[PATCH] libbpf: fix str_has_sfx()

[PATCH] libbpf: fix str_has_sfx()

[Dan Carpenter]

The return from strcmp() is inverted so the it returns true instead
of false and vise versa.

Fixes: a1c9d61b19cb ("libbpf: Improve library identification for uprobe binary path resolution")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
Spotted during review.  *cmp() functions should always have a comparison
to zero.
	if (strcmp(a, b) < 0) {  <-- means a < b
	if (strcmp(a, b) >= 0) { <-- means a >= b
	if (strcmp(a, b) != 0) { <-- means a != b
etc.

 tools/lib/bpf/libbpf_internal.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 9cd7829cbe41..008485296a29 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
 	size_t str_len = strlen(str);
 	size_t sfx_len = strlen(sfx);
 
-	if (sfx_len <= str_len)
-		return strcmp(str + str_len - sfx_len, sfx);
-	return false;
+	if (sfx_len > str_len)
+		return false;
+	return strcmp(str + str_len - sfx_len, sfx) == 0;
 }
 
 /* Symbol versioning is different between static and shared library.
-- 
2.35.1

Re: [PATCH] libbpf: fix str_has_sfx()

[Martin KaFai Lau]

On Tue, Jul 19, 2022 at 12:53:01PM +0300, Dan Carpenter wrote:
> The return from strcmp() is inverted so the it returns true instead
> of false and vise versa.
> 
> Fixes: a1c9d61b19cb ("libbpf: Improve library identification for uprobe binary path resolution")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> Spotted during review.  *cmp() functions should always have a comparison
> to zero.
> 	if (strcmp(a, b) < 0) {  <-- means a < b
> 	if (strcmp(a, b) >= 0) { <-- means a >= b
> 	if (strcmp(a, b) != 0) { <-- means a != b
> etc.
> 
>  tools/lib/bpf/libbpf_internal.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> index 9cd7829cbe41..008485296a29 100644
> --- a/tools/lib/bpf/libbpf_internal.h
> +++ b/tools/lib/bpf/libbpf_internal.h
> @@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
>  	size_t str_len = strlen(str);
>  	size_t sfx_len = strlen(sfx);
>  
> -	if (sfx_len <= str_len)
> -		return strcmp(str + str_len - sfx_len, sfx);
> -	return false;
> +	if (sfx_len > str_len)
> +		return false;
> +	return strcmp(str + str_len - sfx_len, sfx) == 0;
Please tag the subject with "bpf" next time.

Acked-by: Martin KaFai Lau <kafai@fb.com>

Re: [PATCH] libbpf: fix str_has_sfx()

[Dan Carpenter]

On Tue, Jul 19, 2022 at 10:19:02AM -0700, Martin KaFai Lau wrote:
> > @@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
> >  	size_t str_len = strlen(str);
> >  	size_t sfx_len = strlen(sfx);
> >  
> > -	if (sfx_len <= str_len)
> > -		return strcmp(str + str_len - sfx_len, sfx);
> > -	return false;
> > +	if (sfx_len > str_len)
> > +		return false;
> > +	return strcmp(str + str_len - sfx_len, sfx) == 0;
> Please tag the subject with "bpf" next time.

I always work against linux-next.  Would it help if I put that in the
subject?

Otherwise I don't have a way to figure this stuff out.  I kind of know
networking tree but not 100% and that is a massive pain in the butt.
Until there is an automated way that then those kind of requests are
not reasonable.

regards,
dan carpenter

Re: [PATCH] libbpf: fix str_has_sfx()

[Alexei Starovoitov]

On Tue, Jul 19, 2022 at 10:51 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Tue, Jul 19, 2022 at 10:19:02AM -0700, Martin KaFai Lau wrote:
> > > @@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
> > >     size_t str_len = strlen(str);
> > >     size_t sfx_len = strlen(sfx);
> > >
> > > -   if (sfx_len <= str_len)
> > > -           return strcmp(str + str_len - sfx_len, sfx);
> > > -   return false;
> > > +   if (sfx_len > str_len)
> > > +           return false;
> > > +   return strcmp(str + str_len - sfx_len, sfx) == 0;
> > Please tag the subject with "bpf" next time.
>
> I always work against linux-next.  Would it help if I put that in the
> subject?
>
> Otherwise I don't have a way to figure this stuff out.  I kind of know
> networking tree but not 100% and that is a massive pain in the butt.
> Until there is an automated way that then those kind of requests are
> not reasonable.

Dan,

you were told multiple times to follow the rules.
bpf patches should target bpf of bpf-next trees only.
If you send against linux-next you're taking a random chance
that they will pass CI.
In turn making everyone waste time.
Please follow the simple rules.

Re: [PATCH] libbpf: fix str_has_sfx()

[Dan Carpenter]

On Tue, Jul 19, 2022 at 10:54:13AM -0700, Alexei Starovoitov wrote:
> On Tue, Jul 19, 2022 at 10:51 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> >
> > On Tue, Jul 19, 2022 at 10:19:02AM -0700, Martin KaFai Lau wrote:
> > > > @@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
> > > >     size_t str_len = strlen(str);
> > > >     size_t sfx_len = strlen(sfx);
> > > >
> > > > -   if (sfx_len <= str_len)
> > > > -           return strcmp(str + str_len - sfx_len, sfx);
> > > > -   return false;
> > > > +   if (sfx_len > str_len)
> > > > +           return false;
> > > > +   return strcmp(str + str_len - sfx_len, sfx) == 0;
> > > Please tag the subject with "bpf" next time.
> >
> > I always work against linux-next.  Would it help if I put that in the
> > subject?
> >
> > Otherwise I don't have a way to figure this stuff out.  I kind of know
> > networking tree but not 100% and that is a massive pain in the butt.
> > Until there is an automated way that then those kind of requests are
> > not reasonable.
> 
> Dan,
> 
> you were told multiple times to follow the rules.
> bpf patches should target bpf of bpf-next trees only.
> If you send against linux-next you're taking a random chance
> that they will pass CI.
> In turn making everyone waste time.
> Please follow the simple rules.

That's true.  We have this discussion every time and I always tell you
that the rules are untenable.  I'm just going to send bug reports to
whoever introduces bug and they can deal with it.

regards,
dan carpenter

Re: [PATCH] libbpf: fix str_has_sfx()

[Alexei Starovoitov]

On Tue, Jul 19, 2022 at 10:19 AM Martin KaFai Lau <kafai@fb.com> wrote:
>
> On Tue, Jul 19, 2022 at 12:53:01PM +0300, Dan Carpenter wrote:
> > The return from strcmp() is inverted so the it returns true instead
> > of false and vise versa.
> >
> > Fixes: a1c9d61b19cb ("libbpf: Improve library identification for uprobe binary path resolution")
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > Spotted during review.  *cmp() functions should always have a comparison
> > to zero.
> >       if (strcmp(a, b) < 0) {  <-- means a < b
> >       if (strcmp(a, b) >= 0) { <-- means a >= b
> >       if (strcmp(a, b) != 0) { <-- means a != b
> > etc.
> >
> >  tools/lib/bpf/libbpf_internal.h | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> > index 9cd7829cbe41..008485296a29 100644
> > --- a/tools/lib/bpf/libbpf_internal.h
> > +++ b/tools/lib/bpf/libbpf_internal.h
> > @@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
> >       size_t str_len = strlen(str);
> >       size_t sfx_len = strlen(sfx);
> >
> > -     if (sfx_len <= str_len)
> > -             return strcmp(str + str_len - sfx_len, sfx);
> > -     return false;
> > +     if (sfx_len > str_len)
> > +             return false;
> > +     return strcmp(str + str_len - sfx_len, sfx) == 0;
> Please tag the subject with "bpf" next time.
>
> Acked-by: Martin KaFai Lau <kafai@fb.com>

Alan,

If it was so broken how did it work earlier?
Do we have a test for this?

Re: [PATCH] libbpf: fix str_has_sfx()

[Alan Maguire]

On 19/07/2022 18:51, Alexei Starovoitov wrote:
> On Tue, Jul 19, 2022 at 10:19 AM Martin KaFai Lau <kafai@fb.com> wrote:
>>
>> On Tue, Jul 19, 2022 at 12:53:01PM +0300, Dan Carpenter wrote:
>>> The return from strcmp() is inverted so the it returns true instead
>>> of false and vise versa.
>>>
>>> Fixes: a1c9d61b19cb ("libbpf: Improve library identification for uprobe binary path resolution")
>>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
>>> ---
>>> Spotted during review.  *cmp() functions should always have a comparison
>>> to zero.
>>>       if (strcmp(a, b) < 0) {  <-- means a < b
>>>       if (strcmp(a, b) >= 0) { <-- means a >= b
>>>       if (strcmp(a, b) != 0) { <-- means a != b
>>> etc.
>>>
>>>  tools/lib/bpf/libbpf_internal.h | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
>>> index 9cd7829cbe41..008485296a29 100644
>>> --- a/tools/lib/bpf/libbpf_internal.h
>>> +++ b/tools/lib/bpf/libbpf_internal.h
>>> @@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
>>>       size_t str_len = strlen(str);
>>>       size_t sfx_len = strlen(sfx);
>>>
>>> -     if (sfx_len <= str_len)
>>> -             return strcmp(str + str_len - sfx_len, sfx);
>>> -     return false;
>>> +     if (sfx_len > str_len)
>>> +             return false;
>>> +     return strcmp(str + str_len - sfx_len, sfx) == 0;
>> Please tag the subject with "bpf" next time.
>>
>> Acked-by: Martin KaFai Lau <kafai@fb.com>
> 
> Alan,
> 
> If it was so broken how did it work earlier?
> Do we have a test for this?
> 

We have tests for automatic path determination, yes, but those
tests specify libc.so.6, so are testing the strstr(file, ".so.") 
predicate below:

	if (str_has_sfx(file, ".so") || strstr(file, ".so.")) {

Problem is, on many systems, libc.so is a GNU ld script rather
than an actual library:

cat /usr/lib64/libc.so
/* GNU ld script
   Use the shared library, but some functions are only in
   the static library, so try that secondarily.  */
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /lib64/libc.so.6 /usr/lib64/libc_nonshared.a  AS_NEEDED ( /lib64/ld-linux-x86-64.so.2 ) )

...so we can't rely on system library .so files actually containing
the library to instrument.

Maybe we can do something with liburandom_read.so now we have it
there; I was looking at extending the auto-path determination
to usdt too, so we could add a new test to cover this then I think.

Alan

Re: [PATCH] libbpf: fix str_has_sfx()

[Andrii Nakryiko]

On Wed, Jul 20, 2022 at 12:48 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> On 19/07/2022 18:51, Alexei Starovoitov wrote:
> > On Tue, Jul 19, 2022 at 10:19 AM Martin KaFai Lau <kafai@fb.com> wrote:
> >>
> >> On Tue, Jul 19, 2022 at 12:53:01PM +0300, Dan Carpenter wrote:
> >>> The return from strcmp() is inverted so the it returns true instead
> >>> of false and vise versa.
> >>>
> >>> Fixes: a1c9d61b19cb ("libbpf: Improve library identification for uprobe binary path resolution")
> >>> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> >>> ---
> >>> Spotted during review.  *cmp() functions should always have a comparison
> >>> to zero.
> >>>       if (strcmp(a, b) < 0) {  <-- means a < b
> >>>       if (strcmp(a, b) >= 0) { <-- means a >= b
> >>>       if (strcmp(a, b) != 0) { <-- means a != b
> >>> etc.
> >>>
> >>>  tools/lib/bpf/libbpf_internal.h | 6 +++---
> >>>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
> >>> index 9cd7829cbe41..008485296a29 100644
> >>> --- a/tools/lib/bpf/libbpf_internal.h
> >>> +++ b/tools/lib/bpf/libbpf_internal.h
> >>> @@ -108,9 +108,9 @@ static inline bool str_has_sfx(const char *str, const char *sfx)
> >>>       size_t str_len = strlen(str);
> >>>       size_t sfx_len = strlen(sfx);
> >>>
> >>> -     if (sfx_len <= str_len)
> >>> -             return strcmp(str + str_len - sfx_len, sfx);
> >>> -     return false;
> >>> +     if (sfx_len > str_len)
> >>> +             return false;
> >>> +     return strcmp(str + str_len - sfx_len, sfx) == 0;
> >> Please tag the subject with "bpf" next time.
> >>
> >> Acked-by: Martin KaFai Lau <kafai@fb.com>
> >
> > Alan,
> >
> > If it was so broken how did it work earlier?
> > Do we have a test for this?
> >
>
> We have tests for automatic path determination, yes, but those
> tests specify libc.so.6, so are testing the strstr(file, ".so.")
> predicate below:
>
>         if (str_has_sfx(file, ".so") || strstr(file, ".so.")) {
>
> Problem is, on many systems, libc.so is a GNU ld script rather
> than an actual library:
>
> cat /usr/lib64/libc.so
> /* GNU ld script
>    Use the shared library, but some functions are only in
>    the static library, so try that secondarily.  */
> OUTPUT_FORMAT(elf64-x86-64)
> GROUP ( /lib64/libc.so.6 /usr/lib64/libc_nonshared.a  AS_NEEDED ( /lib64/ld-linux-x86-64.so.2 ) )
>
> ...so we can't rely on system library .so files actually containing
> the library to instrument.
>
> Maybe we can do something with liburandom_read.so now we have it
> there; I was looking at extending the auto-path determination
> to usdt too, so we could add a new test to cover this then I think.

Library path resolution should already work for USDTs (note that I
reuse resolve_full_path() in bpf_program__attach_usdt()), but having
explicit tests would be great. It might be simplest to temporarily
override LD_LIBRARY_PATH with a path to liburandom_read.so? So please
consider sending a patch with tests, thanks!

>
> Alan

Re: [PATCH] libbpf: fix str_has_sfx()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Tue, 19 Jul 2022 12:53:01 +0300 you wrote:
> The return from strcmp() is inverted so the it returns true instead
> of false and vise versa.
> 
> Fixes: a1c9d61b19cb ("libbpf: Improve library identification for uprobe binary path resolution")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> Spotted during review.  *cmp() functions should always have a comparison
> to zero.
> 	if (strcmp(a, b) < 0) {  <-- means a < b
> 	if (strcmp(a, b) >= 0) { <-- means a >= b
> 	if (strcmp(a, b) != 0) { <-- means a != b
> etc.
> 
> [...]

Here is the summary with links:
  - libbpf: fix str_has_sfx()
    https://git.kernel.org/bpf/bpf-next/c/14229b8153a3

You are awesome, thank you!
-- 
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