CVE-2026-74477: uprobes: Fix NULL pointer dereference in hprobe_expire()

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

uprobes: Fix NULL pointer dereference in hprobe_expire()

Forking a task that has a pending uretprobe can oops the kernel with a
NULL pointer dereference in the clone() path:

  BUG: kernel NULL pointer dereference, address: 0000000000000018
  Oops: 0002 [#1] SMP NOPTI
  RIP: 0010:hprobe_expire
  CR2: 0000000000000018
  Call Trace:
   uprobe_copy_process
   copy_process
   kernel_clone
   __x64_sys_clone
   do_syscall_64
   entry_SYSCALL_64_after_hwframe

This was found on real hosts on Meta fleet.

I've got the impression that this is what is happening:

  CPU 1                          CPU 2 (traced task)
  -----                          -------------------
                                 hit uprobe, prepare_uretprobe():
                                   hprobe LEASED, refcount >= 1
  uprobe_unregister()
    put_uprobe(): refcount -> 0
                                 fork() -> dup_utask()
                                   hprobe_expire(hprobe, true)
                                     try_get_uprobe() -> NULL
                                     get_uprobe(NULL)   <-- Oops

Only take the extra reference when the uprobe is non-NULL; a NULL means
it is gone and is the correct value to return.

The Linux kernel CVE team has assigned CVE-2026-74477 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.13 with commit dd1a7567784e2b1f80258be04f57bcfa82c997eb and fixed in 6.18.44 with commit 3bd35a5e272a1b7a3fb43acad9bdc599281b13fa
	Issue introduced in 6.13 with commit dd1a7567784e2b1f80258be04f57bcfa82c997eb and fixed in 7.1.8 with commit 06c275a6c0a953ef1d763d11a6891fcc69ae2ac0
	Issue introduced in 6.13 with commit dd1a7567784e2b1f80258be04f57bcfa82c997eb and fixed in 7.2-rc6 with commit cc679d7a6303e84d769f2afcde1fc51c51f127cd

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74477
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/events/uprobes.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/3bd35a5e272a1b7a3fb43acad9bdc599281b13fa
	https://git.kernel.org/stable/c/06c275a6c0a953ef1d763d11a6891fcc69ae2ac0
	https://git.kernel.org/stable/c/cc679d7a6303e84d769f2afcde1fc51c51f127cd