CVE-2026-72385: tracing/fprobe: Fix NULL pointer dereference in fprobe_fgraph_entry()

CVE-2026-72385: tracing/fprobe: Fix NULL pointer dereference in fprobe_fgraph_entry()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

tracing/fprobe: Fix NULL pointer dereference in fprobe_fgraph_entry()

fprobe_fgraph_entry() sizes a shadow-stack reservation in one walk of
the per-ip fprobe list and fills it in a second walk, both under
rcu_read_lock() only. A fprobe registered on an already-live ip can
become visible between the two walks, so the fill walk processes an
exit_handler the sizing walk did not count and used runs past
reserved_words. If the sizing walk counted nothing, fgraph_data is NULL
and the first write_fprobe_header() faults:

  Oops: general protection fault, probably for non-canonical address ...
  KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
  RIP: 0010:fprobe_fgraph_entry+0xa38/0xf10 kernel/trace/fprobe.c:167
  Call Trace:
   <TASK>
   function_graph_enter_regs+0x44c/0xa10 kernel/trace/fgraph.c:677
   ftrace_graph_func+0xc5/0x140 arch/x86/kernel/ftrace.c:671
   __kernel_text_address+0x9/0x40 kernel/extable.c:78
   arch_stack_walk+0x117/0x170 arch/x86/kernel/stacktrace.c:26
   kmem_cache_free+0x188/0x580 mm/slub.c:6378
   tcp_data_queue+0x18d/0x6550 net/ipv4/tcp_input.c:5590
   [...]
   </TASK>

The list cannot be frozen across the two walks, so skip a node that does
not fit the reservation and count it as missed.

The Linux kernel CVE team has assigned CVE-2026-72385 to this issue.


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

	Issue introduced in 6.14 with commit 4346ba1604093305a287e08eb465a9c15ba05b80 and fixed in 6.18.40 with commit 62988204162fc382cfc7d9a185d40a751261e3a3
	Issue introduced in 6.14 with commit 4346ba1604093305a287e08eb465a9c15ba05b80 and fixed in 7.1.5 with commit d655cca1c6e67eb081214d37eb231a869ead2f97
	Issue introduced in 6.14 with commit 4346ba1604093305a287e08eb465a9c15ba05b80 and fixed in 7.2-rc2 with commit 367c49d6e283c17b56a31e7a8d964a079244264c

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-2026-72385
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/trace/fprobe.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/62988204162fc382cfc7d9a185d40a751261e3a3
	https://git.kernel.org/stable/c/d655cca1c6e67eb081214d37eb231a869ead2f97
	https://git.kernel.org/stable/c/367c49d6e283c17b56a31e7a8d964a079244264c