NFSD: Change the way the expected length of a fattr4 is checked

Because the fattr4 is now managed in an xdr_stream, all that is
needed is to store the initial position of the stream before
decoding the attribute list. Then the actual length of the list
is computed using the final stream position, after decoding is
complete.

No behavior change is expected.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4xdr.c

@@ -250,7 +250,8 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 		   struct iattr *iattr, struct nfs4_acl **acl,
 		   struct xdr_netobj *label, int *umask)
 {
-	int expected_len, len = 0;
+	unsigned int starting_pos;
+	u32 attrlist4_count;
 	u32 dummy32;
 	char *buf;
 
@@ -267,12 +268,12 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 		return nfserr_attrnotsupp;
 	}
 
-	READ_BUF(4);
-	expected_len = be32_to_cpup(p++);
+	if (xdr_stream_decode_u32(argp->xdr, &attrlist4_count) < 0)
+		return nfserr_bad_xdr;
+	starting_pos = xdr_stream_pos(argp->xdr);
 
 	if (bmval[0] & FATTR4_WORD0_SIZE) {
 		READ_BUF(8);
-		len += 8;
 		p = xdr_decode_hyper(p, &iattr->ia_size);
 		iattr->ia_valid |= ATTR_SIZE;
 	}
@@ -280,7 +281,7 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 		u32 nace;
 		struct nfs4_ace *ace;
 
-		READ_BUF(4); len += 4;
+		READ_BUF(4);
 		nace = be32_to_cpup(p++);
 
 		if (nace > xdr_stream_remaining(argp->xdr) / sizeof(struct nfs4_ace))
@@ -297,13 +298,12 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 
 		(*acl)->naces = nace;
 		for (ace = (*acl)->aces; ace < (*acl)->aces + nace; ace++) {
-			READ_BUF(16); len += 16;
+			READ_BUF(16);
 			ace->type = be32_to_cpup(p++);
 			ace->flag = be32_to_cpup(p++);
 			ace->access_mask = be32_to_cpup(p++);
 			dummy32 = be32_to_cpup(p++);
 			READ_BUF(dummy32);
-			len += XDR_QUADLEN(dummy32) << 2;
 			READMEM(buf, dummy32);
 			ace->whotype = nfs4_acl_get_whotype(buf, dummy32);
 			status = nfs_ok;
@@ -322,17 +322,14 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 		*acl = NULL;
 	if (bmval[1] & FATTR4_WORD1_MODE) {
 		READ_BUF(4);
-		len += 4;
 		iattr->ia_mode = be32_to_cpup(p++);
 		iattr->ia_mode &= (S_IFMT | S_IALLUGO);
 		iattr->ia_valid |= ATTR_MODE;
 	}
 	if (bmval[1] & FATTR4_WORD1_OWNER) {
 		READ_BUF(4);
-		len += 4;
 		dummy32 = be32_to_cpup(p++);
 		READ_BUF(dummy32);
-		len += (XDR_QUADLEN(dummy32) << 2);
 		READMEM(buf, dummy32);
 		if ((status = nfsd_map_name_to_uid(argp->rqstp, buf, dummy32, &iattr->ia_uid)))
 			return status;
@@ -340,10 +337,8 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 	}
 	if (bmval[1] & FATTR4_WORD1_OWNER_GROUP) {
 		READ_BUF(4);
-		len += 4;
 		dummy32 = be32_to_cpup(p++);
 		READ_BUF(dummy32);
-		len += (XDR_QUADLEN(dummy32) << 2);
 		READMEM(buf, dummy32);
 		if ((status = nfsd_map_name_to_gid(argp->rqstp, buf, dummy32, &iattr->ia_gid)))
 			return status;
@@ -351,11 +346,9 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 	}
 	if (bmval[1] & FATTR4_WORD1_TIME_ACCESS_SET) {
 		READ_BUF(4);
-		len += 4;
 		dummy32 = be32_to_cpup(p++);
 		switch (dummy32) {
 		case NFS4_SET_TO_CLIENT_TIME:
-			len += 12;
 			status = nfsd4_decode_time(argp, &iattr->ia_atime);
 			if (status)
 				return status;
@@ -370,11 +363,9 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 	}
 	if (bmval[1] & FATTR4_WORD1_TIME_MODIFY_SET) {
 		READ_BUF(4);
-		len += 4;
 		dummy32 = be32_to_cpup(p++);
 		switch (dummy32) {
 		case NFS4_SET_TO_CLIENT_TIME:
-			len += 12;
 			status = nfsd4_decode_time(argp, &iattr->ia_mtime);
 			if (status)
 				return status;
@@ -392,18 +383,14 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 	if (IS_ENABLED(CONFIG_NFSD_V4_SECURITY_LABEL) &&
 	    bmval[2] & FATTR4_WORD2_SECURITY_LABEL) {
 		READ_BUF(4);
-		len += 4;
 		dummy32 = be32_to_cpup(p++); /* lfs: we don't use it */
 		READ_BUF(4);
-		len += 4;
 		dummy32 = be32_to_cpup(p++); /* pi: we don't use it either */
 		READ_BUF(4);
-		len += 4;
 		dummy32 = be32_to_cpup(p++);
 		READ_BUF(dummy32);
 		if (dummy32 > NFS4_MAXLABELLEN)
 			return nfserr_badlabel;
-		len += (XDR_QUADLEN(dummy32) << 2);
 		READMEM(buf, dummy32);
 		label->len = dummy32;
 		label->data = svcxdr_dupstr(argp, buf, dummy32);
@@ -414,15 +401,16 @@ nfsd4_decode_fattr(struct nfsd4_compoundargs *argp, u32 *bmval,
 		if (!umask)
 			goto xdr_error;
 		READ_BUF(8);
-		len += 8;
 		dummy32 = be32_to_cpup(p++);
 		iattr->ia_mode = dummy32 & (S_IFMT | S_IALLUGO);
 		dummy32 = be32_to_cpup(p++);
 		*umask = dummy32 & S_IRWXUGO;
 		iattr->ia_valid |= ATTR_MODE;
 	}
-	if (len != expected_len)
-		goto xdr_error;
+
+	/* request sanity: did attrlist4 contain the expected number of words? */
+	if (attrlist4_count != xdr_stream_pos(argp->xdr) - starting_pos)
+		return nfserr_bad_xdr;
 
 	DECODE_TAIL;
 }