btrfs: tree-checker: Verify dev item

[BUG]
For fuzzed image whose DEV_ITEM has invalid total_bytes as 0, then
kernel will just panic:
  BUG: unable to handle kernel NULL pointer dereference at 0000000000000098
  #PF error: [normal kernel read fault]
  PGD 800000022b2bd067 P4D 800000022b2bd067 PUD 22b2bc067 PMD 0
  Oops: 0000 [#1] SMP PTI
  CPU: 0 PID: 1106 Comm: mount Not tainted 5.0.0-rc8+ #9
  RIP: 0010:btrfs_verify_dev_extents+0x2a5/0x5a0
  Call Trace:
   open_ctree+0x160d/0x2149
   btrfs_mount_root+0x5b2/0x680

[CAUSE]
If device extent verification finds a deivce with 0 total_bytes, then it
assumes it's a seed dummy, then search for seed devices.

But in this case, there is no seed device at all, causing NULL pointer.

[FIX]
Since this is caused by fuzzed image, let's go the tree-check way, just
add a new verification for device item.

Reported-by: Yoon Jungyeon <jungyeon@gatech.edu>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=202691
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: David Sterba <dsterba@suse.com>

3 files changed, 83 insertions, 9 deletions

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index 33d04fc4d280..00ab4e783b9f 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -600,6 +600,77 @@ int btrfs_check_chunk_valid(struct btrfs_fs_info *fs_info,
         return 0;
 }
 
+__printf(4, 5)
+__cold
+static void dev_item_err(const struct btrfs_fs_info *fs_info,
+                         const struct extent_buffer *eb, int slot,
+                         const char *fmt, ...)
+{
+        struct btrfs_key key;
+        struct va_format vaf;
+        va_list args;
+
+        btrfs_item_key_to_cpu(eb, &key, slot);
+        va_start(args, fmt);
+
+        vaf.fmt = fmt;
+        vaf.va = &args;
+
+        btrfs_crit(fs_info,
+        "corrupt %s: root=%llu block=%llu slot=%d devid=%llu %pV",
+                btrfs_header_level(eb) == 0 ? "leaf" : "node",
+                btrfs_header_owner(eb), btrfs_header_bytenr(eb), slot,
+                key.objectid, &vaf);
+        va_end(args);
+}
+
+static int check_dev_item(struct btrfs_fs_info *fs_info,
+                          struct extent_buffer *leaf,
+                          struct btrfs_key *key, int slot)
+{
+        struct btrfs_dev_item *ditem;
+        u64 max_devid = max(BTRFS_MAX_DEVS(fs_info), BTRFS_MAX_DEVS_SYS_CHUNK);
+
+        if (key->objectid != BTRFS_DEV_ITEMS_OBJECTID) {
+                dev_item_err(fs_info, leaf, slot,
+                             "invalid objectid: has=%llu expect=%llu",
+                             key->objectid, BTRFS_DEV_ITEMS_OBJECTID);
+                return -EUCLEAN;
+        }
+        if (key->offset > max_devid) {
+                dev_item_err(fs_info, leaf, slot,
+                             "invalid devid: has=%llu expect=[0, %llu]",
+                             key->offset, max_devid);
+                return -EUCLEAN;
+        }
+        ditem = btrfs_item_ptr(leaf, slot, struct btrfs_dev_item);
+        if (btrfs_device_id(leaf, ditem) != key->offset) {
+                dev_item_err(fs_info, leaf, slot,
+                             "devid mismatch: key has=%llu item has=%llu",
+                             key->offset, btrfs_device_id(leaf, ditem));
+                return -EUCLEAN;
+        }
+
+        /*
+         * For device total_bytes, we don't have reliable way to check it, as
+         * it can be 0 for device removal. Device size check can only be done
+         * by dev extents check.
+         */
+        if (btrfs_device_bytes_used(leaf, ditem) >
+            btrfs_device_total_bytes(leaf, ditem)) {
+                dev_item_err(fs_info, leaf, slot,
+                             "invalid bytes used: have %llu expect [0, %llu]",
+                             btrfs_device_bytes_used(leaf, ditem),
+                             btrfs_device_total_bytes(leaf, ditem));
+                return -EUCLEAN;
+        }
+        /*
+         * Remaining members like io_align/type/gen/dev_group aren't really
+         * utilized.  Skip them to make later usage of them easier.
+         */
+        return 0;
+}
+
 /*
  * Common point to switch the item-specific validation.
  */
@@ -630,6 +701,9 @@ static int check_leaf_item(struct btrfs_fs_info *fs_info,
                 ret = btrfs_check_chunk_valid(fs_info, leaf, chunk,
                                               key->offset);
                 break;
+        case BTRFS_DEV_ITEM_KEY:
+                ret = check_dev_item(fs_info, leaf, key, slot);
+                break;
         }
         return ret;
 }
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 97dbd7f37674..77bca3a61e26 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4958,15 +4958,6 @@ static void check_raid56_incompat_flag(struct btrfs_fs_info *info, u64 type)
         btrfs_set_fs_incompat(info, RAID56);
 }
 
-#define BTRFS_MAX_DEVS(info) ((BTRFS_MAX_ITEM_SIZE(info)        \
-                        - sizeof(struct btrfs_chunk))           \
-                        / sizeof(struct btrfs_stripe) + 1)
-
-#define BTRFS_MAX_DEVS_SYS_CHUNK ((BTRFS_SYSTEM_CHUNK_ARRAY_SIZE        \
-                                - 2 * sizeof(struct btrfs_disk_key)     \
-                                - 2 * sizeof(struct btrfs_chunk))       \
-                                / sizeof(struct btrfs_stripe) + 1)
-
 static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
                                u64 start, u64 type)
 {
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 3ad9d58d1b66..38ed94b77202 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -258,6 +258,15 @@ struct btrfs_fs_devices {
 
 #define BTRFS_BIO_INLINE_CSUM_SIZE      64
 
+#define BTRFS_MAX_DEVS(info) ((BTRFS_MAX_ITEM_SIZE(info)        \
+                        - sizeof(struct btrfs_chunk))           \
+                        / sizeof(struct btrfs_stripe) + 1)
+
+#define BTRFS_MAX_DEVS_SYS_CHUNK ((BTRFS_SYSTEM_CHUNK_ARRAY_SIZE        \
+                                - 2 * sizeof(struct btrfs_disk_key)     \
+                                - 2 * sizeof(struct btrfs_chunk))       \
+                                / sizeof(struct btrfs_stripe) + 1)
+
 /*
  * we need the mirror number and stripe index to be passed around
  * the call chain while we are processing end_io (especially errors).