Re: [PATCH] fs/ntfs3: reject evcn == U64_MAX in mi_enum_attr()

[David Laight]

On Fri, 24 Apr 2026 21:20:31 +0800
Zhan Xusheng <zhanxusheng1024@xxxxxxxxx> wrote:

> Hi David,
> 
> That would reject the svcn == evcn case, which represents a
> single-cluster extent (e.g. svcn=0, evcn=0) and is currently
> treated as valid.

Slight brain fade..

> 
> The original check allows svcn == evcn + 1 (empty range), so the
> condition is strictly "greater than", not "greater than or equal".
> 
> The issue here is the overflow of (evcn + 1) when evcn == U64_MAX,
> which turns the check into "svcn > 0" and incorrectly allows
> svcn == 0.

Is that analysis correct? with the current code:
If evcn is 2 then everything except 0, 1, 2 and 3 are errors.
If evcn is -3 then only -1 is an error.
If evcn is -2 no values are errors.
If evcn is -1 then all svcn values except 0 are errors.

Clearly this doesn't make sense if evcn is -1.

But there isn't an obvious reason why svcn == -4, evcn == -1
shouldn't be a valid range.
(There might be a sanity upper limit is evcn for other reasons.)

	David
 
> 
> My patch preserves the existing semantics and only adds the
> missing U64_MAX guard.
> 
> Thanks,
> Zhan Xusheng
>