2021-04-24 22:18:00

by Pedro Tammela

Subject: [PATCH bpf-next] libbpf: handle ENOTSUPP errno in libbpf_strerror()

The 'bpf()' syscall is leaking the ENOTSUPP errno that is internal to the kernel[1].
More recent code is already using the correct EOPNOTSUPP, but changing
older return codes is not possible due to dependency concerns, so handle ENOTSUPP
in libbpf_strerror().

[1] https://lore.kernel.org/netdev/[email protected]/

Signed-off-by: Pedro Tammela <[email protected]>
---
tools/lib/bpf/libbpf_errno.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/tools/lib/bpf/libbpf_errno.c b/tools/lib/bpf/libbpf_errno.c
index 0afb51f7a919..7de8bbc34a37 100644
--- a/tools/lib/bpf/libbpf_errno.c
+++ b/tools/lib/bpf/libbpf_errno.c
@@ -13,6 +13,9 @@

#include "libbpf.h"

+/* This errno is internal to the kernel but leaks in the bpf() syscall. */
+#define ENOTSUPP 524
+
/* make sure libbpf doesn't use kernel-only integer typedefs */
#pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64

@@ -43,6 +46,12 @@ int libbpf_strerror(int err, char *buf, size_t size)

err = err > 0 ? err : -err;

+ if (err == ENOTSUPP) {
+ snprintf(buf, size, "Operation not supported");
+ buf[size - 1] = '\0';
+ return 0;
+ }
+
if (err < __LIBBPF_ERRNO__START) {
int ret;

--
2.25.1

2021-04-27 16:28:03

by Daniel Borkmann

Subject: Re: [PATCH bpf-next] libbpf: handle ENOTSUPP errno in libbpf_strerror()

On 4/25/21 12:16 AM, Pedro Tammela wrote:
> The 'bpf()' syscall is leaking the ENOTSUPP errno that is internal to the kernel[1].
> More recent code is already using the correct EOPNOTSUPP, but changing
> older return codes is not possible due to dependency concerns, so handle ENOTSUPP
> in libbpf_strerror().
>
> [1] https://lore.kernel.org/netdev/[email protected]/
>
> Signed-off-by: Pedro Tammela <[email protected]>
> ---
> tools/lib/bpf/libbpf_errno.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf_errno.c b/tools/lib/bpf/libbpf_errno.c
> index 0afb51f7a919..7de8bbc34a37 100644
> --- a/tools/lib/bpf/libbpf_errno.c
> +++ b/tools/lib/bpf/libbpf_errno.c
> @@ -13,6 +13,9 @@
>
> #include "libbpf.h"
>
> +/* This errno is internal to the kernel but leaks in the bpf() syscall. */
> +#define ENOTSUPP 524
> +
> /* make sure libbpf doesn't use kernel-only integer typedefs */
> #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64
>
> @@ -43,6 +46,12 @@ int libbpf_strerror(int err, char *buf, size_t size)
>
> err = err > 0 ? err : -err;
>
> + if (err == ENOTSUPP) {
> + snprintf(buf, size, "Operation not supported");
> + buf[size - 1] = '\0';
> + return 0;
> + }
> +
> if (err < __LIBBPF_ERRNO__START) {
> int ret;

Could you fold this into the __LIBBPF_ERRNO__START test body to denote that it
belongs outside the libbpf error range? For example, could be simplified like this:

if (err < __LIBBPF_ERRNO__START) {
int ret;

/* Handle ENOTSUPP separate here given it's kernel internal,
* but for sake of error string it has the same meaning as
* the EOPNOTSUPP error.
*/
if (err == ENOTSUPP)
err = EOPNOTSUPP;
ret = strerror_r(err, buf, size);
buf[size - 1] = '\0';
return ret;
}

Thanks,
Daniel

2021-04-30 14:17:58

by Pedro Tammela

Subject: Re: [PATCH bpf-next] libbpf: handle ENOTSUPP errno in libbpf_strerror()

Em ter., 27 de abr. de 2021 às 13:18, Daniel Borkmann
<[email protected]> escreveu:
>
> On 4/25/21 12:16 AM, Pedro Tammela wrote:
> > The 'bpf()' syscall is leaking the ENOTSUPP errno that is internal to the kernel[1].
> > More recent code is already using the correct EOPNOTSUPP, but changing
> > older return codes is not possible due to dependency concerns, so handle ENOTSUPP
> > in libbpf_strerror().
> >
> > [1] https://lore.kernel.org/netdev/[email protected]/
> >
> > Signed-off-by: Pedro Tammela <[email protected]>
> > ---
> > tools/lib/bpf/libbpf_errno.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/tools/lib/bpf/libbpf_errno.c b/tools/lib/bpf/libbpf_errno.c
> > index 0afb51f7a919..7de8bbc34a37 100644
> > --- a/tools/lib/bpf/libbpf_errno.c
> > +++ b/tools/lib/bpf/libbpf_errno.c
> > @@ -13,6 +13,9 @@
> >
> > #include "libbpf.h"
> >
> > +/* This errno is internal to the kernel but leaks in the bpf() syscall. */
> > +#define ENOTSUPP 524
> > +
> > /* make sure libbpf doesn't use kernel-only integer typedefs */
> > #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64
> >
> > @@ -43,6 +46,12 @@ int libbpf_strerror(int err, char *buf, size_t size)
> >
> > err = err > 0 ? err : -err;
> >
> > + if (err == ENOTSUPP) {
> > + snprintf(buf, size, "Operation not supported");
> > + buf[size - 1] = '\0';
> > + return 0;
> > + }
> > +
> > if (err < __LIBBPF_ERRNO__START) {
> > int ret;
>
> Could you fold this into the __LIBBPF_ERRNO__START test body to denote that it
> belongs outside the libbpf error range? For example, could be simplified like this:
>
> if (err < __LIBBPF_ERRNO__START) {
> int ret;
>
> /* Handle ENOTSUPP separate here given it's kernel internal,
> * but for sake of error string it has the same meaning as
> * the EOPNOTSUPP error.
> */
> if (err == ENOTSUPP)
> err = EOPNOTSUPP;
> ret = strerror_r(err, buf, size);
> buf[size - 1] = '\0';
> return ret;
> }
>
> Thanks,
> Daniel

Sure, looks simpler indeed.

Pedro