On Wed, Aug 15, 2012 at 5:48 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote: > From: Miklos Szeredi <mszeredi@xxxxxxx> > > Add a simple read-only counter to super_block that indicates deep this > is in the stack of filesystems. Previously ecryptfs was the only > stackable filesystem and it explicitly disallowed multiple layers of > itself. > > Overlayfs, however, can be stacked recursively and also may be stacked > on top of ecryptfs or vice versa. > > To limit the kernel stack usage we must limit the depth of the > filesystem stack. Initially the limit is set to 2. > Hi, I have tested OverlayFS for a long time with "fs-stack-depth=3". The original OverlayFS test-case script from Jordi was slightly modified (see "testcase-ovl-v3.sh"). I have sent my test-results to Andy and Jordi (tested with the patchset from Andy against Linux-v3.4 [1] with Ext4-FS). The attached test-case script *requires* "fs-stack-depth=3" to run properly (patch attached). So, I have 2 questions: [1] FS-stack-limitation Is a "fs-stack-depth>=2" (like "3") critical? Is your setting to "2" just a defensive (and initial) one? Can you explain your choice a bit more as ecryptFS is involved in this limitation, too. [2] Test-Case/Use-Case scripts It would be *very very very* helpful if you could provide or even ship in the Linux-kernel a test-case/use-case script, Thanks! Maybe describe "Documentation/filesystems/overlayfs.txt" would be a good place? Helpful could be a "simple" and a "complex" testing scenario? - Sedat - [1] http://git.kernel.org/?p=linux/kernel/git/apw/overlayfs.git;a=shortlog;h=refs/heads/overlayfs.v12apw1 > Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx> > --- > fs/ecryptfs/main.c | 7 +++++++ > fs/overlayfs/super.c | 10 ++++++++++ > include/linux/fs.h | 11 +++++++++++ > 3 files changed, 28 insertions(+), 0 deletions(-) > > diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c > index 2768138..344fb2c 100644 > --- a/fs/ecryptfs/main.c > +++ b/fs/ecryptfs/main.c > @@ -565,6 +565,13 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags > s->s_maxbytes = path.dentry->d_sb->s_maxbytes; > s->s_blocksize = path.dentry->d_sb->s_blocksize; > s->s_magic = ECRYPTFS_SUPER_MAGIC; > + s->s_stack_depth = path.dentry->d_sb->s_stack_depth + 1; > + > + rc = -EINVAL; > + if (s->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) { > + printk(KERN_ERR "eCryptfs: maximum fs stacking depth exceeded\n"); > + goto out_free; > + } > > inode = ecryptfs_get_inode(path.dentry->d_inode, s); > rc = PTR_ERR(inode); > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c > index 69a2099..64d2695 100644 > --- a/fs/overlayfs/super.c > +++ b/fs/overlayfs/super.c > @@ -551,6 +551,16 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) > !S_ISDIR(lowerpath.dentry->d_inode->i_mode)) > goto out_put_lowerpath; > > + sb->s_stack_depth = max(upperpath.mnt->mnt_sb->s_stack_depth, > + lowerpath.mnt->mnt_sb->s_stack_depth) + 1; > + > + err = -EINVAL; > + if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) { > + printk(KERN_ERR "overlayfs: maximum fs stacking depth exceeded\n"); > + goto out_put_lowerpath; > + } > + > + > ufs->upper_mnt = clone_private_mount(&upperpath); > err = PTR_ERR(ufs->upper_mnt); > if (IS_ERR(ufs->upper_mnt)) { > diff --git a/include/linux/fs.h b/include/linux/fs.h > index abc7a53..1265e24 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -505,6 +505,12 @@ struct iattr { > */ > #include <linux/quota.h> > > +/* > + * Maximum number of layers of fs stack. Needs to be limited to > + * prevent kernel stack overflow > + */ > +#define FILESYSTEM_MAX_STACK_DEPTH 2 > + > /** > * enum positive_aop_returns - aop return codes with specific semantics > * > @@ -1579,6 +1585,11 @@ struct super_block { > > /* Being remounted read-only */ > int s_readonly_remount; > + > + /* > + * Indicates how deep in a filesystem stack this SB is > + */ > + int s_stack_depth; > }; > > /* superblock cache pruning functions */ > -- > 1.7.7 >
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testcase-ovl-v3.sh
Description: Bourne shell script
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0001-fs-Increase-limit-filesystem-stacking-depth-to-3.patch
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