[PATCH v2 2/2] nfsd: Eliminate an allocation in nfs4_make_rec_clidname()

[Eric Biggers <ebiggers@xxxxxxxxxx>]

Since MD5 digests are fixed-size, make nfs4_make_rec_clidname() store
the digest in a stack buffer instead of a dynamically allocated buffer.
Use MD5_DIGEST_SIZE instead of a hard-coded value, both in
nfs4_make_rec_clidname() and in the definition of HEXDIR_LEN.

Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
 fs/nfsd/nfs4recover.c | 15 ++++-----------
 fs/nfsd/state.h       |  4 +++-
 2 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 54f5e5392ef9..e2b9472e5c78 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -93,11 +93,11 @@ nfs4_reset_creds(const struct cred *original)
 }
 
 static int
 nfs4_make_rec_clidname(char dname[HEXDIR_LEN], const struct xdr_netobj *clname)
 {
-	struct xdr_netobj cksum;
+	u8 digest[MD5_DIGEST_SIZE];
 	struct crypto_shash *tfm;
 	int status;
 
 	dprintk("NFSD: nfs4_make_rec_clidname for %.*s\n",
 			clname->len, clname->data);
@@ -105,27 +105,20 @@ nfs4_make_rec_clidname(char dname[HEXDIR_LEN], const struct xdr_netobj *clname)
 	if (IS_ERR(tfm)) {
 		status = PTR_ERR(tfm);
 		goto out_no_tfm;
 	}
 
-	cksum.len = crypto_shash_digestsize(tfm);
-	cksum.data = kmalloc(cksum.len, GFP_KERNEL);
-	if (cksum.data == NULL) {
-		status = -ENOMEM;
- 		goto out;
-	}
-
 	status = crypto_shash_tfm_digest(tfm, clname->data, clname->len,
-					 cksum.data);
+					 digest);
 	if (status)
 		goto out;
 
-	sprintf(dname, "%*phN", 16, cksum.data);
+	static_assert(HEXDIR_LEN == 2 * MD5_DIGEST_SIZE + 1);
+	sprintf(dname, "%*phN", MD5_DIGEST_SIZE, digest);
 
 	status = 0;
 out:
-	kfree(cksum.data);
 	crypto_free_shash(tfm);
 out_no_tfm:
 	return status;
 }
 
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index 8adc2550129e..b7d4c6d6f3d4 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -33,10 +33,11 @@
  */
 
 #ifndef _NFSD4_STATE_H
 #define _NFSD4_STATE_H
 
+#include <crypto/md5.h>
 #include <linux/idr.h>
 #include <linux/refcount.h>
 #include <linux/sunrpc/svc_xprt.h>
 #include "nfsfh.h"
 #include "nfsd.h"
@@ -379,11 +380,12 @@ struct nfsd4_sessionid {
 	clientid_t	clientid;
 	u32		sequence;
 	u32		reserved;
 };
 
-#define HEXDIR_LEN     33 /* hex version of 16 byte md5 of cl_name plus '\0' */
+/* Length of MD5 digest as hex, plus terminating '\0' */
+#define HEXDIR_LEN	(2 * MD5_DIGEST_SIZE + 1)
 
 /*
  *       State                Meaning                  Where set
  * --------------------------------------------------------------------------
  * | NFSD4_ACTIVE      | Confirmed, active    | Default                     |
-- 
2.50.1.565.gc32cd1483b-goog