From: "Ahmed S. Darwish" <darwish.07@gmail.com>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 11/13] proc: readdir /proc/*/task
Date: Tue, 28 Aug 2018 13:04:40 +0000 [thread overview]
Message-ID: <20180828130440.GA6464@darwi-kernel> (raw)
In-Reply-To: <20180828123622.GA2087@darwi-kernel>
On Tue, Aug 28, 2018 at 12:36:22PM +0000, Ahmed S. Darwish wrote:
> On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> > ---
> > fs/proc/base.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
>
> Missing description and S-o-b. Further comments below..
>
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 33f444721965..668e465c86b3 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
> > for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
> > task;
> > task = next_tid(task), ctx->pos++) {
> > - char name[10 + 1];
> > - unsigned int len;
> > + char name[10], *p = name + sizeof(name);
> > +
>
> Multiple issues:
>
> - len should be 11, as was in the original code
> (0xffffffff = 4294967295, 10 letters)
>
> - while we're at it, let's use a constant for the '11' instead of
> mysterious magic numbers
>
> - 'p' is clearly overflowing the stack here
>
See below:
> > tid = task_pid_nr_ns(task, ns);
> > - len = snprintf(name, sizeof(name), "%u", tid);
> > - if (!proc_fill_cache(file, ctx, name, len,
> > + p = _print_integer_u32(p, tid);
> > + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
>
> You're replacing snprintf() code __that did proper len checking__
> with code that does not. That's not good.
>
> I can't see how the fourth proc_fill_cache() parameter, ``name +
> sizeof(name)'' safely ever replace the original 'len' parameter.
> It's a pointer value .. (!)
>
Ok, there's a "- p" in the end, so the length looks to be Ok.
Nonetheless, the whole patch series is introducing funny code
like:
+/*
+ * Print an integer in decimal.
+ * "p" initially points PAST THE END OF THE BUFFER!
+ *
+ * DO NOT USE THESE FUNCTIONS!
+ *
+ * Do not copy these functions.
+ * Do not document these functions.
+ * Do not move these functions to lib/ or elsewhere.
+ * Do not export these functions to modules.
+ * Do not tell anyone about these functions.
+ */
+noinline
+char *_print_integer_u32(char *p, u32 x)
+{
+ do {
+ *--p = '0' + (x % 10);
+ x /= 10;
+ } while (x != 0);
+ return p;
+}
And thus the code using these functions is throwing invalid
past-the-stack pointers and strings with no NULL terminators
like there's no tomorrow...
IMHO It's an accident waiting to happen to sprinkle pointers
like that everywhere. Are we really in a super hot path to
justify all that?
/me confused
--
Darwish
http://darwish.chasingpointers.com
next prev parent reply other threads:[~2018-08-28 13:04 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-27 23:14 [PATCH 01/13] seq_file: rewrite seq_puts() in terms of seq_write() Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 02/13] proc: apply seq_puts() whenever possible Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 03/13] proc: rename "p" variable in proc_readfd_common() Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 04/13] proc: rename "p" variable in proc_map_files_readdir() Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 05/13] proc: new and improved way to print decimals Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 06/13] proc: convert /proc/self to _print_integer() Alexey Dobriyan
2018-08-29 9:50 ` David Laight
2018-08-30 13:13 ` Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 07/13] proc: convert /proc/thread-self " Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 08/13] proc: convert /proc/*/fd " Alexey Dobriyan
2018-08-27 23:14 ` [PATCH 09/13] proc: convert dentry flushing on exit " Alexey Dobriyan
2018-08-27 23:15 ` [PATCH 10/13] proc: convert readdir /proc " Alexey Dobriyan
2018-08-27 23:15 ` [PATCH 11/13] proc: readdir /proc/*/task Alexey Dobriyan
2018-08-28 12:36 ` Ahmed S. Darwish
2018-08-28 13:04 ` Ahmed S. Darwish [this message]
2018-08-28 19:35 ` Alexey Dobriyan
2018-08-29 23:43 ` Andrew Morton
2018-08-30 13:20 ` Alexey Dobriyan
2018-08-28 19:31 ` Alexey Dobriyan
2018-08-27 23:15 ` [PATCH 12/13] proc: convert /proc/*/statm to _print_integer() Alexey Dobriyan
2018-08-27 23:15 ` [PATCH 13/13] proc: convert /proc/*/task/*/children " Alexey Dobriyan
2018-08-28 18:24 ` [PATCH 01/13] seq_file: rewrite seq_puts() in terms of seq_write() Joe Perches
2018-08-28 20:48 ` Joe Perches
2018-09-03 14:17 ` Alexey Dobriyan
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