On Sat, Apr 24, 2021 at 12:38 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Mon, Apr 19, 2021 at 8:52 AM Florent Revest <revest@xxxxxxxxxxxx> wrote:
> >
> > The "positive" part tests all format specifiers when things go well.
> >
> > The "negative" part makes sure that incorrect format strings fail at
> > load time.
> >
> > Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
> > ---
> > .../selftests/bpf/prog_tests/snprintf.c | 125 ++++++++++++++++++
> > .../selftests/bpf/progs/test_snprintf.c | 73 ++++++++++
> > .../bpf/progs/test_snprintf_single.c | 20 +++
> > 3 files changed, 218 insertions(+)
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf.c
> > create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf.c
> > create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf_single.c
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/snprintf.c b/tools/testing/selftests/bpf/prog_tests/snprintf.c
> > new file mode 100644
> > index 000000000000..a958c22aec75
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/snprintf.c
> > @@ -0,0 +1,125 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2021 Google LLC. */
> > +
> > +#include <test_progs.h>
> > +#include "test_snprintf.skel.h"
> > +#include "test_snprintf_single.skel.h"
> > +
> > +#define EXP_NUM_OUT "-8 9 96 -424242 1337 DABBAD00"
> > +#define EXP_NUM_RET sizeof(EXP_NUM_OUT)
> > +
> > +#define EXP_IP_OUT "127.000.000.001 0000:0000:0000:0000:0000:0000:0000:0001"
> > +#define EXP_IP_RET sizeof(EXP_IP_OUT)
> > +
> > +/* The third specifier, %pB, depends on compiler inlining so don't check it */
> > +#define EXP_SYM_OUT "schedule schedule+0x0/"
> > +#define MIN_SYM_RET sizeof(EXP_SYM_OUT)
> > +
> > +/* The third specifier, %p, is a hashed pointer which changes on every reboot */
> > +#define EXP_ADDR_OUT "0000000000000000 ffff00000add4e55 "
> > +#define EXP_ADDR_RET sizeof(EXP_ADDR_OUT "unknownhashedptr")
> > +
> > +#define EXP_STR_OUT "str1 longstr"
> > +#define EXP_STR_RET sizeof(EXP_STR_OUT)
> > +
> > +#define EXP_OVER_OUT "%over"
> > +#define EXP_OVER_RET 10
> > +
> > +#define EXP_PAD_OUT " 4 000"
>
> Roughly 50% of the time I get failure for this test case:
>
> test_snprintf_positive:FAIL:pad_out unexpected pad_out: actual ' 4
> 0000' != expected ' 4 000'
>
> Re-running this test case immediately passes. Running again most
> probably fails. Please take a look.
Do you have more information on how to reproduce this ?
I spinned up a VM at 87bd9e602 with ./vmtest -s and then run this script:
#!/bin/sh
for i in `seq 1000`
do
./test_progs -t snprintf
if [ $? -ne 0 ];
then
echo FAILURE
exit 1
fi
done
The thousand executions passed.
This is a bit concerning because your unexpected_pad_out seems to have
an extra '0' so it ends up with strlen(pad_out)=11 but
sizeof(pad_out)=10. The actual string writing is not really done by
our helper code but by the snprintf implementation (str and str_size
are only given to snprintf()) so I'd expect the truncation to work
well there. I'm a bit puzzled
