ext4: fix overflow in ext4_iomap_alloc()

commit d0b040f5f2557b2f507c01e88ad8cff424fdc6a9 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3f11c948feb026c056c0f495e191cfa125bbe172..18a5321b5ef37d6500cb3fd9464fd3e68c13a140 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3419,7 +3419,7 @@ 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;