ext4: fix type-widening bug in inode table readahead code

Due to a missing cast, the high 32-bits of a 64-bit block number used
when calculating the readahead block for inode tables can get lost.
This means we can end up fetching the wrong blocks for readahead for
file systems > 16TB.

Linus found this when experimenting with an enhacement to the sparse
static code checker which checks for missing widening casts before
binary "not" operators.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index d7518e2728f1..793d44b84d7f 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4011,13 +4011,14 @@ make_io:
                 if (EXT4_SB(sb)->s_inode_readahead_blks) {
                         ext4_fsblk_t b, end, table;
                         unsigned num;
+                        __u32 ra_blks = EXT4_SB(sb)->s_inode_readahead_blks;
 
                         table = ext4_inode_table(sb, gdp);
                         /* s_inode_readahead_blks is always a power of 2 */
-                        b = block & ~(EXT4_SB(sb)->s_inode_readahead_blks-1);
+                        b = block & ~((ext4_fsblk_t) ra_blks - 1);
                         if (table > b)
                                 b = table;
-                        end = b + EXT4_SB(sb)->s_inode_readahead_blks;
+                        end = b + ra_blks;
                         num = EXT4_INODES_PER_GROUP(sb);
                         if (ext4_has_group_desc_csum(sb))
                                 num -= ext4_itable_unused_count(sb, gdp);