ext4: fix trimming starting with block 0 with small blocksize

When s_first_data_block is not zero (which happens e.g. when block size is 1KB)
and trim ioctl is called to start trimming from block 0, the math in
ext4_get_group_no_and_offset() overflows. The overall result is that ioctl
returns EINVAL which is kind of unexpected and we probably don't want
userspace tools to bother with internal details of filesystem structure.
So just silently increase starting offset (and shorten length) when starting
block is below s_first_data_block.

CC: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index cc1297e15f1b49023fed36d92215e535444e3658..851f49b2f9d24e6715dae75459b344019c7351fe 100644 (file)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4808,6 +4808,8 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
        ext4_group_t group, ngroups = ext4_get_groups_count(sb);
        ext4_grpblk_t cnt = 0, first_block, last_block;
        uint64_t start, len, minlen, trimmed;
+       ext4_fsblk_t first_data_blk =
+                       le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block);
        int ret = 0;
 
        start = range->start >> sb->s_blocksize_bits;
@@ -4817,6 +4819,10 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range)
 
        if (unlikely(minlen > EXT4_BLOCKS_PER_GROUP(sb)))
                return -EINVAL;
+       if (start < first_data_blk) {
+               len -= first_data_blk - start;
+               start = first_data_blk;
+       }
 
        /* Determine first and last group to examine based on start and len */
        ext4_get_group_no_and_offset(sb, (ext4_fsblk_t) start,