[PATCH v1] NFSD: Return NFSERR_ISDIR for NFSv2 READ and WRITE on a non-regular file

[Chuck Lever <cel@kernel.org>]

Commit 0ac903d1bfdc ("NFS: NFSERR_INVAL is not defined by NFSv2")
changed the status NFSD returns for an NFSv2 READ or WRITE of a
symlink or other non-regular file from NFSERR_INVAL to NFSERR_IO.
RFC 1094 defines neither an INVAL nor a SYMLINK status.

U-Boot's NFS client follows a symlink only when READ fails with
NFSERR_ISDIR or NFSERR_INVAL. Since that commit it cannot load a
boot image through a symlink exported by a Linux NFS server: the
load completes with zero bytes transferred.

Solaris returns NFSERR_ISDIR when the target of an NFSv2 READ or
WRITE is not a regular file. Return the same status from NFSD.
Other NFSv2 procedures continue to return NFSERR_IO.

Fixes: 0ac903d1bfdc ("NFS: NFSERR_INVAL is not defined by NFSv2")
Reported-by: Jörg Sommer <joerg@jo-so.de>
Closes: https://lore.kernel.org/linux-nfs/apE90ZRZB8IW_AiS@jo-so.de/
Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfsproc.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index 48541ef7644f..09d360839825 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -40,6 +40,21 @@ static __be32 nfsd_map_status(__be32 status)
 	return status;
 }
 
+/*
+ * Because NFSv2 does not have an NFSERR_SYMLINK, Solaris returns
+ * NFSERR_ISDIR when the target of a READ or WRITE is any object
+ * that is not a regular file.
+ */
+static __be32 nfsd_map_io_status(__be32 status)
+{
+	switch (status) {
+	case nfserr_symlink:
+	case nfserr_wrong_type:
+		return nfserr_isdir;
+	}
+	return nfsd_map_status(status);
+}
+
 static __be32
 nfsd_proc_null(struct svc_rqst *rqstp)
 {
@@ -238,7 +253,7 @@ nfsd_proc_read(struct svc_rqst *rqstp)
 		resp->status = fh_getattr(&resp->fh, &resp->stat);
 	else if (resp->status == nfserr_jukebox)
 		set_bit(RQ_DROPME, &rqstp->rq_flags);
-	resp->status = nfsd_map_status(resp->status);
+	resp->status = nfsd_map_io_status(resp->status);
 	return rpc_success;
 }
 
@@ -271,7 +286,7 @@ nfsd_proc_write(struct svc_rqst *rqstp)
 		resp->status = fh_getattr(&resp->fh, &resp->stat);
 	else if (resp->status == nfserr_jukebox)
 		set_bit(RQ_DROPME, &rqstp->rq_flags);
-	resp->status = nfsd_map_status(resp->status);
+	resp->status = nfsd_map_io_status(resp->status);
 	return rpc_success;
 }
 
-- 
2.55.0