ext4: fix overflow in ext4_iomap_alloc()

A code in iomap alloc may overflow block number when converting it to
byte offset. Luckily this is mostly harmless as we will just use more
expensive method of writing using unwritten extents even though we are
writing beyond i_size.

Cc: stable@kernel.org
Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210412102333.2676-4-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
(cherry picked from commit d0b040f5f2557b2f507c01e88ad8cff424fdc6a9)
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index fe6045a465993bbf4234580d34080583f3e93e35..211acfba3af7cfbca1565e7c38f0c80703c5ce86 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3418,7 +3418,7 @@ retry:
         * i_disksize out to i_size. This could be beyond where direct I/O is
         * happening and thus expose allocated blocks to direct I/O reads.
         */
-       else if ((map->m_lblk * (1 << blkbits)) >= i_size_read(inode))
+       else if (((loff_t)map->m_lblk << blkbits) >= i_size_read(inode))
                m_flags = EXT4_GET_BLOCKS_CREATE;
        else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
                m_flags = EXT4_GET_BLOCKS_IO_CREATE_EXT;