linux-kernel - Re: [PATCH v9 2/4] Uprobes/sdt: Prevent multiple reference counter for same uprobe

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Message-ID: <CAPhsuW4QbT+0wHYW-A7G8z-Xp=8M+0w1Efmc1006PbqNTfOSxg@mail.gmail.com>
Date:   Sun, 19 Aug 2018 22:54:35 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>, mhiramat@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org,
        open list <linux-kernel@...r.kernel.org>,
        ananth@...ux.vnet.ibm.com,
        Alexis Berlemont <alexis.berlemont@...il.com>,
        naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com
Subject: Re: [PATCH v9 2/4] Uprobes/sdt: Prevent multiple reference counter
 for same uprobe

On Sun, Aug 19, 2018 at 9:42 PM, Ravi Bangoria
<ravi.bangoria@...ux.ibm.com> wrote:
> We assume to have only one reference counter for one uprobe.
> Don't allow user to register multiple uprobes having same
> inode+offset but different reference counter.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
> Acked-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Reviewed-by: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Song Liu <songliubraving@...com>

> ---
>  kernel/events/uprobes.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 35065febcb6c..ecee371a59c7 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -679,6 +679,16 @@ static struct uprobe *insert_uprobe(struct uprobe *uprobe)
>         return u;
>  }
>
> +static void
> +ref_ctr_mismatch_warn(struct uprobe *cur_uprobe, struct uprobe *uprobe)
> +{
> +       pr_warn("ref_ctr_offset mismatch. inode: 0x%lx offset: 0x%llx "
> +               "ref_ctr_offset(old): 0x%llx ref_ctr_offset(new): 0x%llx\n",
> +               uprobe->inode->i_ino, (unsigned long long) uprobe->offset,
> +               (unsigned long long) cur_uprobe->ref_ctr_offset,
> +               (unsigned long long) uprobe->ref_ctr_offset);
> +}
> +
>  static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
>                                    loff_t ref_ctr_offset)
>  {
> @@ -698,6 +708,12 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
>         cur_uprobe = insert_uprobe(uprobe);
>         /* a uprobe exists for this inode:offset combination */
>         if (cur_uprobe) {
> +               if (cur_uprobe->ref_ctr_offset != uprobe->ref_ctr_offset) {
> +                       ref_ctr_mismatch_warn(cur_uprobe, uprobe);
> +                       put_uprobe(cur_uprobe);
> +                       kfree(uprobe);
> +                       return ERR_PTR(-EINVAL);
> +               }
>                 kfree(uprobe);
>                 uprobe = cur_uprobe;
>         }
> @@ -1112,6 +1128,9 @@ static int __uprobe_register(struct inode *inode, loff_t offset,
>         uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
>         if (!uprobe)
>                 return -ENOMEM;
> +       if (IS_ERR(uprobe))
> +               return PTR_ERR(uprobe);
> +
>         /*
>          * We can race with uprobe_unregister()->delete_uprobe().
>          * Check uprobe_is_active() and retry if it is false.
> --
> 2.14.4
>