On Mon, 4 Sept 2023 at 15:24, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > Some local filesystems support setting persistent fileattr flags > (e.g. FS_NOATIME_FL) on directories and regular files via ioctl. > Some of those persistent fileattr flags are reflected to vfs as > in-memory inode flags (e.g. S_NOATIME). > > Overlayfs uses the in-memory inode flags (e.g. S_NOATIME) on a lower file > as an indication that a the lower file may have persistent inode fileattr > flags (e.g. FS_NOATIME_FL) that need to be copied to upper file. > > However, in some cases, the S_NOATIME in-memory flag could be a false > indication for persistent FS_NOATIME_FL fileattr. For example, with NFS > and FUSE lower fs, as was the case in the two bug reports, the S_NOATIME > flag is set unconditionally for all inodes. > > Users cannot set persistent fileattr flags on symlinks and special files, > but in some local fs, such as ext4/btrfs/tmpfs, the FS_NOATIME_FL fileattr > flag are inheritted to symlinks and special files from parent directory. > > In both cases described above, when lower symlink has the S_NOATIME flag, > overlayfs will try to copy the symlink's fileattrs and fail with error > ENOXIO, because it could not open the symlink for the ioctl security hook. > > To solve this failure, do not attempt to copyup fileattrs for anything > other than directories and regular files. > > Reported-by: Ruiwen Zhao <ruiwen@xxxxxxxxxx> > Link: https://lore.kernel.org/r/CAKd=y5Hpg7J2gxrFT02F94o=FM9QvGp=kcH1Grctx8HzFYvpiA@xxxxxxxxxxxxxx/ > Fixes: 72db82115d2b ("ovl: copy up sync/noatime fileattr flags") > Cc: <stable@xxxxxxxxxxxxxxx> # v5.15 > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> > --- > > Hi Miklos, > > Do you agree with this solution? It's good enough. Linux might add API's in the future that allow querying and setting fileattr on symlinks, but we can deal with that later. Thanks, Miklos
