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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.1 Subject: Re: [PATCH v2 0/3] Refactor __kmem_cache_create() and fix memory leak Content-Language: en-US To: Hyeonggon Yoo <42.hyeyoo@gmail.com>, Liu Shixin Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Rasmus Villemoes References: <20221031134747.3049593-1-liushixin2@huawei.com> From: Vlastimil Babka In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1667992627; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=nt/ta1l555vr4EsYp1C+UKFBUJaf1xMeh2se9hvTXV4=; b=1hGeWEBfWEnAjZsQMZWPQGqYivmu5oru784LboO6Mdl2cq1kLceEmHRkHQvdlFYnS6g3Z9 twonoggJMUIYqA0/wP1FzIiXhhoaG4Z6i0bBFCiXXaGALp7OOte9HoZqQy00/Dq3HLkVom Mk0lBm77IvXVTVcD+Dtl3zNJw46NVeI= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=A+ZNMvKz; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=v+hsFIFU; spf=pass (imf02.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1667992627; a=rsa-sha256; cv=none; b=R4v1D21t9gy7bF+9qW35EIeQ61cxgQEgzIxlbWDRzy2QCQ23MphzDTmJkeHzkhQ4dXj5SL 4dN2XCqOWzILVevSXcnFqXFwOxsUnheOrWvzzb0NYLeuYxSzBY71vwe+ArMA/ckv4NvyN1 2pGXQfcK8PDErqEV8qeGxjwX0WhB5ss= X-Rspam-User: X-Stat-Signature: gmkx8f8rqqz6ddi8zqrhsrjirzp66ut9 X-Rspamd-Queue-Id: E81BB80018 Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=A+ZNMvKz; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=v+hsFIFU; spf=pass (imf02.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.29 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Rspamd-Server: rspam07 X-HE-Tag: 1667992626-506840 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: On 11/3/22 14:23, Hyeonggon Yoo wrote: > On Wed, Nov 02, 2022 at 04:53:08PM +0800, Liu Shixin wrote: >> On 2022/11/2 15:46, Hyeonggon Yoo wrote: >> > On Mon, Oct 31, 2022 at 09:47:44PM +0800, Liu Shixin wrote: >> >> I found a memory leak of kobj->name in sysfs_slab_add() which is introduced >> >> by 80da026a8e5d ("mm/slub: fix slab double-free in case of duplicate sysfs filename"). >> >> Following the rules stated in the comment for kobject_init_and_add(): >> > Thank you for reporting this! Indeed it seems tried to fix double free but >> > introduced a leak. >> > >> >> If this function returns an error, kobject_put() must be called to >> >> properly clean up the memory associated with the object. >> >> >> >> We should use kobject_put() to free kobject. >> > But what to do if a cache is created early and later sysfs_slab_add() failed? >> > (Which is unlikely on normal condition) >> > >> > With this series it introduces use-after-free if sysfs_slab_add() in >> > slab_sysfs_init() failed. Should we just call BUG() or something like that? >> >> Thanks for your discovery, what I missed. > > You're welcome. > >> I prefer to panic directly, just as create_boot_cache() does. > > IMHO that should be nothing serious. but let's hear maintainers' opinion. > >> Of couse, if you want the system to continue booting, I think it's possible to distinguish them >> by slab_state. > > I'm afraid to make it more complex :( +Cc Rasmus who did a recent patch in this area. Thread starts here: https://lore.kernel.org/all/20221031134747.3049593-1-liushixin2@huawei.com/ As for me, I don't think we should be addung new BUG() or panic() in general, and especially not for a failing sysfs add. AFAICS create_boot_cache() might panic, but not because of sysfs, as that's delayed until slab_sysfs_init() and we don't panic anymore in the latter. So yeah, it could work to tell sysfs_slab_add() whether it should not do the kobject_put() as it's a boot cache. The slab_state should work. > >> Looking forward to your advice. >> Thanks, >> > >> >> But we can't simply add kobject_put() since it will free kmem_cache too. >> >> If we use kobject_put(), we need to skip other release functions. >> >> >> >> In this series, We refactor the code to separate sysfs_slab_add() and >> >> debugfs_slab_add() from __kmem_cache_create(), and then use kobject_put() >> >> to free kobject in sysfs_slab_add(). This can fix the memory leak of >> >> kobject->name. >> >> >> >> v1->v2: Fix build error reported by kernel test robot . >> >> >> >> Liu Shixin (3): >> >> mm/slab_common: Move cache_name to create_cache() >> >> mm/slub: Refactor __kmem_cache_create() >> >> mm/slub: Fix memory leak of kobj->name in sysfs_slab_add() >> >> >> >> include/linux/slub_def.h | 11 +++++++++ >> >> mm/slab_common.c | 44 ++++++++++++++++++---------------- >> >> mm/slub.c | 52 ++++++++++------------------------------ >> >> 3 files changed, 48 insertions(+), 59 deletions(-) >> >> >> >> -- >> >> 2.25.1 >> >> >> >