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([2405:201:682f:389d:8374:24de:cb92:e673]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7b9250cd969sm18467014b3a.23.2025.11.18.22.40.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Nov 2025 22:40:26 -0800 (PST) From: Deepanshu Kartikey To: rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+a72c325b042aae6403c7@syzkaller.appspotmail.com Subject: [PATCH] tracing: Fix WARN_ON in tracing_buffers_mmap_close for split VMAs Date: Wed, 19 Nov 2025 12:10:19 +0530 Message-ID: <20251119064019.25904-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When a VMA is split (e.g., by partial munmap or MAP_FIXED), the kernel calls vm_ops->close on each portion. For trace buffer mappings, this results in ring_buffer_unmap() being called multiple times while ring_buffer_map() was only called once. This causes ring_buffer_unmap() to return -ENODEV on subsequent calls because user_mapped is already 0, triggering a WARN_ON. Trace buffer mappings cannot support partial mappings because the ring buffer structure requires the complete buffer including the meta page. Fix this by adding a may_split callback that returns -EINVAL to prevent VMA splits entirely. Closes: https://syzkaller.appspot.com/bug?extid=a72c325b042aae6403c7 Tested-by: syzbot+a72c325b042aae6403c7@syzkaller.appspotmail.com Reported-by: syzbot+a72c325b042aae6403c7@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey --- kernel/trace/trace.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index d1e527cf2aae..304e93597126 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -8781,8 +8781,18 @@ static void tracing_buffers_mmap_close(struct vm_area_struct *vma) put_snapshot_map(iter->tr); } +static int tracing_buffers_may_split(struct vm_area_struct *vma, unsigned long addr) +{ + /* + * Trace buffer mappings require the complete buffer including + * the meta page. Partial mappings are not supported. + */ + return -EINVAL; +} + static const struct vm_operations_struct tracing_buffers_vmops = { .close = tracing_buffers_mmap_close, + .may_split = tracing_buffers_may_split, }; static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma) -- 2.43.0