Description

In the Linux kernel, the following vulnerability has been resolved: initramfs: avoid filename buffer overrun The initramfs filename field is defined in Documentation/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 \0 When extracting an initramfs cpio archive, the kernel's do_name() path handler assumes a zero-terminated path at @collected, passing it directly to filp_open() / init_mkdir() / init_mknod(). If a specially crafted cpio entry carries a non-zero-terminated filename and is followed by uninitialized memory, then a file may be created with trailing characters that represent the uninitialized memory. The ability to create an initramfs entry would imply already having full control of the system, so the buffer overrun shouldn't be considered a security vulnerability. Append the output of the following bash script to an existing initramfs and observe any created /initramfs_test_fname_overrunAA* path. E.g. ./reproducer.sh | gzip >> /myinitramfs It's easiest to observe non-zero uninitialized memory when the output is gzipped, 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 / pad magic="070701" ino=1 mode=$(( 0100777 )) uid=0 gid=0 nlink=1 mtime=1 filesize=0 devmajor=0 devminor=1 rdevmajor=0 rdevminor=0 csum=0 fname="initramfs_test_fname_overrun" namelen=$(( ${#fname} + 1 )) # plus one to account for terminator printf "%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 $fname termpadlen=$(( 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 the data segment, due to the explicit zero-termination of the symlink target. Fix filename buffer overrun by aborting the initramfs FSM if any cpio entry doesn't carry a zero-terminator at the expected (name_len - 1) offset.

Weaknesses 1

Affected Products 4

References 11

• git.kernel.org https://git.kernel.org/stable/c/1a423bbbeaf9e3e20c4686501efd9b661fe834db
  Patch
• git.kernel.org https://git.kernel.org/stable/c/49d01e736c3045319e030d1e75fb983011abaca7
  Patch
• git.kernel.org https://git.kernel.org/stable/c/6983b8ac787b3add5571cda563574932a59a99bb
• git.kernel.org https://git.kernel.org/stable/c/bb7ac96670ab1d8d681015f9d66e45dad579af4d
  Patch
• git.kernel.org https://git.kernel.org/stable/c/c509b1acbd867d9e09580fe059a924cb5825afb1
• git.kernel.org https://git.kernel.org/stable/c/d3df9f26cff97beaa5643e551031795d5d5cddbe
• git.kernel.org https://git.kernel.org/stable/c/e017671f534dd3f568db9e47b0583e853d2da9b5
  Patch
• git.kernel.org https://git.kernel.org/stable/c/f892ddcf9f645380c358e73653cb0900f6bc9eb8
• git.kernel.org https://git.kernel.org/stable/c/fb83b093f75806333b6f4ae29b158d2e0e3ec971
  Patch
• lists.debian.org https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html
• lists.debian.org https://lists.debian.org/debian-lts-announce/2025/03/msg00002.html

Remediation

• git.kernel.org https://git.kernel.org/stable/c/1a423bbbeaf9e3e20c4686501efd9b661fe834db
  Patch
• git.kernel.org https://git.kernel.org/stable/c/49d01e736c3045319e030d1e75fb983011abaca7
  Patch
• git.kernel.org https://git.kernel.org/stable/c/bb7ac96670ab1d8d681015f9d66e45dad579af4d
  Patch
• git.kernel.org https://git.kernel.org/stable/c/e017671f534dd3f568db9e47b0583e853d2da9b5
  Patch
• git.kernel.org https://git.kernel.org/stable/c/fb83b093f75806333b6f4ae29b158d2e0e3ec971
  Patch