selinux: recheck intermediate backing files on mprotect()
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 6.6.158, 6.12.112, 6.18.54, 7.1, 7.2.8
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
In the Linux kernel, the following vulnerability has been resolved: selinux: recheck intermediate backing files on mprotect() mprotect() can be used to bypass the SELinux checks that mmap() performs against the intermediate layers of a stacked filesystem. mmap() checks every backing layer as the request descends through the stack. mprotect() only has the lowest backing file in vma->vm_file, so it rechecks the top-level user and the lowest mounter, but skips the mounters of every layer in between. With two nested overlayfs mounts and a policy denying mounter_t -> middle_file_t:file { execute }, a direct mmap(PROT_EXEC) is denied: avc: denied { execute } for pid=71 comm="nested_exec" path="/payload" dev="overlay" ino=9 scontext=user_u:base_r:mounter_t tcontext=user_u:object_r:middle_file_t tclass=file permissive=0 while mmap(PROT_NONE) followed by mprotect(PROT_EXEC) succeeds. Preserve each intermediate path, mounter SID and file-description SID in the backing-file security blob, copying the saved entries when another backing layer is opened. Allocate the array only for nested backing files, and release it and the path references in the backing_file_free hook. During mprotect(), recheck fd { use } and the requested inode permissions for every saved mounter, and include the intermediate layers in the execmod checks. Policy for nested stacking may then need to grant intermediate mounters what a direct mmap() already requires, and execmod on intermediate labels for binaries using text relocations. Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built SELinux policy, on a mainline tree containing commit f2381b546e7e ("fs: fix user path of nested backing files"). [PM: subject tweak]
Timeline
- CVE published
- Record last updated
Affected versions
- Linux Linux
From bc6c380c1159de52a252ed11f19a42c47f60a735 · fixed in 4d50ebe5a27724e020747ffd61a051dec67cb8ec; From 8bacd09f12c27710228562e4d13163e58c5f4a45 · fixed in 89376fbfdcc1a728e1775f98752cdd90b0930a00; From d844702198395d3f80222777030f69db6be6b709 · fixed in d127c7e1f3e1231d8ac8b2738e3f00bea12afe74; From 82544d36b1729153c8aeb179e84750f0c085d3b1 · fixed in c2bbb905af2293549651b614a52ad91e0b462b60; From 82544d36b1729153c8aeb179e84750f0c085d3b1 · fixed in 78fc54b934bfb2c18aad8154c7302067146946f9; From 6.6.144 · fixed in 6.6.158; From 6.12.95 · fixed in 6.12.112; From 6.18.38 · fixed in 6.18.54; From 7.0.4 · fixed in 7.1
- Linux Linux
7.1
- KernelLinux
fixed in 6.6.158; From 6.7.0 · fixed in 6.12.112; From 6.13.0 · fixed in 6.18.54; From 6.19.0 · fixed in 7.2.8