linux-kernel - Re: [PATCH] uprobe: add support for overlayfs

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Date:   Mon, 5 Mar 2018 14:59:05 -0500
From:   Josef Bacik <josef@...icpanda.com>
To:     Howard McLauchlan <hmclauchlan@...com>
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, kernel-team@...com,
        Yonghong Song <yhs@...com>, Josef Bacik <jbacik@...com>,
        Omar Sandoval <osandov@...ndov.com>
Subject: Re: [PATCH] uprobe: add support for overlayfs

On Tue, Feb 27, 2018 at 04:40:14PM -0800, Howard McLauchlan wrote:
> uprobes cannot successfully attach to binaries located in a directory
> mounted with overlayfs.
> 
> To verify, create directories for mounting overlayfs
> (upper,lower,work,merge), move some binary into merge/ and use readelf
> to obtain some known instruction of the binary. I used /bin/true and the
> entry instruction(0x13b0):
> 
> 	$ mount -t overlay overlay -o lowerdir=lower,upperdir=upper,workdir=work merge
> 	$ cd /sys/kernel/debug/tracing
> 	$ echo 'p:true_entry PATH_TO_MERGE/merge/true:0x13b0' > uprobe_events
> 	$ echo 1 > events/uprobes/true_entry/enable
> 
> This returns 'bash: echo: write error: Input/output error' and dmesg
> tells us 'event trace: Could not enable event true_entry'
> 
> This change makes create_trace_uprobe() look for the real inode of a
> dentry. In the case of normal filesystems, this simplifies to just
> returning the inode. In the case of overlayfs(and similar fs) we will
> obtain the underlying dentry and corresponding inode, upon which uprobes
> can successfully register.
> 
> Running the example above with the patch applied, we can see that the
> uprobe is enabled and will output to trace as expected.
> 
> Signed-off-by: Howard McLauchlan <hmclauchlan@...com>

Reviewed-by: Josef Bacik <jbacik@...com>

Thanks,

Josef