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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: cf9f0f7c4c ("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: syzbot+a72c325b042aae6403c7@syzkaller.appspotmail.com
Reported-by: syzbot+a72c325b042aae6403c7@syzkaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Deepanshu Kartikey 2025-11-19 12:10:19 +05:30 committed by Steven Rostedt (Google)
parent dcb6fa37fd
commit b042fdf18e
1 changed files with 10 additions and 0 deletions
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10
kernel/trace/trace.c
View File

@ -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)