From: NeilBrown neil@brown.name

nfsd exports a "pseudo root filesystem" which is used by NFSv4 to find the various exported filesystems using LOOKUP requests from a known root filehandle. NFSv3 uses the MOUNT protocol to find those exported filesystems and so is not given access to the pseudo root filesystem.

If a v3 (or v2) client uses a filehandle from that filesystem, nfsd_set_fh_dentry() will report an error, but still stores the export in "struct svc_fh" even though it also drops the reference (exp_put()). This means that when fh_put() is called an extra reference will be dropped which can lead to use-after-free and possible denial of service.

Normal NFS usage will not provide a pseudo-root filehandle to a v3 client. This bug can only be triggered by the client synthesising an incorrect filehandle.

To fix this we move the assignments to the svc_fh later, after all possible error cases have been detected.

Reported-and-tested-by: tianshuo han hantianshuo233@gmail.com Fixes: ef7f6c4904d0 ("nfsd: move V4ROOT version check to nfsd_set_fh_dentry()") Signed-off-by: NeilBrown neil@brown.name Reviewed-by: Jeff Layton jlayton@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Chuck Lever chuck.lever@oracle.com --- fs/nfsd/nfsfh.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c index 3eb724ec9566..ed85dd43da18 100644 --- a/fs/nfsd/nfsfh.c +++ b/fs/nfsd/nfsfh.c @@ -269,9 +269,6 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct net *net, dentry); }

- fhp->fh_dentry = dentry; - fhp->fh_export = exp; - switch (fhp->fh_maxsize) { case NFS4_FHSIZE: if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOATOMIC_ATTR) @@ -293,6 +290,9 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct net *net, goto out; }

+ fhp->fh_dentry = dentry; + fhp->fh_export = exp; + return 0; out: exp_put(exp);