From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.223.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9DEF931A542 for ; Wed, 4 Feb 2026 21:34:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=195.135.223.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770240854; cv=none; b=jZhiup4MaIq8YaNJGWEGKV2yhCTHCtCaTOCUy5+5mLUX8TJvt0ihV519tqSB7P6wNuLahc0zQM47ezop53kTndUgALWKaS0aFgdEHFUj6qfwsK9J8Ws+HxvqU88qdYY0WUci2GBz0je2Cl32FTqb99Bp8altK8vrHQVfOsw2cP4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770240854; c=relaxed/simple; bh=090FvL7e9Y9BulQrXSpbPgQzy7heKWmqCpLkJV+/tEQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uEFOfevlexb8y3LzMufdkMvpxSR6qAr6gqGZAqaDrIrL7ZnEuEIM1tcsvE6GS/SZ+YXtNPdTiMvXm7tJvVKifhrUb22o2Fm7tYu4Oez9Ol+eVIpLegoyZ208z0KXAwD0wcO3iFLkht0ziRC4fqt9ugYXIsRqeU4iWP67FscRthI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz; spf=pass smtp.mailfrom=suse.cz; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=rd1JcDki; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=jV7dAsbm; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b=rd1JcDki; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b=jV7dAsbm; arc=none smtp.client-ip=195.135.223.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.cz Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="rd1JcDki"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="jV7dAsbm"; dkim=pass (1024-bit key) header.d=suse.cz header.i=@suse.cz header.b="rd1JcDki"; dkim=permerror (0-bit key) header.d=suse.cz header.i=@suse.cz header.b="jV7dAsbm" Received: from imap1.dmz-prg2.suse.org (unknown [10.150.64.97]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id C10725BD6A; Wed, 4 Feb 2026 21:34:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1770240851; h=from:from:reply-to: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:autocrypt:autocrypt; bh=HpECjgLDyQROSSuqqkM4/AP66DpIGAvnkeFoALvGbNg=; b=rd1JcDkivGYAJX5jTLUdHvhNoNBnESnBxYOBd4TCFsPdlZSqPBrWPZCcXosVhjWTN64mpj N6esqOxI7L3PrwCKRtZLuCAblYVVC3CHa9zkvF51XNIKtDQZbCkR0yzkivr6SbuAaRfVdZ re9BK/79dzOXnj5H1MHtLliT3jrBxe4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1770240851; h=from:from:reply-to: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:autocrypt:autocrypt; bh=HpECjgLDyQROSSuqqkM4/AP66DpIGAvnkeFoALvGbNg=; b=jV7dAsbmHYoDnaCfHbUJkPDTF8BxybGNjMGYXEO73dgLx+kSjXddSLVJIlzMD0j30cYn5X E8krLh5HZwgB/ZCw== Authentication-Results: smtp-out2.suse.de; none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1770240851; h=from:from:reply-to: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:autocrypt:autocrypt; bh=HpECjgLDyQROSSuqqkM4/AP66DpIGAvnkeFoALvGbNg=; b=rd1JcDkivGYAJX5jTLUdHvhNoNBnESnBxYOBd4TCFsPdlZSqPBrWPZCcXosVhjWTN64mpj N6esqOxI7L3PrwCKRtZLuCAblYVVC3CHa9zkvF51XNIKtDQZbCkR0yzkivr6SbuAaRfVdZ re9BK/79dzOXnj5H1MHtLliT3jrBxe4= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1770240851; h=from:from:reply-to: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:autocrypt:autocrypt; bh=HpECjgLDyQROSSuqqkM4/AP66DpIGAvnkeFoALvGbNg=; b=jV7dAsbmHYoDnaCfHbUJkPDTF8BxybGNjMGYXEO73dgLx+kSjXddSLVJIlzMD0j30cYn5X E8krLh5HZwgB/ZCw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id A2A143EA63; Wed, 4 Feb 2026 21:34:11 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id FY1YJ1O7g2kqagAAD6G6ig (envelope-from ); Wed, 04 Feb 2026 21:34:11 +0000 Message-ID: <82dafb42-ca29-4ea7-9c1f-114c10443237@suse.cz> Date: Wed, 4 Feb 2026 22:34:11 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slub: zero-initialize slab object extensions to fix KMSAN Content-Language: en-US To: Osama Abdelkader , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: syzbot+6e04171f00f33c0d62fb@syzkaller.appspotmail.com References: <20260204195751.188219-1-osama.abdelkader@gmail.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20260204195751.188219-1-osama.abdelkader@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Score: -2.80 X-Spamd-Result: default: False [-2.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCPT_COUNT_SEVEN(0.00)[9]; FREEMAIL_TO(0.00)[gmail.com,linux-foundation.org,gentwo.org,google.com,linux.dev,oracle.com,kvack.org,vger.kernel.org]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TAGGED_RCPT(0.00)[6e04171f00f33c0d62fb]; MID_RHS_MATCH_FROM(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TO_DN_SOME(0.00)[] X-Spam-Level: X-Spam-Flag: NO On 2/4/26 20:57, Osama Abdelkader wrote: > KMSAN reports uninitialized reads in __memcg_slab_free_hook > when freeing sigqueue objects. Although kmalloc_nolock(__GFP_ZERO) > and kcalloc_node normally zero memory, some allocation paths > (fallbacks, early boot, reused slabs, or races) may leave objcg undefined. > > Explicitly memset the obj_exts array after allocation to guarantee no > uninitialized reads in __memcg_slab_free_hook and preserve correct memcg > accounting. > > Reported-by: syzbot+6e04171f00f33c0d62fb@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=6e04171f00f33c0d62fb > Signed-off-by: Osama Abdelkader > --- > mm/slub.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index f77b7407c51b..e66d17ee7fa8 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -2123,7 +2123,17 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, > vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp, > slab_nid(slab)); > } > - if (!vec) { > + /* > + * Explicitly zero the obj_exts array to ensure KMSAN recognizes it > + * as initialized. Although kmalloc_nolock and kcalloc_node normally > + * zero memory, KMSAN may not track this initialization in all cases, > + * especially during early boot or with certain allocation paths. > + * This explicit memset ensures KMSAN sees the initialization and > + * prevents uninitialized value warnings when accessing objcg fields. > + */ This explanation makes no sense to me. The kcalloc or kmalloc with __GFP_ZERO above has just cleared the object, and this is just clearing it again. It didn't happen sometimes in the past where KMSAN wouldn't track this. The bug must have a different explanation, such as getting an invalid pointer to kmem_cache_free(). Too bad it doesn't report any details about the address. > + if (vec) > + memset(vec, 0, objects * sizeof(*vec)); > + else { > /* > * Try to mark vectors which failed to allocate. > * If this operation fails, there may be a racing process