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Tue, 22 Apr 2025 22:38:45 -0700 (PDT) Date: Wed, 23 Apr 2025 08:38:42 +0300 From: Dan Carpenter To: Su Hui Cc: Christophe JAILLET , SeongJae Park , akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] mm/damon/sysfs-schemes: using kmalloc_array() and size_add() Message-ID: References: <501ea9b1-017b-4517-8de4-7056803e7127@wanadoo.fr> <21407408-78e4-48eb-8296-fcddc702ae25@nfschina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <21407408-78e4-48eb-8296-fcddc702ae25@nfschina.com> X-Stat-Signature: xe5x651qthekmbfub14r9bbbmzhpksp1 X-Rspamd-Queue-Id: 0B2C5100006 X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1745386727-968964 X-HE-Meta: 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 FX1geDhH oaDDWQ+Dj7u2w2sZXi8K9EXvMVgqyruc0M8HWmYrj+l6OuAhXPgeECqwnldnxp2ZPxLRkzlkA5Mo6vOLWwAd3S2M3XwISjGUSL3vKmBbQU4si3/5ZqUfJzViEBOtkQPvzbUSsrGiUEY0Xrlbf4EV8TIHy/D5Czn8F6ItaPuY2gcxJ9Pu4BFs9qArtSeln6Fu6dK1aL/oO0zc3hypnQUd09e+nqSTdv+HgAAgnET4UDaUh1Dg97v3X6zNCMmep0L4by2SDNbH1q1VL/UTV83+E0pJ7kP+quMLYSSzaq0kurR5DicdOeNtXyfgZ2P2SR1iCFZOc7bAs48D2NT54m07S95m0B02o8TFHDB/hZA2ctX5twKr31Dr9AhCar/M7ld6EoWkCTwsK7DDT7PTTgk2LqOzuql+NPP3lJrTKWqgNDQii3L3efC9av5jdBhC48t2SZcxCFznn5RpUuJkK1yIaw03Kbg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 23, 2025 at 10:04:56AM +0800, Su Hui wrote: > On 2025/4/23 02:50, Christophe JAILLET wrote: > > Le 22/04/2025 à 20:23, SeongJae Park a écrit : > > > On Tue, 22 Apr 2025 13:44:39 +0300 Dan Carpenter > > > wrote: > > > > > > > On Tue, Apr 22, 2025 at 01:38:05PM +0300, Dan Carpenter wrote: > > > > > On Mon, Apr 21, 2025 at 02:24:24PM +0800, Su Hui wrote: > > > > > > It's safer to using kmalloc_array() and size_add() because it can > > > > > > prevent possible overflow problem. > > > > > > > > > > > > Signed-off-by: Su Hui > > > [...] > > > > > > --- a/mm/damon/sysfs-schemes.c > > > > > > +++ b/mm/damon/sysfs-schemes.c > > > > > > @@ -465,7 +465,8 @@ static ssize_t > > > > > > memcg_path_store(struct kobject *kobj, > > > > > >   { > > > > > >       struct damon_sysfs_scheme_filter *filter = container_of(kobj, > > > > > >               struct damon_sysfs_scheme_filter, kobj); > > > > > > -    char *path = kmalloc(sizeof(*path) * (count + 1), GFP_KERNEL); > > > > > > +    char *path = kmalloc_array(size_add(count, 1), sizeof(*path), > > > > > > +                   GFP_KERNEL); > > > > > > > > > > Count is clamped in rw_verify_area(). > > > > > > > > > > Smatch does a kind of ugly hack to handle rw_verify_area() > > > > > which is that > > > > > it says neither the count nor the pos can be more than 1G. > > > > > And obviously > > > > > files which are larger than 2GB exist but pretending they > > > > > don't silences > > > > > all these integer overflow warnings. > > > > > > > > > > > > > Actually rw_verify_area() ensures that "pos + count" can't > > > > overflow.  But > > > > here we are multiplying.  Fortunately, we are multiplying by 1 > > > > so that's > > > > safe and also count can't be larger than PAGE_SIZE here which is > > > > safe as > > > > well. > > > > > > Thank you for adding these details, Dan.  I understand the > > > size_add() change > > > can make warnings slience, though it is not really fixing a real > > > bug.  So I > > > believe there is no action item to make a change to this patch. > > > Maybe making > > > the commit message more clarified can be helpful, though? > > > > > > Please let me know if I'm misunderstanding your point and/or you > > > want some > > > changes. > > > > As sizeof(*path) = 1, maybe, just change it to: > >     char *path = kmalloc(count + 1, GFP_KERNEL); > Maybe nothing should change? Yeah. No need to change. Sysfs buffers are always a page size and count is <= PAGE_SIZE. Generally, it's one of the pieces of trivia that people should know. That's how sysfs_emit() works. regards, dan carpenter