On Tue, May 05, 2020 at 11:59:12AM +0200, Miklos Szeredi wrote: > Determining whether a path or file descriptor refers to a mountpoint (or > more precisely a mount root) is not trivial using current tools. > > Add a flag to statx that indicates whether the path or fd refers to the > root of a mount or not. A brief summary of the previous discussion might be useful here. (Comparing st_dev is unreliable for bind mounts; openat2() with RESOLVE_NO_XDEV works for some use cases but triggers other code (like security checks and autofs) that are undesirable in other cases: https://lore.kernel.org/lkml/1450012.1585579399@xxxxxxxxxxxxxxxxxxxxxx/T/#ma4516eed1c7507b83343321e3ebd13bba972301c ) Looks good to me, though.--b. > > Reported-by: Lennart Poettering <mzxreary@xxxxxxxxxxx> > Reported-by: J. Bruce Fields <bfields@xxxxxxxxxxxx> > Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx> > --- > fs/stat.c | 3 +++ > include/uapi/linux/stat.h | 1 + > 2 files changed, 4 insertions(+) > > diff --git a/fs/stat.c b/fs/stat.c > index 3d88c99f7743..b9faa6cafafe 100644 > --- a/fs/stat.c > +++ b/fs/stat.c > @@ -202,6 +202,9 @@ int vfs_statx(int dfd, const char __user *filename, int flags, > error = vfs_getattr(&path, stat, request_mask, flags); > stat->mnt_id = real_mount(path.mnt)->mnt_id; > stat->result_mask |= STATX_MNT_ID; > + if (path.mnt->mnt_root == path.dentry) > + stat->attributes |= STATX_ATTR_MOUNT_ROOT; > + stat->attributes_mask |= STATX_ATTR_MOUNT_ROOT; > path_put(&path); > if (retry_estale(error, lookup_flags)) { > lookup_flags |= LOOKUP_REVAL; > diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h > index d81456247f10..6df9348bb277 100644 > --- a/include/uapi/linux/stat.h > +++ b/include/uapi/linux/stat.h > @@ -181,6 +181,7 @@ struct statx { > #define STATX_ATTR_NODUMP 0x00000040 /* [I] File is not to be dumped */ > #define STATX_ATTR_ENCRYPTED 0x00000800 /* [I] File requires key to decrypt in fs */ > #define STATX_ATTR_AUTOMOUNT 0x00001000 /* Dir: Automount trigger */ > +#define STATX_ATTR_MOUNT_ROOT 0x00002000 /* Root of a mount */ > #define STATX_ATTR_VERITY 0x00100000 /* [I] Verity protected file */ > > > -- > 2.21.1
