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Zijing Yin b2606c302d phonet/pep: disable BH around forwarded sk_receive_skb() 
commit dbc81608e3 upstream.

The networking receive path is usually run from softirq context, but
protocols that take the socket lock may have packets stored in the
backlog and processed later from process context. In that case
release_sock() -> __release_sock() drops the slock with spin_unlock_bh()
and then calls sk->sk_backlog_rcv() with bottom halves enabled.

Typical sk_backlog_rcv handlers process the socket whose backlog is
being drained, so the BH state at entry is irrelevant for the slocks
they touch. pep_do_rcv() is different: when the inbound skb targets an
existing PEP pipe, it forwards the skb to a different *child* socket
via sk_receive_skb(). That helper takes the child slock with
bh_lock_sock_nested(), which is just spin_lock_nested() and assumes BH
is already off. The same child slock therefore ends up acquired with
BH on (process path) and with BH off (softirq path):

  process context                   softirq context
  ---------------                   ---------------
  release_sock(listener)            __netif_receive_skb()
   __release_sock()                  phonet_rcv()
    spin_unlock_bh()                  __sk_receive_skb(listener)
    [BH now ENABLED]                  [BH already disabled]
    sk_backlog_rcv:                   sk_backlog_rcv:
     pep_do_rcv()                      pep_do_rcv()
      sk_receive_skb(child)             sk_receive_skb(child)
       bh_lock_sock_nested(child)        bh_lock_sock_nested(child)
       => SOFTIRQ-ON-W                   => IN-SOFTIRQ-W

Lockdep flags this as inconsistent lock state, and it can become a real
self-deadlock if a softirq on the same CPU tries to receive to the same
child socket while its slock is held in the BH-enabled path:

  WARNING: inconsistent lock state
  inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
   (slock-AF_PHONET/1){+.?.}-{3:3}, at: __sk_receive_skb+0x1cf/0x900
    __sk_receive_skb              net/core/sock.c:563
    sk_receive_skb                include/net/sock.h:2022 [inline]
    pep_do_rcv                    net/phonet/pep.c:675
    sk_backlog_rcv                include/net/sock.h:1190
    __release_sock                net/core/sock.c:3216
    release_sock                  net/core/sock.c:3815
    pep_sock_accept               net/phonet/pep.c:879

Wrap the forwarded sk_receive_skb() in local_bh_disable() /
local_bh_enable() so the child slock is always acquired with BH off.
local_bh_disable() nests safely on the softirq path.

Discovered via in-house syzkaller fuzzing; the same root cause also
on the linux-6.1.y syzbot dashboard as extid 44f0626dd6284f02663c.
Reproduced under KASAN + LOCKDEP + PROVE_LOCKING, reproducer:
https://pastebin.com/A3t8xzCR

Fixes: 9641458d3e ("Phonet: Pipe End Point for Phonet Pipes protocol")
Link: https://syzkaller.appspot.com/bug?extid=44f0626dd6284f02663c
Cc: stable@vger.kernel.org
Signed-off-by: Zijing Yin <yzjaurora@gmail.com>
Acked-by: Rémi Denis-Courmont <remi@remlab.net>
Reported-by: syzbot+9f4a135646b66c509935@syzkaller.appspotmail.com
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260519172635.86304-1-yzjaurora@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2026-06-01 17:35:46 +02:00
arch KVM: x86: Acquire SRCU in KVM_GET_MP_STATE to protect guest memory accesses 2026-06-01 17:35:46 +02:00
block blk-mq: use quiesced elevator switch when reinitializing queues 2026-06-01 17:35:09 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto crypto: af_alg - Cap AEAD AD length to 0x80000000 2026-06-01 17:35:44 +02:00
Documentation Documentation: fix a hugetlbfs reservation statement 2026-06-01 17:35:32 +02:00
drivers Bluetooth: hci_uart: fix UAFs and race conditions in close and init paths 2026-06-01 17:35:46 +02:00
fs sysfs: don't remove existing directory on update failure 2026-06-01 17:35:46 +02:00
include SUNRPC: Do not dereference non-socket transports in sysfs 2026-06-01 17:35:44 +02:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:21:45 +02:00
io_uring io_uring: prevent opcode speculation 2026-06-01 17:35:45 +02:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:05:26 +01:00
kernel audit: enforce AUDIT_LOCKED for AUDIT_TRIM and AUDIT_MAKE_EQUIV 2026-06-01 17:35:44 +02:00
lib lib/ts_kmp: fix integer overflow in pattern length calculation 2026-06-01 17:35:14 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() 2026-06-01 17:35:08 +02:00
net phonet/pep: disable BH around forwarded sk_receive_skb() 2026-06-01 17:35:46 +02:00
samples samples: mei: Fix building on musl libc 2025-08-28 16:24:07 +02:00
scripts scripts/dtc: Remove unused dts_version in dtc-lexer.l 2026-06-01 17:35:12 +02:00
security ima: check return value of crypto_shash_final() in boot aggregate 2026-06-01 17:35:34 +02:00
sound ALSA: asihpi: Fix potential OOB array access at reading cache 2026-06-01 17:35:46 +02:00
tools perf util: Kill die() prototype, dead for a long time 2026-06-01 17:35:35 +02:00
usr kbuild: hdrcheck: fix cross build with clang 2025-06-27 11:05:22 +01:00
virt KVM: Reject wrapped offset in kvm_reset_dirty_gfn() 2026-06-01 17:35:44 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Remove *.orig pattern from .gitignore 2024-10-17 15:11:10 +02:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS staging: rtl8712: Remove driver using deprecated API wext 2025-12-07 06:09:36 +09:00
Makefile Linux 5.15.208 2026-05-23 13:40:45 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.