> On Jun 25, 2021, at 2:57 PM, Trond Myklebust <trondmy@xxxxxxxxxxxxxxx> wrote:
>
> On Fri, 2021-06-25 at 18:05 +0000, Chuck Lever III wrote:
>>
>>
>>> On Jun 25, 2021, at 12:28 PM, Trond Myklebust
>>> <trondmy@xxxxxxxxxxxxxxx> wrote:
>>>
>>> On Fri, 2021-06-25 at 11:12 -0400, Chuck Lever wrote:
>>>> The double copy of the string is a mistake, plus __assign_str()
>>>> uses strlen(), which is wrong to do on a string that isn't
>>>> guaranteed to be NUL-terminated.
>>>>
>>>> Fixes: 6019ce0742ca ("NFSD: Add a tracepoint to record directory
>>>> entry encoding")
>>>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>>> ---
>>>> fs/nfsd/trace.h | 1 -
>>>> 1 file changed, 1 deletion(-)
>>>>
>>>> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
>>>> index 27a93ebd1d80..89dccced526a 100644
>>>> --- a/fs/nfsd/trace.h
>>>> +++ b/fs/nfsd/trace.h
>>>> @@ -408,7 +408,6 @@ TRACE_EVENT(nfsd_dirent,
>>>> __entry->ino = ino;
>>>> __entry->len = namlen;
>>>> memcpy(__get_str(name), name, namlen);
>>>> - __assign_str(name, name);
>>>> ),
>>>> TP_printk("fh_hash=0x%08x ino=%llu name=%.*s",
>>>> __entry->fh_hash, __entry->ino,
>>>>
>>>>
>>>
>>> Why not just store it as a NUL terminated string and save a few bytes
>>> by getting rid of the integer-sized storage of the length?
>>
>> Stephen is adding some helpers to do that in the next merge
>> window. For now, I need to fix this oops, and this is the
>> fastest way to do that.
>
>
> Won't this suffice?
Yes of course it will. As I said, Stephen has some trace
macros lines up for the next merge window that I would
prefer to use. I will be posting patches that use those
as soon as 5.14-rc1 appears.
For now, a single line fix is needed to prevent an oops
in 5.13.
> 8<---------------------------------------
> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> index 27a93ebd1d80..799168774ccf 100644
> --- a/fs/nfsd/trace.h
> +++ b/fs/nfsd/trace.h
> @@ -400,19 +400,17 @@ TRACE_EVENT(nfsd_dirent,
> TP_STRUCT__entry(
> __field(u32, fh_hash)
> __field(u64, ino)
> - __field(int, len)
> - __dynamic_array(unsigned char, name, namlen)
> + __dynamic_array(unsigned char, name, namlen + 1)
> ),
> TP_fast_assign(
> __entry->fh_hash = fhp ? knfsd_fh_hash(&fhp->fh_handle) : 0;
> __entry->ino = ino;
> - __entry->len = namlen;
> memcpy(__get_str(name), name, namlen);
> - __assign_str(name, name);
> + __get_str(name)[namlen] = 0;
> ),
> - TP_printk("fh_hash=0x%08x ino=%llu name=%.*s",
> + TP_printk("fh_hash=0x%08x ino=%llu name=%s",
> __entry->fh_hash, __entry->ino,
> - __entry->len, __get_str(name))
> + __get_str(name))
> )
>
> #include "state.h"
>
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@xxxxxxxxxxxxxxx
--
Chuck Lever
