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Date: Mon, 02 Aug 2010 09:22:12 +0400 From: Dmitry Monakhov <dmonakhov@...nvz.org> To: Akira Fujita <a-fujita@...jp.nec.com> Cc: akpm@...ux-foundation.org, adilger@...ger.ca, Jan Kara <jack@...e.cz>, ext4 development <linux-ext4@...r.kernel.org> Subject: Re: BUG? ext3: Allocate blocks over quota limit with mmap Akira Fujita <a-fujita@...jp.nec.com> writes: > Hi ext3 maintainers, > > Could you look into this? > If this is not a problem, it is good though. Actually this is a problem. Because this issue makes quota just a fake limit. I've done this test for ext4 and was satisfied with result, but was too lazy to perform it on ext3/2 :( At least we have to have testcase for that in xfstest-qa. It seems that private page_mkwrite will be sufficient. I'm working on that. > > Regards, > Akira Fujita > > > (2010/07/29 11:08), Akira Fujita wrote: >> Hi, >> >> I found a problem that user can allocate blocks over quota limitation >> on ext3 (and ext2) with mmap. >> You can reproduce this with the following steps: >> >> 1. Enable user quota on ext3 >> [akira@...086 mnt]$ uname -r >> 2.6.35-rc6 >> >> [root@...086 mnt]# cat /proc/mounts | grep /dev/sda9 >> /dev/sda9 /mnt/mp1 ext3 rw,relatime,errors=continue,barrier=0,data=ordered,usrquota 0 0 >> >> [root@...086 mnt]# quotaon -p /mnt/mp1 >> group quota on /mnt/mp1 (/dev/sda9) is off >> user quota on /mnt/mp1 (/dev/sda9) is on >> >> [root@...086 mnt]# repquota -v /mnt/mp1 >> *** Report for user quotas on device /dev/sda9 >> Block grace time: 7days; Inode grace time: 7days >> Block limits File limits >> User used soft hard grace used soft hard grace >> ---------------------------------------------------------------------- >> root -- 1229 0 0 4 0 0 >> akira -- 0 100 1000 0 0 0 >> >> >> 2. Create sparse file on ext3 >> [akira@...086 mnt]$ df -T /mnt/mp1 >> Filesystem Type 1K-blocks Used Available Use% Mounted on >> /dev/sda9 ext3 23300 1236 20861 6% /mnt/mp1 >> >> [akira@...086 mnt]$ dd if=/dev/zero of=/mnt/mp1/file bs=4096 seek=1MB count=1 >> >> [akira@...086 mnt]$ ls -ls /mnt/mp1 >> total 26 >> 7 -rw------- 1 root root 7168 Jul 28 15:53 aquota.user >> 7 -rw-rw-r-- 1 akira akira 4096004096 Jul 28 15:53 file >> 12 drwx------ 2 root root 12288 Jul 28 14:49 lost+found >> >> [root@...086 mnt]# repquota -v /mnt/mp1 >> *** Report for user quotas on device /dev/sda9 >> Block grace time: 7days; Inode grace time: 7days >> Block limits File limits >> User used soft hard grace used soft hard grace >> ---------------------------------------------------------------------- >> root -- 1228 0 0 3 0 0 >> akira -- 8 100 1000 2 0 0 >> >> 3. Write data to "file" with mmap and msync. >> (In this time, write size is 50MB. It's larger than partition size ) >> e.g. >> long long contents = 0x0002; >> fd = (file, O_APPEND | O_RDWR, 0666); >> p = mmap(NULL, psize, PROT_WRITE, MAP_SHARED, fd, offset); >> memset(p, contents++, psize); >> offset += psize >> munmap(p, psize); >> close(fd); >> >> 4. Then run out disk space, user uses all of the blocks. >> [akira@...086 mnt]$ df -T /mnt/mp1 >> Filesystem Type 1K-blocks Used Available Use% Mounted on >> /dev/sda9 ext3 23300 23300 0 100% /mnt/mp1 >> ~~~~~ >> [root@...086 mnt]# repquota -v /mnt/mp1 >> *** Report for user quotas on device /dev/sda9 >> Block grace time: 7days; Inode grace time: 7days >> Block limits File limits >> User used soft hard grace used soft hard grace >> ---------------------------------------------------------------------- >> root -- 1228 0 0 3 0 0 >> akira +- 22065 100 1000 6days 2 0 0 >> ~~~~~ >> >> memset() after mmap() triggers the pagefault and then __do_fault >> marks whole pages correspond to offset we specified as dirty. >> After 5 seconds (or call sync), the kjournald tries to write out all of dirtied pages >> with getting blocks to disk. >> kjournald has CAP_SYS_RESOURCE capability, therefore it can ignore >> quota limitation (also can use blocks for root user). >> As a result, user can have blocks over quota limitation, >> though quota is enabled. >> Note: ext4 has own page_mkwrite, so this problem does not happen on it. >> >> I guess behavior of kjournald is correct (write out all dirty pages of file), >> so we need some consideration for pagefault behavior for ext3 and ext2. >> >> Is this a bug? >> >> Regards, >> Akira Fujita >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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