Leonard Michlmayr wrote:
> Akira Fujita:
>> <kernel-space>
>> fs/ioctl.c ioctl_fimap():
>>
>> filemap_check_ranges():
>> len(~0ULL)
>> new_len(4398046511103 = s_maxbytes) <--- Because 'len > s_maxbytes'
>>
>> fs/ext4/extents.c ext4_fiemap():
>> last_blk = start(0) + len(4398046511103) - 1 >> s_blocksize_bits(11)
>> = 4294967295 (0xFFFFFFFF)
>> len_blks = 4294967295 + 1 (0xFFFFFFFF + 0x00000001)
>> = 4294967296 (0x100000000) <--- _OVERFLOW!!_
>>
>> ext4_ext_walk_space():
>> num = 0
>>
>> This overflow leads to incorrect output like the below,
>> even though 2 extents exist.
>>
>
> Thank you for pointing this out. I had not checked s_maxbytes.
> Appearently s_maxbytes can be 1<<(32 + s_blocksize_bits) - 1. Therefore
> the number of blocks in a file cannot be stored in a 32bit integer.
For extent-based files it had better be....
struct ext4_extent {
__le32 ee_block; /* first logical block extent covers */
__le16 ee_len; /* number of blocks covered by extent */
The start block can't be more than 32 bits; this essentially limits
the file size / maximum logical block to 2^32 blocks right?
s_maxbytes comes out to 17592186044415
2^32 4k blocks is 17592186044416 bytes, or max byte offset 17592186044415
What am I missing? (confusion between max byte count and max
byte offset, perhaps?)
-Eric
> I have a patch that should fix it for fiemap. I have just compiled it
> and I will do some testing and double checking tomorrow. I will send a
> separate email with the patch.
>
> regards
> Leonard
>
>
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