{"id":"CVE-2026-98214","published":"2026-10-06T09:18:07.943","lastModified":"2026-10-06T09:18:07.943","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nselinux: recheck intermediate backing files on mprotect()\n\nmprotect() can be used to bypass the SELinux checks that mmap() performs\nagainst the intermediate layers of a stacked filesystem.\n\nmmap() checks every backing layer as the request descends through the\nstack.  mprotect() only has the lowest backing file in vma->vm_file, so it\nrechecks the top-level user and the lowest mounter, but skips the mounters\nof every layer in between.  With two nested overlayfs mounts and a policy\ndenying mounter_t -> middle_file_t:file { execute }, a direct\nmmap(PROT_EXEC) is denied:\n\n  avc:  denied  { execute } for  pid=71 comm=\"nested_exec\"\n    path=\"/payload\" dev=\"overlay\" ino=9\n    scontext=user_u:base_r:mounter_t\n    tcontext=user_u:object_r:middle_file_t tclass=file permissive=0\n\nwhile mmap(PROT_NONE) followed by mprotect(PROT_EXEC) succeeds.\n\nPreserve each intermediate path, mounter SID and file-description SID in\nthe backing-file security blob, copying the saved entries when another\nbacking layer is opened.  Allocate the array only for nested backing files,\nand release it and the path references in the backing_file_free hook.\n\nDuring mprotect(), recheck fd { use } and the requested inode permissions\nfor every saved mounter, and include the intermediate layers in the execmod\nchecks.  Policy for nested stacking may then need to grant intermediate\nmounters what a direct mmap() already requires, and execmod on intermediate\nlabels for binaries using text relocations.\n\nTested on arm64 QEMU with a small BusyBox initramfs and a purpose-built\nSELinux policy, on a mainline tree containing\ncommit f2381b546e7e (\"fs: fix user path of nested backing files\").\n\n[PM: subject tweak]","cvssScore":null,"cvssSeverity":null,"cvssVector":null,"cwes":[],"vendors":[],"products":[],"references":[{"url":"https://git.kernel.org/stable/c/4d50ebe5a27724e020747ffd61a051dec67cb8ec","tags":[]},{"url":"https://git.kernel.org/stable/c/78fc54b934bfb2c18aad8154c7302067146946f9","tags":[]},{"url":"https://git.kernel.org/stable/c/89376fbfdcc1a728e1775f98752cdd90b0930a00","tags":[]},{"url":"https://git.kernel.org/stable/c/c2bbb905af2293549651b614a52ad91e0b462b60","tags":[]},{"url":"https://git.kernel.org/stable/c/d127c7e1f3e1231d8ac8b2738e3f00bea12afe74","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}