pidfs and nsfs recently gained support for encode/decode of file handles via name_to_handle_at(2)/opan_by_handle_at(2). These special kernel filesystems have custom ->open() and ->permission() export methods, which nfsd does not respect and it was never meant to be used for exporting those filesystems by nfsd. Update kernel-doc comments to express the fact the those methods are for open_by_handle(2) system only and not compatible with nfsd. Signed-off-by: Amir Goldstein --- include/linux/exportfs.h | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h index 262e24d833134..fafd22ed4c648 100644 --- a/include/linux/exportfs.h +++ b/include/linux/exportfs.h @@ -192,7 +192,9 @@ struct handle_to_path_ctx { #define FILEID_VALID_USER_FLAGS (FILEID_IS_CONNECTABLE | FILEID_IS_DIR) /** - * struct export_operations - for nfsd to communicate with file systems + * struct export_operations + * + * Methods for nfsd to communicate with file systems: * @encode_fh: encode a file handle fragment from a dentry * @fh_to_dentry: find the implied object and get a dentry for it * @fh_to_parent: find the implied object's parent and get a dentry for it @@ -200,6 +202,10 @@ struct handle_to_path_ctx { * @get_parent: find the parent of a given directory * @commit_metadata: commit metadata changes to stable storage * + * Methods for open_by_handle(2) syscall with special kernel file systems: + * @permission: custom permission for opening a file by handle + * @open: custom open routine for opening file by handle + * * See Documentation/filesystems/nfs/exporting.rst for details on how to use * this interface correctly and the definition of the flags. * @@ -244,10 +250,14 @@ struct handle_to_path_ctx { * space cannot be allocated, a %ERR_PTR should be returned. * * @permission: - * Allow filesystems to specify a custom permission function. + * Allow filesystems to specify a custom permission function for the + * open_by_handle_at(2) syscall instead of the default permission check. + * This custom permission function is not respected by nfsd. * * @open: - * Allow filesystems to specify a custom open function. + * Allow filesystems to specify a custom open function for the + * open_by_handle_at(2) syscall instead of the default file_open_root(). + * This custom open function is not respected by nfsd. * * @commit_metadata: * @commit_metadata should commit metadata changes to stable storage. -- 2.52.0 pidfs and nsfs recently gained support for encode/decode of file handles via name_to_handle_at(2)/opan_by_handle_at(2). These special kernel filesystems have custom ->open() and ->permission() export methods, which nfsd does not respect and it was never meant to be used for exporting those filesystems by nfsd. Therefore, do not allow nfsd to export filesystems with custom ->open() or ->permission() methods. Fixes: b3caba8f7a34a ("pidfs: implement file handle support") Fixes: 5222470b2fbb3 ("nsfs: support file handles") Signed-off-by: Amir Goldstein --- fs/nfsd/export.c | 8 +++++--- include/linux/exportfs.h | 9 +++++++++ 2 files changed, 14 insertions(+), 3 deletions(-) diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c index 2a1499f2ad196..09fe268fe2c76 100644 --- a/fs/nfsd/export.c +++ b/fs/nfsd/export.c @@ -427,7 +427,8 @@ static int check_export(const struct path *path, int *flags, unsigned char *uuid * either a device number (so FS_REQUIRES_DEV needed) * or an FSID number (so NFSEXP_FSID or ->uuid is needed). * 2: We must be able to find an inode from a filehandle. - * This means that s_export_op must be set. + * This means that s_export_op must be set and comply with + * the requirements for remote filesystem export. * 3: We must not currently be on an idmapped mount. */ if (!(inode->i_sb->s_type->fs_flags & FS_REQUIRES_DEV) && @@ -437,8 +438,9 @@ static int check_export(const struct path *path, int *flags, unsigned char *uuid return -EINVAL; } - if (!exportfs_can_decode_fh(inode->i_sb->s_export_op)) { - dprintk("exp_export: export of invalid fs type.\n"); + if (!exportfs_may_export(inode->i_sb->s_export_op)) { + dprintk("exp_export: export of invalid fs type (%s).\n", + inode->i_sb->s_type->name); return -EINVAL; } diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h index fafd22ed4c648..bf3dee2ad5f97 100644 --- a/include/linux/exportfs.h +++ b/include/linux/exportfs.h @@ -340,6 +340,15 @@ static inline bool exportfs_can_decode_fh(const struct export_operations *nop) return nop && nop->fh_to_dentry; } +static inline bool exportfs_may_export(const struct export_operations *nop) +{ + /* + * Do not allow nfs export for filesystems with custom ->open() and + * ->permission() ops, which nfsd does not respect (e.g. pidfs, nsfs). + */ + return exportfs_can_decode_fh(nop) && !nop->open && !nop->permission; +} + static inline bool exportfs_can_encode_fh(const struct export_operations *nop, int fh_flags) { -- 2.52.0