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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-66faa62c132sm753177d50.7.2026.09.02.19.31.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2026 19:31:57 -0700 (PDT) Date: Wed, 2 Sep 2026 19:31:39 -0700 (PDT) From: Hugh Dickins To: Jan Kara cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, ocfs2-devel@lists.linux.dev, Joseph Qi , Hugh Dickins , Baolin Wang , Farhad Alemi Subject: Re: [PATCH 2/2] shmem: Refuse to enable tmpfs format for another filesystem In-Reply-To: <20260902133702.1313635-4-jack@suse.cz> Message-ID: <5f7e2e81-6a79-3b5a-1dc2-83ce775017ac@google.com> References: <20260902132458.23590-1-jack@suse.cz> <20260902133702.1313635-4-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 683A614000B X-Stat-Signature: a6nrg14pgr8o7ra5m63mrridt3narrk9 X-Rspam-User: X-HE-Tag: 1788402720-753948 X-HE-Meta: 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 3D1CYoky HtICx7qyJihTRmrVVy94PdBevU57Cgvdh3q9TQwnYiz93bKP5XUhpt1iJTIX2uxhbUrWc2dIdKAnxYN9OTIvoAT+wm2/JyoyLheCG4/9sotAErFM7wbmBsjmlqtLJZaei0+DD71n4lbUV1a1KtptZYeRSgV7Vo8hCrSz+I7qrFfX8tjoN2rLj4BJZ+fOn4xzOF3yx/mLkf1PJcazU/ApCBrfXsG77YZD2B7OS/swInPmkwaiEPA5ZB018jfOhUh/9Q537Rcs42EigTsD1O/neo8jCgGiEREJ37JnbIK0TeKcEbGFryipxwBaVVgg3UitzxYJm58aai4P6Vbc4HGrtv4KRh6PKC/iV0kSxu5YKSk3werA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 2 Sep 2026, Jan Kara wrote: > It is possible to issue Q_QUOTAON quotactl(2) e.g. for ext4 filesystem > requesting to enable quota using tmpfs quota format. With suitable > passed arguments this can actually succeed in enabling tmpfs quota > format on top of ext4 filesystem which leads to crashes later in > dquot_acquire(). As tmpfs quota format is intended for tmpfs > filesystems only, verify we are indeed enabling quotas there. > > Reported-by: Farhad Alemi > Signed-off-by: Jan Kara > --- > mm/shmem_quota.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/shmem_quota.c b/mm/shmem_quota.c > index d0b92d6da50f..6e0b43cbded3 100644 > --- a/mm/shmem_quota.c > +++ b/mm/shmem_quota.c > @@ -54,6 +54,10 @@ struct quota_id { > > static int shmem_check_quota_file(struct super_block *sb, int type) > { > + /* Verify enabling happens on tmpfs superblock */ > + if (strcmp(sb->s_type->name, "tmpfs")) > + return 0; > + I don't object to this, but was rather expecting you'd check s_magic for TMPFS_MAGIC: isn't this the kind of hi-tech thing s_magic is for? Thanks anyway, Hugh > /* There is no real quota file, nothing to do */ > return 1; > } > -- > 2.51.0