bpf: Fix bpf_strtol and bpf_strtoul helpers for 32bit

The bpf_strtol() and bpf_strtoul() helpers are currently broken on 32bit:

The argument type ARG_PTR_TO_LONG is BPF-side "long", not kernel-side "long"
and therefore always considered fixed 64bit no matter if 64 or 32bit underlying
architecture.

This contract breaks in case of the two mentioned helpers since their BPF_CALL
definition for the helpers was added with {unsigned,}long *res. Meaning, the
transition from BPF-side "long" (BPF program) to kernel-side "long" (BPF helper)
breaks here.

Both helpers call __bpf_strtoll() with "long long" correctly, but later assigning
the result into 32-bit "*(long *)" on 32bit architectures. From a BPF program
point of view, this means upper bits will be seen as uninitialised.

Therefore, fix both BPF_CALL signatures to {s,u}64 types to fix this situation.

Now, changing also uapi/bpf.h helper documentation which generates bpf_helper_defs.h
for BPF programs is tricky: Changing signatures there to __{s,u}64 would trigger
compiler warnings (incompatible pointer types passing 'long *' to parameter of type
'__s64 *' (aka 'long long *')) for existing BPF programs.

Leaving the signatures as-is would be fine as from BPF program point of view it is
still BPF-side "long" and thus equivalent to __{s,u}64 on 64 or 32bit underlying
architectures.

Note that bpf_strtol() and bpf_strtoul() are the only helpers with this issue.

Fixes: d7a4cb9 ("bpf: Introduce bpf_strtol and bpf_strtoul helpers")
Reported-by: Alexei Starovoitov <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: borkmann

kernel/bpf/helpers.c

@@ -518,7 +518,7 @@ static int __bpf_strtoll(const char *buf, size_t buf_len, u64 flags,
 }
 
 BPF_CALL_4(bpf_strtol, const char *, buf, size_t, buf_len, u64, flags,
-	   long *, res)
+	   s64 *, res)
 {
 	long long _res;
 	int err;
@@ -543,7 +543,7 @@ const struct bpf_func_proto bpf_strtol_proto = {
 };
 
 BPF_CALL_4(bpf_strtoul, const char *, buf, size_t, buf_len, u64, flags,
-	   unsigned long *, res)
+	   u64 *, res)
 {
 	unsigned long long _res;
 	bool is_negative;