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Wed, 01 Apr 2026 06:44:27 -0700 (PDT) Received: from computer ([2a09:bac5:40b2:a82::10c:35]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c76917d843esm13795063a12.29.2026.04.01.06.44.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Apr 2026 06:44:27 -0700 (PDT) Date: Wed, 1 Apr 2026 19:14:15 +0530 From: Varun R Mallya To: bpf@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kpsingh@kernel.org, mattbobrowski@google.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, memxor@gmail.com, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, linux-trace-kernel@vger.kernel.org Subject: [BUG] bpf: kprobe_multi allows BPF_F_SLEEPABLE programs, causing sleeping-in-atomic splat Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Hi, I found a bug in the kprobe_multi BPF link creation path where the kernel fails to reject programs with BPF_F_SLEEPABLE set. kprobe.multi programs run in an atomic/RCU context and cannot sleep. However, bpf_link_create() with BPF_TRACE_KPROBE_MULTI does not validate whether the program being attached has BPF_F_SLEEPABLE set. This allows sleepable helpers such as bpf_copy_from_user() to be invoked from a non-sleepable context, triggering a "sleeping function called from invalid context" splat. Reproducer: /* crash.bpf.c */ SEC("kprobe.multi") int handle_kprobe_multi_crash(struct pt_regs *ctx) { char buf[16]; int ret; ret = bpf_copy_from_user(buf, sizeof(buf), (void *)ctx->sp); bpf_printk("bpf_copy_from_user ret: %d\n", ret); return 0; } /* loader: manually set BPF_F_SLEEPABLE before load, then attach via bpf_link_create() with BPF_TRACE_KPROBE_MULTI */ bpf_program__set_flags(prog, BPF_F_SLEEPABLE); Kernel output (bpf-next 7.0.0-rc5+): [ 483.577248] BUG: sleeping function called from invalid context at ./include/linux/uaccess.h: 169 [ 483.577364] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo [ 483.577420] preempt_count: 1, expected: 0 [ 483.577453] RCU nest depth: 2, expected: 0 [ 483.577486] INFO: lockdep is turned off. Attachment successful! The bug is confirmed. Check 'sudo dmesg -w' for BPF prints and warnings. Triggering v[ 483.577569] CfsPU: 7 UID: 0 PID: 1787 Comm: sudo Tainted: G W _ rea7.0.0-rc5+ #4 PREEMPT(full) d[ 483.577571] T.ainted: [W]=WARN.. Su[ 483.577572] Hrvardware name: Bochs Bochs, BIOS iBochs 01/01/2011v [ 483.577573] Call Trace: [ 483.577575] e [ 483.577578] d!dump_stack_lvl+0x54/0x70 [ 483.577582] If __might_resched+b0x200/0x220 p[ 483.577585] f__might_fault+0x_c2c/0x80 o[ 483.577587] p_copy_from_user+y0x23/0x80 _[ 483.577591] bpf_copy_from_user+0x27/0x50 [ 483.577594] fbpf_prog_1906cf6roa66546b5e_handlem__kprobe_multi_crash+0x33/0x4d u[ 483.577596] skprobe_multi_linek_handler+0x15d/r re0x260 [ 483.577599] t? kprobe_multi_lurink_handler+0x99n/0x260 [ 483.577602] e? __pfx_vfs_readd +0x10/0x10 0[ 483.577604] in? ksys_read+0x7c/0x100 [ 483.577605] dm? vfs_read+0x4/0esg, x360 t[ 483.577607] fprobe_ftrace_entry+0x3b8/0x480 [ 483.577609] h? ksys_read+0x7ce /0x100 e[ 483.577610] x? fprobe_ftrace_pentry+0x93/0x480l o[ 483.577612] it? lock_release+0x42/0x330 [ 483.577615] ? vfs_read+0x9/0wx360 o[ 483.577616] r? __x64_sys_rt_sigaction+0xde/0xke120 [ 483.577619] ? vfs_read+0x9/0x360 [ 483.577620] d? ksys_read+0x7c./0x100 [ 483.577622] ? do_syscall_64+0x143/0xf80 [ 483.577624] ? entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 483.577625] ? trace_irq_disable+0x1d/0xc0 [ 483.577627] ? entry_SYSCALL_64_after_hwframe+0x77/0x7f [ 483.577631] I am sending in a patch that fixes this. Signed-off-by: Varun R Mallya