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SubjectRe: NFSd: NULL-dereference when writing to v4_end_grace when server is not yet started
On Sun, Nov 25, 2018 at 09:17:10AM +0300, Anatoly Trosinenko wrote:
> When manually exploring the kernel NFSd feature, I have stumbled upon
> a NULL-dereference when writing to v4_end_grace when server is not yet
> started.

Thanks for the report!

I think this is what we want--it's what a lot of the other nfsctl
methods do.


commit ad5fdf47b4e3
Author: J. Bruce Fields <>
Date: Tue Nov 27 15:54:17 2018 -0500

nfsd4: fix crash on writing v4_end_grace before nfsd startup

Anatoly Trosinenko reports that this:

1) Checkout fresh master Linux branch (tested with commit e195ca6cb)
2) Copy x84_64-config-4.14 to .config, then enable NFS server v4 and build
3) From `kvm-xfstests shell`:

results in NULL dereference in locks_end_grace.

Check that nfsd has been started before trying to end the grace period.

Reported-by: Anatoly Trosinenko <>
Signed-off-by: J. Bruce Fields <>

diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 6384c9b94898..38b223c1378e 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -1126,7 +1126,13 @@ static ssize_t write_v4_end_grace(struct file *file, char *buf, size_t size)
case 'Y':
case 'y':
case '1':
+ mutex_lock(&nfsd_mutex);
+ if (nn->nfsd_serv) {
+ mutex_unlock(&nfsd_mutex);
+ return -EBUSY;
+ }
+ mutex_unlock(&nfsd_mutex);
return -EINVAL;
 \ /
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