Messages in this thread | | | Date | Wed, 11 May 2005 09:48:18 +0100 | From | Christoph Hellwig <> | Subject | Re: [RCF] [PATCH] unprivileged mount/umount |
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On Tue, May 03, 2005 at 04:31:35PM +0200, Miklos Szeredi wrote: > This (lightly tested) patch against 2.6.12-rc* adds some > infrastructure and basic functionality for unprivileged mount/umount > system calls.
Thanks for doing this.
> Details: > > - new mnt_owner field in struct vfsmount > - if mnt_owner is NULL, it's a privileged mount > - global limit on unprivileged mounts in /proc/sys/fs/mount-max
I think the name should be different. user-mount-max?
Acutally the accounting in your patch is a little odd, we account for all mounts, and after mount-max is reached user mounts are denied. Shouldn't we account only for user mounts?
> - per user limit of mounts in rlimit > - allow umount for the owner (except force flag) > - allow unprivileged bind mount to files/directories writable by owner > - add nosuid,nodev flags to unprivileged mounts > > Next step would be to add some policy for new mounts. I'm thinking of > either something static: e.g. FS_SAFE flag for "safe" filesystems, or > a more configurable approach through sysfs or something. > > Comments?
> --- a6d962c4f559f3644678574a66310084fd13d130/fs/namespace.c (mode:100644 sha1:3b93e5d750ebf8452ea1264251c5b55cc89f48f8) > +++ uncommitted/fs/namespace.c (mode:100644) > @@ -42,7 +42,7 @@ > static struct list_head *mount_hashtable; > static int hash_mask, hash_bits; > static kmem_cache_t *mnt_cache; > - > +struct mounts_stat_struct mounts_stat; > static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
minor nipick - please keep a empty line before the function here. Also I wonder whether we should have struct mounts_stat_struct at all, just having two variables seems a lot saner to me.
> - if (!capable(CAP_SYS_ADMIN)) > + if (!capable(CAP_SYS_ADMIN) && (nd.mnt->mnt_owner != current->user || > + (flags & MNT_FORCE))) > goto dput_and_out;
although it won't have different results I'd reorder this to make reading more easy:
if ((nd.mnt->mnt_owner != current->user || (flags & MNT_FORCE)) && !capable(CAP_SYS_ADMIN))
> -static int mount_is_safe(struct nameidata *nd) > +static struct user_struct *mount_is_safe(struct nameidata *nd) > { > if (capable(CAP_SYS_ADMIN)) > - return 0; > - return -EPERM; > -#ifdef notyet > - if (S_ISLNK(nd->dentry->d_inode->i_mode)) > - return -EPERM; > + return NULL; > + > + if (!S_ISDIR(nd->dentry->d_inode->i_mode) && > + !S_ISREG(nd->dentry->d_inode->i_mode)) > + return ERR_PTR(-EPERM); > if (nd->dentry->d_inode->i_mode & S_ISVTX) { > - if (current->uid != nd->dentry->d_inode->i_uid) > - return -EPERM; > + if (current->fsuid != nd->dentry->d_inode->i_uid) > + return ERR_PTR(-EPERM); > } > if (permission(nd->dentry->d_inode, MAY_WRITE, nd)) > - return -EPERM; > - return 0; > -#endif > + return ERR_PTR(-EPERM); > + return current->user;
Currently we do allow bind mounts over every type of file for the super user. I think we should keep allowing that. Also I think this function wants a really big comment explaining all the rules for user mounts.
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