_fill_super+0x383/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n Freed by task 719:\n  kmem_cache_free+0xcc/0x7b0\n  jffs2_free_xattr_ref+0x78/0x98\n  jffs2_clear_xattr_subsystem+0xa1/0x6ac\n  jffs2_do_mount_fs.cold+0x5e6/0x2253\n  jffs2_do_fill_super+0x383/0xc30\n  jffs2_fill_super+0x2ea/0x4c0\n [...]\n\n The buggy address belongs to the object at ffff8881243384b8\n  which belongs to the cache jffs2_xattr_ref of size 48\n The buggy address is located 40 bytes inside of\n  48-byte region [ffff8881243384b8, ffff8881243384e8)\n [...]\n ==================================================================\n\nThe triggering of the BUG is shown in the following stack:\n-----------------------------------------------------------\njffs2_fill_super\n  jffs2_do_fill_super\n    jffs2_do_mount_fs\n      jffs2_build_filesystem\n        jffs2_scan_medium\n          jffs2_scan_eraseblock        <--- ERROR\n        jffs2_clear_xattr_subsystem    <--- free\n    jffs2_clear_xattr_subsystem        <--- free again\n-----------------------------------------------------------\n\nAn error is returned in jffs2_do_mount_fs(). If the error is returned\nby jffs2_sum_init(), the jffs2_clear_xattr_subsystem() does not need to\nbe executed. If the error is returned by jffs2_build_filesystem(), the\njffs2_clear_xattr_subsystem() also does not need to be executed again.\nSo move jffs2_clear_xattr_subsystem() from 'out_inohash' to 'out_root'\nto fix this UAF problem.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","score":7.8},"cwes":["CWE-416"],"references":["https://git.kernel.org/stable/c/22327bd7988f21de3a53c1373f3b81542bfe1f44","https://git.kernel.org/stable/c/30bf7244acf32f19cb722c39f7bc1c2a9f300422","https://git.kernel.org/stable/c/3bd2454162ec6bbb5503233c804fce6e4b6dcec5","https://git.kernel.org/stable/c/4c7c44ee1650677fbe89d86edbad9497b7679b5c","https://git.kernel.org/stable/c/7a75740206af5f17e9f3efa384211cba70213da1"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T21:59:48.811064707+00:00"},"epss":{"cve":"CVE-2021-47656","score":0.00258,"percentile":0.17567,"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."]}