linux-kernel - Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for folio split

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Message-ID: <Zirb4GNjubOJzdoR@bombadil.infradead.org>
Date: Thu, 25 Apr 2024 15:40:32 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: Zi Yan <ziy@...dia.com>
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org, fstests@...r.kernel.org,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	willy@...radead.org, hare@...e.de, john.g.garry@...cle.com,
	p.raghav@...sung.com, da.gomez@...sung.com
Subject: Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for
 folio split

On Wed, Apr 24, 2024 at 09:03:51PM -0400, Zi Yan wrote:
> On 24 Apr 2024, at 18:54, Luis Chamberlain wrote:
> 
> > If the file entry is too long we may easily end up going out of bounds
> > and crash after strsep() on sscanf(). To avoid this ensure we bound the
> > string to an expected length before we use sscanf() on it.
> >
> > Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> > ---
> >  mm/huge_memory.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 9e9879d2f501..8386d24a163e 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -3623,6 +3623,7 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
> >  		char file_path[MAX_INPUT_BUF_SZ];
> >  		pgoff_t off_start = 0, off_end = 0;
> >  		size_t input_len = strlen(input_buf);
> > +		size_t max_left_over;
> >
> >  		tok = strsep(&buf, ",");
> >  		if (tok) {
> > @@ -3632,6 +3633,14 @@ static ssize_t split_huge_pages_write(struct file *file, const char __user *buf,
> >  			goto out;
> >  		}
> >
> > +		max_left_over = MAX_INPUT_BUF_SZ - strlen(file_path);
> > +		if (!buf ||
> > +		    strnlen(buf, max_left_over) < 7 ||
> 
> What is this magic number 7? strlen("0xN,0xN") as the minimal input string size?
> Maybe use sizeof("0xN,0xN") - 1 instead?

Sure and I forgot the fixes tag, will send a v2.

  Luis