Commit b042fdf1 authored by Deepanshu Kartikey's avatar Deepanshu Kartikey Committed by Steven Rostedt (Google)
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tracing: Fix WARN_ON in tracing_buffers_mmap_close for split VMAs 

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.

Cc: stable@vger.kernel.org
Fixes: cf9f0f7c ("tracing: Allow user-space mapping of the ring-buffer")
Link: https://patch.msgid.link/20251119064019.25904-1-kartikey406@gmail.com
Closes: https://syzkaller.appspot.com/bug?extid=a72c325b042aae6403c7


Tested-by: default avatar <syzbot+a72c325b042aae6403c7@syzkaller.appspotmail.com>
Reported-by: default avatar <syzbot+a72c325b042aae6403c7@syzkaller.appspotmail.com>
Signed-off-by: default avatarDeepanshu Kartikey <kartikey406@gmail.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent dcb6fa37

kernel/trace/trace.c

+10 −0
Original line number Diff line number Diff line
@@ -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)