2 files changed, 27 insertions, 4 deletions

diff --git a/drivers/mtd/ubi/attach.c b/drivers/mtd/ubi/attach.c
index bd6fc528b10a..903becd31410 100644
--- a/drivers/mtd/ubi/attach.c
+++ b/drivers/mtd/ubi/attach.c
@@ -856,13 +856,15 @@ static bool vol_ignored(int vol_id)
  * @ubi: UBI device description object
  * @ai: attaching information
  * @pnum: the physical eraseblock number
+ * @fast: true if we're scanning for a Fastmap
  *
  * This function reads UBI headers of PEB @pnum, checks them, and adds
  * information about this PEB to the corresponding list or RB-tree in the
  * "attaching info" structure. Returns zero if the physical eraseblock was
  * successfully handled and a negative error code in case of failure.
  */
-static int scan_peb(struct ubi_device *ubi, struct ubi_attach_info *ai, int pnum)
+static int scan_peb(struct ubi_device *ubi, struct ubi_attach_info *ai,
+                    int pnum, bool fast)
 {
         long long ec;
         int err, bitflips = 0, vol_id = -1, ec_err = 0;
@@ -980,6 +982,20 @@ static int scan_peb(struct ubi_device *ubi, struct ubi_attach_info *ai, int pnum
                          */
                         ai->maybe_bad_peb_count += 1;
         case UBI_IO_BAD_HDR:
+                        /*
+                         * If we're facing a bad VID header we have to drop *all*
+                         * Fastmap data structures we find. The most recent Fastmap
+                         * could be bad and therefore there is a chance that we attach
+                         * from an old one. On a fine MTD stack a PEB must not render
+                         * bad all of a sudden, but the reality is different.
+                         * So, let's be paranoid and help finding the root cause by
+                         * falling back to scanning mode instead of attaching with a
+                         * bad EBA table and cause data corruption which is hard to
+                         * analyze.
+                         */
+                        if (fast)
+                                ai->force_full_scan = 1;
+
                 if (ec_err)
                         /*
                          * Both headers are corrupted. There is a possibility
@@ -1293,7 +1309,7 @@ static int scan_all(struct ubi_device *ubi, struct ubi_attach_info *ai,
                 cond_resched();
 
                 dbg_gen("process PEB %d", pnum);
-                err = scan_peb(ubi, ai, pnum);
+                err = scan_peb(ubi, ai, pnum, false);
                 if (err < 0)
                         goto out_vidh;
         }
@@ -1407,7 +1423,7 @@ static int scan_fast(struct ubi_device *ubi, struct ubi_attach_info **ai)
                 cond_resched();
 
                 dbg_gen("process PEB %d", pnum);
-                err = scan_peb(ubi, scan_ai, pnum);
+                err = scan_peb(ubi, scan_ai, pnum, true);
                 if (err < 0)
                         goto out_vidh;
         }
@@ -1415,7 +1431,11 @@ static int scan_fast(struct ubi_device *ubi, struct ubi_attach_info **ai)
         ubi_free_vid_hdr(ubi, vidh);
         kfree(ech);
 
-        err = ubi_scan_fastmap(ubi, *ai, scan_ai);
+        if (scan_ai->force_full_scan)
+                err = UBI_NO_FASTMAP;
+        else
+                err = ubi_scan_fastmap(ubi, *ai, scan_ai);
+
         if (err) {
                 /*
                  * Didn't attach via fastmap, do a full scan but reuse what
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index c8b90a866d27..b616a115c9d3 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -715,6 +715,8 @@ struct ubi_ainf_volume {
  * @vols_found: number of volumes found
  * @highest_vol_id: highest volume ID
  * @is_empty: flag indicating whether the MTD device is empty or not
+ * @force_full_scan: flag indicating whether we need to do a full scan and drop
+                     all existing Fastmap data structures
  * @min_ec: lowest erase counter value
  * @max_ec: highest erase counter value
  * @max_sqnum: highest sequence number value
@@ -742,6 +744,7 @@ struct ubi_attach_info {
         int vols_found;
         int highest_vol_id;
         int is_empty;
+        int force_full_scan;
         int min_ec;
         int max_ec;
         unsigned long long max_sqnum;