dm: refine the check of return value of snprintf

int snprintf(char *str, size_t size, const char *format, ...)
The functions snprintf() write at most size bytes (including the
terminating null byte('\0')) to str.
only when returned value of snprintf is non-negative and less than size,
the string has been completely written.

Tracked-On: #4087
Signed-off-by: Gao Junhao <junhao.gao@intel.com>
Reviewed-by: Yonghua Huang <yonghua.huang@intel.com>
Acked-by: Yu Wang <yu1.wang@intel.com>

Author: gaojunhao0504

devicemodel/hw/pci/ahci.c

@@ -2383,8 +2383,8 @@ pci_ahci_init(struct vmctx *ctx, struct pci_vdev *dev, char *opts, int atapi)
 			sizeof(ahci_dev->port[p].ident),
 			"ACRN--%02X%02X-%02X%02X-%02X%02X", digest[0],
 			digest[1], digest[2], digest[3], digest[4], digest[5]);
-		if (rc > sizeof(ahci_dev->port[p].ident))
-			WPRINTF("%s: digest is longer than ident\n", __func__);
+		if (rc >= sizeof(ahci_dev->port[p].ident) || rc < 0)
+			WPRINTF("%s: digest number is invalid!\n", __func__);
 
 		/*
 		 * Allocate blockif request structures and add them

devicemodel/hw/pci/npk.c

@@ -243,8 +243,8 @@ static int pci_npk_init(struct vmctx *ctx, struct pci_vdev *dev, char *opts)
 	/* read the host NPK configuration space */
 	rc = snprintf(name, PATH_MAX, "%s/%s/config", NPK_DRV_SYSFS_PATH,
 			dent->d_name);
-	if (rc > PATH_MAX)
-		WPRINTF(("NPK device name too long\n"));
+	if (rc >= PATH_MAX || rc < 0)
+		WPRINTF(("NPK device name is invalid!\n"));
 
 	closedir(dir);
 	fd = open(name, O_RDONLY);

devicemodel/hw/pci/virtio/virtio_block.c

@@ -427,12 +427,12 @@ virtio_blk_init(struct vmctx *ctx, struct pci_vdev *dev, char *opts)
 	MD5_Init(&mdctx);
 	MD5_Update(&mdctx, opts, strnlen(opts, VIRTIO_BLK_MAX_OPTS_LEN));
 	MD5_Final(digest, &mdctx);
-	if (snprintf(blk->ident, sizeof(blk->ident),
+	rc = snprintf(blk->ident, sizeof(blk->ident),
 		"ACRN--%02X%02X-%02X%02X-%02X%02X", digest[0],
-		digest[1], digest[2], digest[3], digest[4],
-		digest[5]) >= sizeof(blk->ident)) {
-		WPRINTF(("virtio_blk: block ident too long\n"));
-	}
+		digest[1], digest[2], digest[3], digest[4], digest[5]);
+
+	if (rc >= sizeof(blk->ident) || rc < 0)
+		WPRINTF(("virtio_blk: block ident is invalid!\n"));
 
 	/* setup virtio block config space */
 	blk->cfg.capacity = size / DEV_BSIZE; /* 512-byte units */