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SubjectRe: [PATCH -next 1/1] iomap: Fix a false positive of UBSAN in iomap_seek_data()
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On 2021/7/2 19:50, Leizhen (ThunderTown) wrote:
>
>
> On 2021/7/2 17:34, Christoph Hellwig wrote:
>> We might as well just kill off the length variable while we're at it:
>
> Hi, Christoph:
> Maybe you need to write a separate patch. Because the patch I sent is
> to modify function iomap_seek_data(). I didn't look at the other functions.
> In fact, both iomap_seek_data() and iomap_seek_hole() need to be modified.
> The iomap_seek_data() may not be intuitive to delete the variable 'length'.
>
> I'm now analyzing if the "if (length <= 0)" statement in iomap_seek_data()
> is redundant (the condition is never true).

I've thought about it, and that "if" statement can be removed as follows:

diff --git a/fs/iomap/seek.c b/fs/iomap/seek.c
index dab1b02eba5b..dc55f9ecd948 100644
--- a/fs/iomap/seek.c
+++ b/fs/iomap/seek.c
@@ -96,14 +96,13 @@ iomap_seek_data(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
if (ret < 0)
return ret;
if (ret == 0)
- break;
+ return offset;

offset += ret;
length -= ret;
}

- if (length <= 0)
- return -ENXIO;
- return offset;
+ /* The end of the file is reached, and no data is found */
+ return -ENXIO;
}
EXPORT_SYMBOL_GPL(iomap_seek_data);


>
>>
>>
>> diff --git a/fs/iomap/seek.c b/fs/iomap/seek.c
>> index dab1b02eba5b7f..942e354e9e13e6 100644
>> --- a/fs/iomap/seek.c
>> +++ b/fs/iomap/seek.c
>> @@ -35,23 +35,21 @@ loff_t
>> iomap_seek_hole(struct inode *inode, loff_t offset, const struct iomap_ops *ops)
>> {
>> loff_t size = i_size_read(inode);
>> - loff_t length = size - offset;
>> loff_t ret;
>>
>> /* Nothing to be found before or beyond the end of the file. */
>> if (offset < 0 || offset >= size)
>> return -ENXIO;
>>
>> - while (length > 0) {
>> - ret = iomap_apply(inode, offset, length, IOMAP_REPORT, ops,
>> - &offset, iomap_seek_hole_actor);
>> + while (offset < size) {
>> + ret = iomap_apply(inode, offset, size - offset, IOMAP_REPORT,
>> + ops, &offset, iomap_seek_hole_actor);
>> if (ret < 0)
>> return ret;
>> if (ret == 0)
>> break;
>>
>> offset += ret;
>> - length -= ret;
>> }
>>
>> return offset;
>>
>> .
>>

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