CVE-2026-74382: net/sched: cls_bpf: prevent unbounded recursion in offload rollback

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

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

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

net/sched: cls_bpf: prevent unbounded recursion in offload rollback

Quan Sun reported [1] a stack overflow in cls_bpf_offload_cmd().

Reproducer on netdevsim: add a skip_sw cls_bpf filter, set the
bpf_tc_accept debugfs knob to 0, then `tc filter replace`. The replace
calls tc_setup_cb_replace() which fails. cls_bpf_offload_cmd() then
swaps prog/oldprog and recursively calls itself to roll back. But
bpf_tc_accept=0 makes the rollback fail too, which triggers yet another
rollback frame with the same arguments, and so on until the stack is
exhausted.

bpf_tc_accept is just a convenient knob for the reproducer. Any driver
whose tc_setup_cb_replace() fails twice in a row can hit the same loop,
so this is not a netdevsim-only issue.

Two ways to fix it:

  1) Have the rollback call tc_setup_cb_add() on oldprog instead of
     re-entering cls_bpf_offload_cmd().
  2) Mark the rollback frame with a flag and skip a second-level
     rollback from inside it.

Go with (2). It is the smaller change and keeps the original behaviour:
the rollback still goes through tc_setup_cb_replace(), so the driver
gets one real chance to restore its state. If that attempt also fails,
we just return the original error instead of recursing.

[1]: https://lore.kernel.org/bpf/[email protected]/T/#u

The Linux kernel CVE team has assigned CVE-2026-74382 to this issue.


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

	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 5.10.261 with commit a018f208ab7512380bd4cf670064d48cba00a1b1
	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 5.15.212 with commit 33373e1f378a501bc51aa73312f74295c84e3101
	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 6.1.178 with commit e2d3b7bab3748c811dc5750ce9a8d62bc7f90ed7
	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 6.6.145 with commit 4a76953c3ed043797e81529b9395e9ca6f4c7609
	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 6.12.97 with commit 1387f252a242a51bfbb6eace29c8f8db21b457da
	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 6.18.40 with commit 10753da2d659dd425a6e620f47f86852d604f67f
	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 7.1.5 with commit 3fa6fb5d771c992ebedbfa7331c6bcc6f33f89b7
	Issue introduced in 4.15 with commit 102740bd9436a3a6ba129af3a48271d794009fa5 and fixed in 7.2-rc1 with commit 27db54b90bcc7c37867fe664107fa25ea6a116e4

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-2026-74382
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:
	net/sched/cls_bpf.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/a018f208ab7512380bd4cf670064d48cba00a1b1
	https://git.kernel.org/stable/c/33373e1f378a501bc51aa73312f74295c84e3101
	https://git.kernel.org/stable/c/e2d3b7bab3748c811dc5750ce9a8d62bc7f90ed7
	https://git.kernel.org/stable/c/4a76953c3ed043797e81529b9395e9ca6f4c7609
	https://git.kernel.org/stable/c/1387f252a242a51bfbb6eace29c8f8db21b457da
	https://git.kernel.org/stable/c/10753da2d659dd425a6e620f47f86852d604f67f
	https://git.kernel.org/stable/c/3fa6fb5d771c992ebedbfa7331c6bcc6f33f89b7
	https://git.kernel.org/stable/c/27db54b90bcc7c37867fe664107fa25ea6a116e4