Re: [PATCH] nfsd: zero out umask if the client didn't provide one

["J . Bruce Fields" <bfields@fieldses.org>]

This is what I'm planning to apply (pending some testing).

--b.

commit 880a3a532548
Author: J. Bruce Fields <bfields@redhat.com>
Date:   Wed Mar 21 17:19:02 2018 -0400

    nfsd: fix incorrect umasks
    
    We're neglecting to clear the umask after it's set, which can cause a
    later unrelated rpc to (incorrectly) use the same umask if it happens to
    be processed by the same thread.
    
    There's a more subtle problem here too:
    
    An NFSv4 compound request is decoded all in one pass before any
    operations are executed.
    
    Currently we're setting current->fs->umask at the time we decode the
    compound.  In theory a single compound could contain multiple creates
    each setting a umask.  In that case we'd end up using whichever umask
    was passed in the *last* operation as the umask for all the creates,
    whether that was correct or not.
    
    So, we should just be saving the umask at decode time and waiting to set
    it until we actually process the corresponding operation.
    
    In practice it's unlikely any client would do multiple creates in a
    single compound.  And even if it did they'd likely be from the same
    process (hence carry the same umask).  So this is a little academic, but
    we should get it right anyway.
    
    Fixes: 47057abde515 (nfsd: add support for the umask attribute)
    Cc: stable@vger.kernel.org
    Reported-by: Lucash Stach <l.stach@pengutronix.de>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index c6157ece46b1..5d99e8810b85 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -32,6 +32,7 @@
  *  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
+#include <linux/fs_struct.h>
 #include <linux/file.h>
 #include <linux/falloc.h>
 #include <linux/slab.h>
@@ -252,11 +253,13 @@ do_open_lookup(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, stru
 		 * Note: create modes (UNCHECKED,GUARDED...) are the same
 		 * in NFSv4 as in v3 except EXCLUSIVE4_1.
 		 */
+		current->fs->umask = open->op_umask;
 		status = do_nfsd_create(rqstp, current_fh, open->op_fname.data,
 					open->op_fname.len, &open->op_iattr,
 					*resfh, open->op_createmode,
 					(u32 *)open->op_verf.data,
 					&open->op_truncate, &open->op_created);
+		current->fs->umask = 0;
 
 		if (!status && open->op_label.len)
 			nfsd4_security_inode_setsecctx(*resfh, &open->op_label, open->op_bmval);
@@ -603,6 +606,7 @@ nfsd4_create(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	if (status)
 		return status;
 
+	current->fs->umask = create->cr_umask;
 	switch (create->cr_type) {
 	case NF4LNK:
 		status = nfsd_symlink(rqstp, &cstate->current_fh,
@@ -611,20 +615,22 @@ nfsd4_create(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 		break;
 
 	case NF4BLK:
+		status = nfserr_inval;
 		rdev = MKDEV(create->cr_specdata1, create->cr_specdata2);
 		if (MAJOR(rdev) != create->cr_specdata1 ||
 		    MINOR(rdev) != create->cr_specdata2)
-			return nfserr_inval;
+			goto out_umask;
 		status = nfsd_create(rqstp, &cstate->current_fh,
 				     create->cr_name, create->cr_namelen,
 				     &create->cr_iattr, S_IFBLK, rdev, &resfh);
 		break;
 
 	case NF4CHR:
+		status = nfserr_inval;
 		rdev = MKDEV(create->cr_specdata1, create->cr_specdata2);
 		if (MAJOR(rdev) != create->cr_specdata1 ||
 		    MINOR(rdev) != create->cr_specdata2)
-			return nfserr_inval;
+			goto out_umask;
 		status = nfsd_create(rqstp, &cstate->current_fh,
 				     create->cr_name, create->cr_namelen,
 				     &create->cr_iattr,S_IFCHR, rdev, &resfh);
@@ -668,6 +674,8 @@ nfsd4_create(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	fh_dup2(&cstate->current_fh, &resfh);
 out:
 	fh_put(&resfh);
+out_umask:
+	current->fs->umask = 0;
 	return status;
 }
 
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index dd72cdf3662e..1d048dd95464 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -33,7 +33,6 @@
  *  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <linux/fs_struct.h>
 #include <linux/file.h>
 #include <linux/slab.h>
 #include <linux/namei.h>
@@ -682,7 +681,7 @@ nfsd4_decode_create(struct nfsd4_compoundargs *argp, struct nfsd4_create *create
 
 	status = nfsd4_decode_fattr(argp, create->cr_bmval, &create->cr_iattr,
 				    &create->cr_acl, &create->cr_label,
-				    &current->fs->umask);
+				    &create->cr_umask);
 	if (status)
 		goto out;
 
@@ -927,7 +926,6 @@ nfsd4_decode_open(struct nfsd4_compoundargs *argp, struct nfsd4_open *open)
 	case NFS4_OPEN_NOCREATE:
 		break;
 	case NFS4_OPEN_CREATE:
-		current->fs->umask = 0;
 		READ_BUF(4);
 		open->op_createmode = be32_to_cpup(p++);
 		switch (open->op_createmode) {
@@ -935,7 +933,7 @@ nfsd4_decode_open(struct nfsd4_compoundargs *argp, struct nfsd4_open *open)
 		case NFS4_CREATE_GUARDED:
 			status = nfsd4_decode_fattr(argp, open->op_bmval,
 				&open->op_iattr, &open->op_acl, &open->op_label,
-				&current->fs->umask);
+				&open->op_umask);
 			if (status)
 				goto out;
 			break;
@@ -950,7 +948,7 @@ nfsd4_decode_open(struct nfsd4_compoundargs *argp, struct nfsd4_open *open)
 			COPYMEM(open->op_verf.data, NFS4_VERIFIER_SIZE);
 			status = nfsd4_decode_fattr(argp, open->op_bmval,
 				&open->op_iattr, &open->op_acl, &open->op_label,
-				&current->fs->umask);
+				&open->op_umask);
 			if (status)
 				goto out;
 			break;
diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
index 468020fe2a07..17c453a7999c 100644
--- a/fs/nfsd/xdr4.h
+++ b/fs/nfsd/xdr4.h
@@ -119,6 +119,7 @@ struct nfsd4_create {
 	} u;
 	u32		cr_bmval[3];        /* request */
 	struct iattr	cr_iattr;           /* request */
+	int		cr_umask;           /* request */
 	struct nfsd4_change_info  cr_cinfo; /* response */
 	struct nfs4_acl *cr_acl;
 	struct xdr_netobj cr_label;
@@ -230,6 +231,7 @@ struct nfsd4_open {
 	u32		op_why_no_deleg;    /* response - DELEG_NONE_EXT only */
 	u32		op_create;     	    /* request */
 	u32		op_createmode;      /* request */
+	int		op_umask;           /* request */
 	u32		op_bmval[3];        /* request */
 	struct iattr	op_iattr;           /* UNCHECKED4, GUARDED4, EXCLUSIVE4_1 */
 	nfs4_verifier	op_verf __attribute__((aligned(32)));