From: Vivek Goyal <vgoyal@redhat.com> To: Theodore Ts'o <tytso@mit.edu> Cc: Daniel Walsh <dwalsh@redhat.com>, Casey Schaufler <casey@schaufler-ca.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, "Schaufler, Casey" <casey.schaufler@intel.com>, "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>, "virtio-fs@redhat.com" <virtio-fs@redhat.com>, "berrange@redhat.com" <berrange@redhat.com>, linux-security-module <linux-security-module@vger.kernel.org>, "selinux@vger.kernel.org" <selinux@vger.kernel.org> Subject: Re: [RFC PATCH 0/1] xattr: Allow user.* xattr on symlink/special files if caller has CAP_SYS_RESOURCE Date: Wed, 30 Jun 2021 10:27:15 -0400 [thread overview] Message-ID: <20210630142715.GB75386@redhat.com> (raw) In-Reply-To: <YNvvLIv16jY8mfP8@mit.edu> On Wed, Jun 30, 2021 at 12:12:28AM -0400, Theodore Ts'o wrote: > On Tue, Jun 29, 2021 at 04:28:24PM -0400, Daniel Walsh wrote: > > All this conversation is great, and I look forward to a better solution, but > > if we go back to the patch, it was to fix an issue where the kernel is > > requiring CAP_SYS_ADMIN for writing user Xattrs on link files and other > > special files. > > > > The documented reason for this is to prevent the users from using XATTRS to > > avoid quota. > > Huh? Where is it so documented? Its in "man xattr". David already copied pasted the relevant section in another email, so I am not doing it. > How file systems store and account > for space used by extended attributes is a file-system specific > question, > but presumably any way that xattr's on regular files are > accounted could also be used for xattr's on special files. That will be nice. I don't know enough about quota, but I am wondering why quota limits can't be enforced (if needed) for symlinks and special file xattrs. Thanks Vivek > > Also, xattr's are limited to 32k, so it's not like users can evade > _that_ much quota space, at least not without it being pretty painful. > (Assuming that quota is even enabled, which most of the time, it > isn't.) > > - Ted > > P.S. I'll note that if ext4's ea_in_inode is enabled, for large > xattr's, if you have 2 million files that all have the same 12k > windows SID stored as an xattr, ext4 will store that xattr only once. > Those two million files might be owned by different uids, so we made > an explicit design choice not to worry about accounting for the quota > for said 12k xattr value. After all, if you can save the space and > access cost of 2M * 12k if each file had to store its own copy of that > xattr, perhaps not including it in the quota calculation isn't that > bad. :-) > > We also don't account for the disk space used by symbolic links (since > sometimes they can be stored in the inode as fast symlinks, and > sometimes they might consume a data block). But again, that's a file > system specific implementation question. >
WARNING: multiple messages have this Message-ID (diff)
From: Vivek Goyal <vgoyal@redhat.com> To: Theodore Ts'o <tytso@mit.edu> Cc: "berrange@redhat.com" <berrange@redhat.com>, "selinux@vger.kernel.org" <selinux@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "virtio-fs@redhat.com" <virtio-fs@redhat.com>, "Schaufler, Casey" <casey.schaufler@intel.com>, linux-security-module <linux-security-module@vger.kernel.org>, "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>, Casey Schaufler <casey@schaufler-ca.com>, "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org> Subject: Re: [Virtio-fs] [RFC PATCH 0/1] xattr: Allow user.* xattr on symlink/special files if caller has CAP_SYS_RESOURCE Date: Wed, 30 Jun 2021 10:27:15 -0400 [thread overview] Message-ID: <20210630142715.GB75386@redhat.com> (raw) In-Reply-To: <YNvvLIv16jY8mfP8@mit.edu> On Wed, Jun 30, 2021 at 12:12:28AM -0400, Theodore Ts'o wrote: > On Tue, Jun 29, 2021 at 04:28:24PM -0400, Daniel Walsh wrote: > > All this conversation is great, and I look forward to a better solution, but > > if we go back to the patch, it was to fix an issue where the kernel is > > requiring CAP_SYS_ADMIN for writing user Xattrs on link files and other > > special files. > > > > The documented reason for this is to prevent the users from using XATTRS to > > avoid quota. > > Huh? Where is it so documented? Its in "man xattr". David already copied pasted the relevant section in another email, so I am not doing it. > How file systems store and account > for space used by extended attributes is a file-system specific > question, > but presumably any way that xattr's on regular files are > accounted could also be used for xattr's on special files. That will be nice. I don't know enough about quota, but I am wondering why quota limits can't be enforced (if needed) for symlinks and special file xattrs. Thanks Vivek > > Also, xattr's are limited to 32k, so it's not like users can evade > _that_ much quota space, at least not without it being pretty painful. > (Assuming that quota is even enabled, which most of the time, it > isn't.) > > - Ted > > P.S. I'll note that if ext4's ea_in_inode is enabled, for large > xattr's, if you have 2 million files that all have the same 12k > windows SID stored as an xattr, ext4 will store that xattr only once. > Those two million files might be owned by different uids, so we made > an explicit design choice not to worry about accounting for the quota > for said 12k xattr value. After all, if you can save the space and > access cost of 2M * 12k if each file had to store its own copy of that > xattr, perhaps not including it in the quota calculation isn't that > bad. :-) > > We also don't account for the disk space used by symbolic links (since > sometimes they can be stored in the inode as fast symlinks, and > sometimes they might consume a data block). But again, that's a file > system specific implementation question. >
next prev parent reply other threads:[~2021-06-30 14:27 UTC|newest] Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-25 19:12 [RFC PATCH 0/1] xattr: Allow user.* xattr on symlink/special files if caller has CAP_SYS_RESOURCE Vivek Goyal 2021-06-25 19:12 ` [Virtio-fs] " Vivek Goyal 2021-06-25 19:12 ` [PATCH 1/1] xattr: Allow user.* xattr on symlink/special files with CAP_SYS_RESOURCE Vivek Goyal 2021-06-25 19:12 ` [Virtio-fs] " Vivek Goyal 2021-06-28 12:33 ` Christian Brauner 2021-06-28 12:33 ` [Virtio-fs] " Christian Brauner 2021-06-28 15:00 ` Vivek Goyal 2021-06-28 15:00 ` [Virtio-fs] " Vivek Goyal 2021-06-29 3:13 ` [xattr] 8d8cd767b6: ltp.setxattr02.fail kernel test robot 2021-06-29 3:13 ` [Virtio-fs] " kernel test robot 2021-06-29 3:13 ` kernel test robot 2021-06-29 3:13 ` [LTP] " kernel test robot 2021-06-29 12:59 ` Vivek Goyal 2021-06-29 12:59 ` [Virtio-fs] " Vivek Goyal 2021-06-29 12:59 ` Vivek Goyal 2021-06-29 12:59 ` [LTP] " Vivek Goyal 2021-06-25 21:49 ` [RFC PATCH 0/1] xattr: Allow user.* xattr on symlink/special files if caller has CAP_SYS_RESOURCE Schaufler, Casey 2021-06-25 21:49 ` [Virtio-fs] " Schaufler, Casey 2021-06-28 11:58 ` Dr. David Alan Gilbert 2021-06-28 11:58 ` [Virtio-fs] " Dr. David Alan Gilbert 2021-06-28 13:17 ` Vivek Goyal 2021-06-28 13:17 ` [Virtio-fs] " Vivek Goyal 2021-06-28 13:36 ` Daniel Walsh 2021-06-28 13:36 ` [Virtio-fs] " Daniel Walsh 2021-06-28 16:04 ` Casey Schaufler 2021-06-28 16:04 ` [Virtio-fs] " Casey Schaufler 2021-06-28 16:28 ` Dr. David Alan Gilbert 2021-06-28 16:28 ` [Virtio-fs] " Dr. David Alan Gilbert 2021-06-28 17:41 ` Casey Schaufler 2021-06-28 17:41 ` [Virtio-fs] " Casey Schaufler 2021-06-29 9:00 ` Dr. David Alan Gilbert 2021-06-29 9:00 ` [Virtio-fs] " Dr. David Alan Gilbert 2021-06-29 14:38 ` Casey Schaufler 2021-06-29 14:38 ` [Virtio-fs] " Casey Schaufler 2021-06-29 15:20 ` Vivek Goyal 2021-06-29 15:20 ` [Virtio-fs] " Vivek Goyal 2021-06-29 16:13 ` Casey Schaufler 2021-06-29 16:13 ` [Virtio-fs] " Casey Schaufler 2021-06-29 16:35 ` Dr. David Alan Gilbert 2021-06-29 16:35 ` [Virtio-fs] " Dr. David Alan Gilbert 2021-06-29 16:51 ` Casey Schaufler 2021-06-29 16:51 ` [Virtio-fs] " Casey Schaufler 2021-06-29 17:35 ` Vivek Goyal 2021-06-29 17:35 ` [Virtio-fs] " Vivek Goyal 2021-06-29 20:28 ` Daniel Walsh 2021-06-29 20:28 ` [Virtio-fs] " Daniel Walsh 2021-06-30 4:12 ` Theodore Ts'o 2021-06-30 4:12 ` [Virtio-fs] " Theodore Ts'o 2021-06-30 8:07 ` Dr. David Alan Gilbert 2021-06-30 8:07 ` [Virtio-fs] " Dr. David Alan Gilbert 2021-06-30 14:47 ` Theodore Ts'o 2021-06-30 14:47 ` [Virtio-fs] " Theodore Ts'o 2021-06-30 15:01 ` Dr. David Alan Gilbert 2021-06-30 15:01 ` [Virtio-fs] " Dr. David Alan Gilbert 2021-06-30 19:59 ` Theodore Ts'o 2021-06-30 19:59 ` [Virtio-fs] " Theodore Ts'o 2021-06-30 20:32 ` Vivek Goyal 2021-06-30 20:32 ` [Virtio-fs] " Vivek Goyal 2021-07-01 8:48 ` Dr. David Alan Gilbert 2021-07-01 8:48 ` [Virtio-fs] " Dr. David Alan Gilbert 2021-07-01 12:21 ` Vivek Goyal 2021-07-01 12:21 ` [Virtio-fs] " Vivek Goyal 2021-07-01 13:10 ` Vivek Goyal 2021-07-01 13:10 ` [Virtio-fs] " Vivek Goyal 2021-07-01 16:58 ` Casey Schaufler 2021-07-01 16:58 ` [Virtio-fs] " Casey Schaufler 2021-06-30 16:09 ` Vivek Goyal 2021-06-30 16:09 ` [Virtio-fs] " Vivek Goyal 2021-06-30 14:27 ` Vivek Goyal [this message] 2021-06-30 14:27 ` Vivek Goyal 2021-06-29 16:25 ` Theodore Ts'o 2021-06-29 16:25 ` [Virtio-fs] " Theodore Ts'o 2021-06-28 17:22 ` Vivek Goyal 2021-06-28 17:22 ` [Virtio-fs] " Vivek Goyal 2021-06-28 18:55 ` Daniel Walsh 2021-06-28 18:55 ` [Virtio-fs] " Daniel Walsh
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