Entreprise française de cybersécurité depuis 2004
☎ 03 60 47 09 81 - info@securiteinfo.com
☎ 03 60 47 09 81 - info@securiteinfo.com
In the Linux kernel, the following vulnerability has been resolved:initramfs: avoid filename buffer overrunThe initramfs filename field is defined inDocumentation/driver-api/early-userspace/buffer-format.rst as: 37 cpio_file := ALGN(4) + cpio_header + filename + "\0" + ALGN(4) + data... 55 ============= ================== ========================= 56 Field name Field size Meaning 57 ============= ================== =========================... 70 c_namesize 8 bytes Length of filename, including final \0When extracting an initramfs cpio archive, the kernel's do_name() pathhandler assumes a zero-terminated path at @collected, passing itdirectly to filp_open() / init_mkdir() / init_mknod().If a specially crafted cpio entry carries a non-zero-terminated filenameand is followed by uninitialized memory, then a file may be created withtrailing characters that represent the uninitialized memory. The abilityto create an initramfs entry would imply already having full control ofthe system, so the buffer overrun shouldn't be considered a securityvulnerability.Append the output of the following bash script to an existing initramfsand observe any created /initramfs_test_fname_overrunAA* path. E.g. ./reproducer.sh | gzip >> /myinitramfsIt's easiest to observe non-zero uninitialized memory when the output isgzipped, as it'll overflow the heap allocated @out_buf in __gunzip(),rather than the initrd_start+initrd_size block.---- reproducer.sh ----nilchar="A" # change to "\0" to properly zero terminate / padmagic="070701"ino=1mode=$(( 0100777 ))uid=0gid=0nlink=1mtime=1filesize=0devmajor=0devminor=1rdevmajor=0rdevminor=0csum=0fname="initramfs_test_fname_overrun"namelen=$(( ${#fname} + 1 )) # plus one to account for terminatorprintf "%s%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%s" \ $magic $ino $mode $uid $gid $nlink $mtime $filesize \ $devmajor $devminor $rdevmajor $rdevminor $namelen $csum $fnametermpadlen=$(( 1 + ((4 - ((110 + $namelen) & 3)) % 4) ))printf "%.s${nilchar}" $(seq 1 $termpadlen)---- reproducer.sh ----Symlink filename fields handled in do_symlink() won't overrun past thedata segment, due to the explicit zero-termination of the symlinktarget.Fix filename buffer overrun by aborting the initramfs FSM if any cpioentry doesn't carry a zero-terminator at the expected (name_len - 1)offset.
No PoCs from references.
- https://github.com/w4zu/Debian_security