linux-kernel - Re: [PATCH] uprobe: Find last occurrence of ':' when parsing uprobe PATH:OFFSET

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Date:   Fri, 13 Jan 2017 12:14:17 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kenny Yu <kennyyu@...com>
Cc:     <mingo@...hat.com>, <osandov@...com>,
        <linux-kernel@...r.kernel.org>, <kernel-team@...com>
Subject: Re: [PATCH] uprobe: Find last occurrence of ':' when parsing uprobe
 PATH:OFFSET

On Fri, 13 Jan 2017 08:58:34 -0800
Kenny Yu <kennyyu@...com> wrote:

> Previously, `create_trace_uprobe` found the *first* occurence
> of the ':' character when parsing `PATH:OFFSET` for a uprobe.
> However, if the path contains a ':' character, then the function
> would parse the path incorrectly. Even worse, if the path does not
> exist, the subsequent call to `kern_path()` would set `ret` to
> `ENOENT`, leading to very cryptic errno values in user space.
> 
> The fix is to find the *last* occurence of ':'.
> 
> How to repro:: The write fails with "No such file or directory", suggesting
> incorrectly that the `uprobe_events` file does not exist.
> 
>   $ mkdir testing && cd testing
>   $ cp /bin/bash .
>   $ cp /bin/bash ./bash:with:colon
>   $ echo "p:uprobes/p__root_testing_bash_0x6 /root/testing/bash:0x6" > /sys/kernel/debug/tracing/uprobe_events     # this works
>   $ echo "p:uprobes/p__root_testing_bash_with_colon_0x6 /root/testing/bash:with:colon:0x6" >> /sys/kernel/debug/tracing/uprobe_events     # this doesn't
>   -bash: echo: write error: No such file or directory
> 
> With the patch:
> 
>   $ echo "p:uprobes/p__root_testing_bash_0x6 /root/testing/bash:0x6" > /sys/kernel/debug/tracing/uprobe_events     # this still works
>   $ echo "p:uprobes/p__root_testing_bash_with_colon_0x6 /root/testing/bash:with:colon:0x6" >> /sys/kernel/debug/tracing/uprobe_events     # this works now too!
>   $ cat /sys/kernel/debug/tracing/uprobe_events
>   p:uprobes/p__root_testing_bash_0x6 /root/testing/bash:0x0000000000000006
>   p:uprobes/p__root_testing_bash_with_colon_0x6 /root/testing/bash:with:colon:0x0000000000000006
> 

Thanks! I'll add this to my queue.

-- Steve