ext4: check to make make sure bd_dev is set before dereferencing it

There are some drivers which may not set bdev->bd_dev.  So make sure
it is non-NULL before dereferencing it.

Google-Bug-Id: 1773557

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 13 insertions, 4 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c1036bc8a539..e046eba24782 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2304,6 +2304,8 @@ static ssize_t session_write_kbytes_show(struct ext4_attr *a,
 {
         struct super_block *sb = sbi->s_buddy_cache->i_sb;
 
+        if (!sb->s_bdev->bd_part)
+                return snprintf(buf, PAGE_SIZE, "0\n");
         return snprintf(buf, PAGE_SIZE, "%lu\n",
                         (part_stat_read(sb->s_bdev->bd_part, sectors[1]) -
                          sbi->s_sectors_written_start) >> 1);
@@ -2314,6 +2316,8 @@ static ssize_t lifetime_write_kbytes_show(struct ext4_attr *a,
 {
         struct super_block *sb = sbi->s_buddy_cache->i_sb;
 
+        if (!sb->s_bdev->bd_part)
+                return snprintf(buf, PAGE_SIZE, "0\n");
         return snprintf(buf, PAGE_SIZE, "%llu\n",
                         (unsigned long long)(sbi->s_kbytes_written +
                         ((part_stat_read(sb->s_bdev->bd_part, sectors[1]) -
@@ -2575,8 +2579,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
         sbi->s_resgid = EXT4_DEF_RESGID;
         sbi->s_inode_readahead_blks = EXT4_DEF_INODE_READAHEAD_BLKS;
         sbi->s_sb_block = sb_block;
-        sbi->s_sectors_written_start = part_stat_read(sb->s_bdev->bd_part,
-                                                      sectors[1]);
+        if (sb->s_bdev->bd_part)
+                sbi->s_sectors_written_start =
+                        part_stat_read(sb->s_bdev->bd_part, sectors[1]);
 
         unlock_kernel();
 
@@ -3492,10 +3497,14 @@ static int ext4_commit_super(struct super_block *sb, int sync)
          */
         if (!(sb->s_flags & MS_RDONLY))
                 es->s_wtime = cpu_to_le32(get_seconds());
-        es->s_kbytes_written =
-                cpu_to_le64(EXT4_SB(sb)->s_kbytes_written +
+        if (sb->s_bdev->bd_part)
+                es->s_kbytes_written =
+                        cpu_to_le64(EXT4_SB(sb)->s_kbytes_written +
                             ((part_stat_read(sb->s_bdev->bd_part, sectors[1]) -
                               EXT4_SB(sb)->s_sectors_written_start) >> 1));
+        else
+                es->s_kbytes_written =
+                        cpu_to_le64(EXT4_SB(sb)->s_kbytes_written);
         ext4_free_blocks_count_set(es, percpu_counter_sum_positive(
                                         &EXT4_SB(sb)->s_freeblocks_counter));
         es->s_free_inodes_count = cpu_to_le32(percpu_counter_sum_positive(