CVE-2024-53142: initramfs: avoid filename buffer overrun

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 cpiofile := ALGN(4) + cpioheader + filename + "\0" + ALGN(4) + data ... 55 ============= ================== ========================= 56 Field name Field size Meaning 57 ============= ================== ========================= ... 70 cnamesize 8 bytes Length of filename, including final \0

When extracting an initramfs cpio archive, the kernel's doname() path handler assumes a zero-terminated path at @collected, passing it directly to filpopen() / initmkdir() / initmknod().

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 /initramfstestfnameoverrunAA 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 @outbuf in gunzip(), rather than the initrdstart+initrdsize block.

---- reproducer.sh ---- nilchar="A" # change to "\0" to properly zero terminate / pad magic="070701" ino=1 mode=$(( 0100777 )) uid=0 gid=0 nlink=1 mtime=1 filesize=0 devmajor=0 devminor=1 rdevmajor=0 rdevminor=0 csum=0 fname="initramfstestfnameoverrun" namelen=$(( ${#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 dosymlink() 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 (namelen - 1) offset.

— NVD

This CVE was automatically created from a reference found in an email or other text. If you are reading this, then this CVE entry is probably erroneous, since this text should be replaced by the official CVE description automatically.

— Launchpad