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[192.26.29.3]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4601f2f2710sm32485831f8f.14.2026.06.07.01.27.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 07 Jun 2026 01:27:08 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Sun, 07 Jun 2026 10:27:07 +0200 Message-Id: Cc: , "Alexei Starovoitov" , "Daniel Borkmann" , "Andrii Nakryiko" , "Martin KaFai Lau" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Yonghong Song" , "Jiri Olsa" , "John Fastabend" , "Stanislav Fomichev" , Subject: Re: [PATCH bpf-next] bpf: reject sleepable BPF_LSM_CGROUP programs at load time From: "Kumar Kartikeya Dwivedi" To: "Song Liu" , "David Windsor" X-Mailer: aerc 0.21.0 References: <20260605145707.608579-1-dwindsor@gmail.com> In-Reply-To: On Fri Jun 5, 2026 at 11:40 PM CEST, Song Liu wrote: > On Fri, Jun 5, 2026 at 7:57=E2=80=AFAM David Windsor = wrote: >> >> The cgroup shim runs under rcu_read_lock_dont_migrate(), so we should >> not attach any sleepable BPF programs there. Add support to the verifier >> to explicitly reject attempts to load sleepable BPF programs destined >> for LSM cgroup attachment. >> >> Without this, we get the following splat from a BPF_LSM_CGROUP >> program marked BPF_F_SLEEPABLE attached to file_open when it calls >> bpf_get_dentry_xattr(): >> >> BUG: sleeping function called from invalid context at kernel/locking/r= wsem.c:1567 >> in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 34317, name: lo= ad >> preempt_count: 0, expected: 0 >> RCU nest depth: 2, expected: 0 >> Call Trace: >> down_read+0x76/0x480 >> ext4_xattr_get+0x11f/0x700 >> __vfs_getxattr+0xf0/0x150 >> bpf_get_dentry_xattr+0xbb/0xf0 >> bpf_prog_e76a298dac9218c6_test_open+0x6a/0x85 >> __cgroup_bpf_run_lsm_current+0x326/0x840 >> bpf_trampoline_6442534646+0x62/0x14d >> security_file_open+0x34/0x60 >> do_dentry_open+0x340/0x1260 >> vfs_open+0x7a/0x440 >> path_openat+0x1bac/0x30a0 >> >> libbpf provides a .s named section variant for every sleepable >> program type except lsm_cgroup, reflecting that per-cgroup LSM programs >> are intended to only run in a non-sleepable context. >> >> The above splat was obtained by bypassing libbpf by using bpf(2) >> directly. >> >> Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor") >> Signed-off-by: David Windsor > > We should add a "__failure __msg(...)" selftest for the reject case. > David, Please follow up with selftest for the fix.