On Sat, 19 Jun 2021 at 11:26, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> When a lower file has sync/noatime fileattr flags, the behavior of
> overlayfs post copy up is inconsistent.
>
> Immediattely after copy up, ovl inode still has the S_SYNC/S_NOATIME
> inode flags copied from lower inode, so vfs code still treats the ovl
> inode as sync/noatime. After ovl inode evict or mount cycle,
> the ovl inode does not have these inode flags anymore.
>
> To fix this inconsitency, try to copy the fileattr flags on copy up
> if the upper fs supports the fileattr_set() method.
>
> This gives consistent behavior post copy up regardless of inode eviction
> from cache.
>
> We cannot copy up the immutable/append-only inode flags in a similar
> manner, because immutable/append-only inodes cannot be linked and because
> overlayfs will not be able to set overlay.* xattr on the upper inodes.
>
> Those flags will be addressed by a followup patch.
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/overlayfs/copy_up.c | 49 ++++++++++++++++++++++++++++++++++------
> fs/overlayfs/inode.c | 36 ++++++++++++++++++-----------
> fs/overlayfs/overlayfs.h | 14 +++++++++++-
> 3 files changed, 78 insertions(+), 21 deletions(-)
>
> diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> index 3fa68a5cc16e..a06b423ca5d1 100644
> --- a/fs/overlayfs/copy_up.c
> +++ b/fs/overlayfs/copy_up.c
> @@ -8,6 +8,7 @@
> #include <linux/fs.h>
> #include <linux/slab.h>
> #include <linux/file.h>
> +#include <linux/fileattr.h>
> #include <linux/splice.h>
> #include <linux/xattr.h>
> #include <linux/security.h>
> @@ -130,6 +131,31 @@ int ovl_copy_xattr(struct super_block *sb, struct dentry *old,
> return error;
> }
>
> +static int ovl_copy_fileattr(struct path *old, struct path *new)
> +{
> + struct fileattr oldfa = { .flags_valid = true };
> + struct fileattr newfa = { .flags_valid = true };
> + int err;
> +
> + err = ovl_real_fileattr(old, &oldfa, false);
> + if (err)
> + return err;
> +
> + err = ovl_real_fileattr(new, &newfa, false);
> + if (err)
> + return err;
> +
> + BUILD_BUG_ON(OVL_COPY_FS_FLAGS_MASK & ~FS_COMMON_FL);
> + newfa.flags &= ~OVL_COPY_FS_FLAGS_MASK;
> + newfa.flags |= (oldfa.flags & OVL_COPY_FS_FLAGS_MASK);
> +
> + BUILD_BUG_ON(OVL_COPY_FSX_FLAGS_MASK & ~FS_XFLAG_COMMON);
> + newfa.fsx_xflags &= ~OVL_COPY_FSX_FLAGS_MASK;
> + newfa.fsx_xflags |= (oldfa.fsx_xflags & OVL_COPY_FSX_FLAGS_MASK);
> +
> + return ovl_real_fileattr(new, &newfa, true);
> +}
> +
> static int ovl_copy_up_data(struct ovl_fs *ofs, struct path *old,
> struct path *new, loff_t len)
> {
> @@ -493,20 +519,21 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
> static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
> {
> struct ovl_fs *ofs = OVL_FS(c->dentry->d_sb);
> + struct inode *inode = d_inode(c->dentry);
> + struct path upperpath, datapath;
> int err;
>
> + ovl_path_upper(c->dentry, &upperpath);
> + if (WARN_ON(upperpath.dentry != NULL))
> + return -EIO;
> +
> + upperpath.dentry = temp;
> +
> /*
> * Copy up data first and then xattrs. Writing data after
> * xattrs will remove security.capability xattr automatically.
> */
> if (S_ISREG(c->stat.mode) && !c->metacopy) {
> - struct path upperpath, datapath;
> -
> - ovl_path_upper(c->dentry, &upperpath);
> - if (WARN_ON(upperpath.dentry != NULL))
> - return -EIO;
> - upperpath.dentry = temp;
> -
> ovl_path_lowerdata(c->dentry, &datapath);
> err = ovl_copy_up_data(ofs, &datapath, &upperpath,
> c->stat.size);
> @@ -518,6 +545,14 @@ static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
> if (err)
> return err;
>
> + if (inode->i_flags & OVL_COPY_I_FLAGS_MASK) {
> + /*
> + * Copy the fileattr inode flags that are the source of already
> + * copied i_flags (best effort).
> + */
> + ovl_copy_fileattr(&c->lowerpath, &upperpath);
I'm not sure this should be ignoring errors. Was this done to prevent
regressing cases where the upper fs cannot store the flags? Do you
have a concrete example?
Thanks,
Miklos
