perf augmented_syscalls: Check probe_read_str() return separately

Using a value returned from probe_read_str() to tell how many bytes to
copy using perf_event_output() has issues in some older kernels, like
4.17.17-100.fc27.x86_64, so separate the bounds checking done on how
many bytes to copy to a separate variable, so that the next patch has
only what is being done to make the test pass on older BPF validators.

For reference, see the discussion in this thread:

  https://www.spinics.net/lists/netdev/msg480099.html

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Yonghong Song <yhs@fb.com>
Link: https://lkml.kernel.org/n/tip-jtsapwibyxrnv1xjfsgzp0fj@git.kernel.orgSigned-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 58094c48
......@@ -33,9 +33,9 @@ struct syscall_exit_args {
};
struct augmented_filename {
int size;
int reserved;
char value[256];
unsigned int size;
int reserved;
char value[256];
};
#define augmented_filename_syscall(syscall) \
......@@ -46,14 +46,15 @@ struct augmented_enter_##syscall##_args { \
int syscall_enter(syscall)(struct syscall_enter_##syscall##_args *args) \
{ \
struct augmented_enter_##syscall##_args augmented_args = { .filename.reserved = 0, }; \
unsigned int len = sizeof(augmented_args); \
probe_read(&augmented_args.args, sizeof(augmented_args.args), args); \
augmented_args.filename.size = probe_read_str(&augmented_args.filename.value, \
sizeof(augmented_args.filename.value), \
args->filename_ptr); \
if (augmented_args.filename.size < sizeof(augmented_args.filename.value)) \
len -= sizeof(augmented_args.filename.value) - augmented_args.filename.size; \
perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, \
&augmented_args, \
(sizeof(augmented_args) - sizeof(augmented_args.filename.value) + \
augmented_args.filename.size)); \
&augmented_args, len); \
return 0; \
} \
int syscall_exit(syscall)(struct syscall_exit_args *args) \
......
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