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Tue, 22 Sep 2026 05:17:40 -0700 (PDT) Received: from Raccoon ([2409:408d:3188:aa03:3bb2:acc7:b581:620]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-144f2a44cc8sm4892510c88.13.2026.09.22.05.17.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2026 05:17:39 -0700 (PDT) From: Rohinthan To: Minchan Kim , Sergey Senozhatsky , Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Rohinthan , syzbot+fb23651a7efbea8868ed@syzkaller.appspotmail.com Subject: [PATCH] zram: reject zero or overflowed disksize in disksize_store Date: Tue, 22 Sep 2026 17:47:20 +0530 Message-ID: <20260922121720.11241-1-rokinthanp03@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When userspace writes a value close to U64_MAX (such as (u64)-1) to the sysfs attribute /sys/block/zram/disksize, disksize_store() parses it with memparse() and then calls: disksize = PAGE_ALIGN(disksize); Because adding PAGE_SIZE - 1 to values in the range [U64_MAX - PAGE_SIZE + 2, U64_MAX] causes an integer overflow wrapping to 0, disksize becomes 0. disksize_store() then passes 0 to zram_meta_alloc(), which computes num_pages = 0 and calls vzalloc(0). In mm/vmalloc.c, __vmalloc_node_range_noprof() checks `if (WARN_ON_ONCE(!size))` and triggers a kernel warning: WARNING: mm/vmalloc.c:4038 at __vmalloc_node_range_noprof Call trace: __vmalloc_node_range_noprof vzalloc_noprof disksize_store dev_attr_store sysfs_kf_write Fix this by checking if disksize wrapped to 0 after PAGE_ALIGN(disksize) and returning -EINVAL. Also add a defensive check in zram_meta_alloc() to return false if disksize is 0, avoiding vzalloc(0) under any circumstance. Fixes: cd67e10ac699 ("zram: promote zram from staging") Reported-by: syzbot+fb23651a7efbea8868ed@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=fb23651a7efbea8868ed Signed-off-by: Rohinthan --- drivers/block/zram/zram_drv.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 6cb44e2..fdd13df 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1989,6 +1989,9 @@ static bool zram_meta_alloc(struct zram *zram, u64 disksize) { size_t num_pages; + if (!disksize) + return false; + num_pages = disksize >> PAGE_SHIFT; zram->table = vzalloc(array_size(num_pages, sizeof(*zram->table))); if (!zram->table) @@ -2878,6 +2881,9 @@ static ssize_t disksize_store(struct device *dev, struct device_attribute *attr, } disksize = PAGE_ALIGN(disksize); + if (!disksize) + return -EINVAL; + if (!zram_meta_alloc(zram, disksize)) return -ENOMEM; -- 2.53.0