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Victor Nogueira 923a276c74 net/sched: Abort __tc_modify_qdisc if parent class does not exist
[ Upstream commit ffdde7bf5a439aaa1955ebd581f5c64ab1533963 ]

Lion's patch [1] revealed an ancient bug in the qdisc API.
Whenever a user creates/modifies a qdisc specifying as a parent another
qdisc, the qdisc API will, during grafting, detect that the user is
not trying to attach to a class and reject. However grafting is
performed after qdisc_create (and thus the qdiscs' init callback) is
executed. In qdiscs that eventually call qdisc_tree_reduce_backlog
during init or change (such as fq, hhf, choke, etc), an issue
arises. For example, executing the following commands:

sudo tc qdisc add dev lo root handle a: htb default 2
sudo tc qdisc add dev lo parent a: handle beef fq

Qdiscs such as fq, hhf, choke, etc unconditionally invoke
qdisc_tree_reduce_backlog() in their control path init() or change() which
then causes a failure to find the child class; however, that does not stop
the unconditional invocation of the assumed child qdisc's qlen_notify with
a null class. All these qdiscs make the assumption that class is non-null.

The solution is ensure that qdisc_leaf() which looks up the parent
class, and is invoked prior to qdisc_create(), should return failure on
not finding the class.
In this patch, we leverage qdisc_leaf to return ERR_PTRs whenever the
parentid doesn't correspond to a class, so that we can detect it
earlier on and abort before qdisc_create is called.

[1] https://lore.kernel.org/netdev/d912cbd7-193b-4269-9857-525bee8bbb6a@gmail.com/

Fixes: 5e50da01d0 ("[NET_SCHED]: Fix endless loops (part 2): "simple" qdiscs")
Reported-by: syzbot+d8b58d7b0ad89a678a16@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/68663c93.a70a0220.5d25f.0857.GAE@google.com/
Reported-by: syzbot+5eccb463fa89309d8bdc@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/68663c94.a70a0220.5d25f.0858.GAE@google.com/
Reported-by: syzbot+1261670bbdefc5485a06@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/686764a5.a00a0220.c7b3.0013.GAE@google.com/
Reported-by: syzbot+15b96fc3aac35468fe77@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/686764a5.a00a0220.c7b3.0014.GAE@google.com/
Reported-by: syzbot+4dadc5aecf80324d5a51@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/netdev/68679e81.a70a0220.29cf51.0016.GAE@google.com/
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/20250707210801.372995-1-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-07-17 18:25:02 +02:00
arch powerpc: Fix struct termio related ioctl macros 2025-07-17 18:24:57 +02:00
block block: fix 'kmem_cache of name 'bio-108' already exists' 2025-04-10 14:29:37 +02:00
certs
crypto crypto: algif_hash - fix double free in hash_accept 2025-06-04 14:32:35 +02:00
Documentation scsi: ufs: core: Fix spelling of a sysfs attribute name 2025-07-17 18:24:58 +02:00
drivers drm/exynos: exynos7_drm_decon: add vblank check in IRQ handling 2025-07-17 18:25:01 +02:00
fs fix proc_sys_compare() handling of in-lookup dentries 2025-07-17 18:25:01 +02:00
include RDMA/core: Create and destroy counters in the ib_core 2025-07-17 18:24:59 +02:00
init bpfilter: match bit size of bpfilter_umh to that of the kernel 2025-07-17 18:24:51 +02:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:02:52 +01:00
kernel perf: Fix sample vs do_exit() 2025-06-27 11:02:58 +01:00
lib lib: test_objagg: Set error message in check_expect_hints_stats() 2025-07-17 18:24:56 +02:00
LICENSES
mm mm/huge_memory: fix dereferencing invalid pmd migration entry 2025-06-27 11:02:58 +01:00
net net/sched: Abort __tc_modify_qdisc if parent class does not exist 2025-07-17 18:25:02 +02:00
samples
scripts kbuild: use -MMD instead of -MD to exclude system headers from dependency 2025-07-17 18:24:51 +02:00
security selinux: fix selinux_xfrm_alloc_user() to set correct ctx_len 2025-06-27 11:02:56 +01:00
sound ALSA: sb: Force to disable DMAs once when DMA mode is changed 2025-07-17 18:24:57 +02:00
tools perf record: Fix incorrect --user-regs comments 2025-06-27 11:02:48 +01:00
usr kbuild: hdrcheck: fix cross build with clang 2025-07-17 18:24:51 +02:00
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
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COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS platform: Add Surface platform directory 2025-06-27 11:02:56 +01:00
Makefile Linux 5.4.295 2025-06-27 11:02:58 +01:00
README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.