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([147.46.174.222]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8455382780asm2969123b3a.46.2026.06.19.11.44.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jun 2026 11:44:42 -0700 (PDT) From: Sechang Lim To: Steven Rostedt , Masami Hiramatsu Cc: Mathieu Desnoyers , Heiko Carstens , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: [PATCH] tracing/fprobe: Fix NULL pointer dereference in fprobe_fgraph_entry() Date: Fri, 19 Jun 2026 18:44:24 +0000 Message-ID: <20260619184425.3824774-1-rhkrqnwk98@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit fprobe_fgraph_entry() sizes a shadow-stack reservation in one walk of the per-ip fprobe list and fills it in a second walk, both under rcu_read_lock() only. A fprobe registered on an already-live ip can become visible between the two walks, so the fill walk processes an exit_handler the sizing walk did not count and used runs past reserved_words. If the sizing walk counted nothing, fgraph_data is NULL and the first write_fprobe_header() faults: Oops: general protection fault, probably for non-canonical address ... KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:fprobe_fgraph_entry+0xa38/0xf10 kernel/trace/fprobe.c:167 Call Trace: function_graph_enter_regs+0x44c/0xa10 kernel/trace/fgraph.c:677 ftrace_graph_func+0xc5/0x140 arch/x86/kernel/ftrace.c:671 __kernel_text_address+0x9/0x40 kernel/extable.c:78 arch_stack_walk+0x117/0x170 arch/x86/kernel/stacktrace.c:26 kmem_cache_free+0x188/0x580 mm/slub.c:6378 tcp_data_queue+0x18d/0x6550 net/ipv4/tcp_input.c:5590 [...] The list cannot be frozen across the two walks, so skip a node that does not fit the reservation and count it as missed. Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer") Signed-off-by: Sechang Lim --- kernel/trace/fprobe.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c index f378613ad120..f215990b9061 100644 --- a/kernel/trace/fprobe.c +++ b/kernel/trace/fprobe.c @@ -613,6 +613,16 @@ static int fprobe_fgraph_entry(struct ftrace_graph_ent *trace, struct fgraph_ops continue; data_size = fp->entry_data_size; + /* + * The list may have grown since it was sized, so this node + * may not fit. Skip it as missed rather than overrun the + * reservation. + */ + if (fp->exit_handler && + used + FPROBE_HEADER_SIZE_IN_LONG + SIZE_IN_LONG(data_size) > reserved_words) { + fp->nmissed++; + continue; + } if (data_size && fp->exit_handler) data = fgraph_data + used + FPROBE_HEADER_SIZE_IN_LONG; else -- 2.43.0