knfsd : export : Fix bug of svc_export_parse()

When I export /dev/null as root, and mount it from client, mount ntf4 command will frozen.

You can test it by following command:
#exportfs -i -o fsid=0,no_root_squash,insecure,rw,async *:/dev/null #mount -t nfs4 127.0.0.1:/ /tmp

This is because in svc_export_parse() function, if check_export return false, after we reject the file handle, we must do cleanup the cache, which is not a format error of file handle.

Signed-off-by Wei Yongjun <[email protected]>

nfsd/export.c renamed from nfsd/export.c.orig +0 -3

@@ -543,12 +543,13 @@ static int svc_export_parse(struct cache
 		if (err) goto out;
 		exp.ex_fsid = an_int;
 
-		err = check_export(nd.dentry->d_inode, exp.ex_flags);
-		if (err) goto out;
-

Nobody replied yet, but I think this is really a BUG of exportfs. exportfs command does not check so strictly, so maybe some unreasonable fh.key can be add to /proc/net/rpc/nfsd.fh/channel, but used this key to find fh.handle, this always be fail and still retry.

It's this correct?

Quoted 7 lines · On Tuesday March 27, [email protected] wrote:

Nobody replied yet, but I think this is really a BUG of exportfs. exportfs command does not check so strictly, so maybe some unreasonable fh.key can be add to /proc/net/rpc/nfsd.fh/channel, but used this key to find fh.handle, this always be fail and still retry.

It's this correct?

Sorry for not replying earlier.

Yes, you have identified a real problem, but I'm not sure I agree with the first.

If someone (mountd) tried to tell the kernel to export "/dev/null", it fails with an error (-ENODIR), and I think this is correct.

Mountd should respond properly to this error, which it doesn't at the moment.
When the request comes via the MOUNT protocol from an NFSv2 or NFSv3 client, mountd will fail the mount as it should.
However when the request comes from the kernel due to an NFSv4 request, the error is just ignored. In that case we really should be telling the kernel that the filehandle is not valid by writing out an appropriate message.

Maybe something like this in nfs-utils.
What do you think?

Signed-off-by Neil Brown <[email protected]>

### Diffstat output

 ./utils/mountd/cache.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff .prev/utils/mountd/cache.c ./utils/mountd/cache.c

utils/mountd/cache.c +2 -1

@@ -469,7 +469,8 @@ void nfsd_fh(FILE *f)
 	}
 
 	if (found)
-		cache_export_ent(dom, found, found_path);
+		if (cache_export_ent(dom, found, found_path) < 0)
+			found = 0;
 
 	qword_print(f, dom);
 	qword_printint(f, fsidtype);

@@ -619,8 +620,10 @@ void nfsd_export(FILE *f)
 	}