kernel: don't auto attach ubi on read error

With a10a204aab ("kernel: make ubi auto-attach check for a tar file
magic") the check for the magic was added without considering a failing
mtd_read(). If the read fails, no check is done and the mount code is
called straight away.

Failing with an error message for such cases seems to me the cleaner way,
as it would allow to spot hidden/workaround issues.

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/generic/pending-4.14/490-ubi-auto-attach-mtd-device-named-ubi-or-data-on-boot.patch

@@ -8,7 +8,7 @@ Signed-off-by: Daniel Golle <daniel@makrotopia.org>
 
 --- a/drivers/mtd/ubi/build.c
 +++ b/drivers/mtd/ubi/build.c
-@@ -1171,6 +1171,68 @@ static struct mtd_info * __init open_mtd
+@@ -1171,6 +1171,73 @@ static struct mtd_info * __init open_mtd
  	return mtd;
  }
  
@@ -44,10 +44,15 @@ Signed-off-by: Daniel Golle <daniel@makrotopia.org>
 +			}
 +		}
 +
-+	/* check for a valid ubi magic if read from flash was successful */
++	/* check if the read from flash was successful */
 +	err = mtd_read(mtd, offset, 4, &len, (void *) magic);
-+	if ((!err || mtd_is_bitflip(err)) &&
-+	    len == 4 && strncmp(magic, "UBI#", 4)) {
++	if ((err && !mtd_is_bitflip(err)) || len != 4) {
++		pr_err("UBI error: unable to read from mtd%d\n", mtd->index);
++		goto cleanup;
++	}
++
++	/* check for a valid ubi magic */
++	if (strncmp(magic, "UBI#", 4)) {
 +		pr_err("UBI error: no valid UBI magic found inside mtd%d\n", mtd->index);
 +		goto cleanup;
 +	}
@@ -77,7 +82,7 @@ Signed-off-by: Daniel Golle <daniel@makrotopia.org>
  static int __init ubi_init(void)
  {
  	int err, i, k;
-@@ -1254,6 +1316,12 @@ static int __init ubi_init(void)
+@@ -1254,6 +1321,12 @@ static int __init ubi_init(void)
  		}
  	}
  

target/linux/generic/pending-4.9/490-ubi-auto-attach-mtd-device-named-ubi-or-data-on-boot.patch

@@ -8,7 +8,7 @@ Signed-off-by: Daniel Golle <daniel@makrotopia.org>
 
 --- a/drivers/mtd/ubi/build.c
 +++ b/drivers/mtd/ubi/build.c
-@@ -1226,6 +1226,68 @@ static struct mtd_info * __init open_mtd
+@@ -1226,6 +1226,73 @@ static struct mtd_info * __init open_mtd
  	return mtd;
  }
  
@@ -44,10 +44,15 @@ Signed-off-by: Daniel Golle <daniel@makrotopia.org>
 +			}
 +		}
 +
-+	/* check for a valid ubi magic if read from flash was successful */
++	/* check if the read from flash was successful */
 +	err = mtd_read(mtd, offset, 4, &len, (void *) magic);
-+	if ((!err || mtd_is_bitflip(err)) &&
-+	    len == 4 && strncmp(magic, "UBI#", 4)) {
++	if ((err && !mtd_is_bitflip(err)) || len != 4) {
++		pr_err("UBI error: unable to read from mtd%d\n", mtd->index);
++		goto cleanup;
++	}
++
++	/* check for a valid ubi magic */
++	if (strncmp(magic, "UBI#", 4)) {
 +		pr_err("UBI error: no valid UBI magic found inside mtd%d\n", mtd->index);
 +		goto cleanup;
 +	}
@@ -77,7 +82,7 @@ Signed-off-by: Daniel Golle <daniel@makrotopia.org>
  static int __init ubi_init(void)
  {
  	int err, i, k;
-@@ -1309,6 +1371,12 @@ static int __init ubi_init(void)
+@@ -1309,6 +1376,12 @@ static int __init ubi_init(void)
  		}
  	}