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Wed, 04 Dec 2024 23:05:56 -0800 (PST) Received: from google.com ([2401:fa00:8f:203:84f:5a2a:8b5d:f44f]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-215f8ef9dafsm5958855ad.120.2024.12.04.23.05.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Dec 2024 23:05:56 -0800 (PST) Date: Thu, 5 Dec 2024 16:05:52 +0900 From: Sergey Senozhatsky To: Andrew Morton , Kairui Song Cc: linux-mm@kvack.org, Minchan Kim , Sergey Senozhatsky , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Desheng Wu , stable@vger.kernel.org Subject: Re: [PATCH 1/2] zram: refuse to use zero sized block device as backing device Message-ID: <20241205070552.GE16709@google.com> References: <20241204180224.31069-1-ryncsn@gmail.com> <20241204180224.31069-2-ryncsn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241204180224.31069-2-ryncsn@gmail.com> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9074240002 X-Stat-Signature: 7aoawin79f48r1s16pugyc5czbtmzi7s X-Rspam-User: X-HE-Tag: 1733382339-884057 X-HE-Meta: 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 MzByLYO1 raJoLxgtFfEF15hhnupQABmb9IMa3uTGSQbYtBqhUwyIxFPaToxTHNLdTw0xDLa87/wr9sqnivbp4q1n6BDPB9kDpr60V2x9rZnjisrWMTIKOkrzaNmiEtmOwjCE6FbGRVFz9f54OxYCKDliuU3hsDQSM65X9F3fGGh7H+RJ+/cO+RLO8xf77pDl3f6ZNpoFIo5NAFGySVeZos9zmecZefhCjSzFJR+Ak/he3JRUUmjofKP+3pGd6jZgt46o9PP9gh2ysD7Nhjthx8M41ugcshvimSCUEfD8d/IUzJbiGJ2zIA/O978sf0xFAHj2wK/Jrv3VWKg+4GUPTfKarq5o/Pp0USN1ONrMqwsPbQVoU63PjwnZUbPQ/aQNOtfnH+ECu0LasigSM+zpB4/w= X-Bogosity: Ham, tests=bogofilter, spamicity=0.043300, 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 (24/12/05 02:02), Kairui Song wrote: > From: Kairui Song > > Setting a zero sized block device as backing device is pointless, and > one can easily create a recursive loop by setting the uninitialized > ZRAM device itself as its own backing device by (zram0 is uninitialized): > > echo /dev/zram0 > /sys/block/zram0/backing_dev > > It's definitely a wrong config, and the module will pin itself, > kernel should refuse doing so in the first place. > > By refusing to use zero sized device we avoided misuse cases > including this one above. > > Fixes: 013bf95a83ec ("zram: add interface to specif backing device") > Reported-by: Desheng Wu > Signed-off-by: Kairui Song > Cc: stable@vger.kernel.org Reviewed-by: Sergey Senozhatsky