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bpf: Fix bpf_strtol and bpf_strtoul helpers for 32bit

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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: d7a4cb9b67 ("bpf: Introduce bpf_strtol and bpf_strtoul helpers")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/481fcec8-c12c-9abb-8ecb-76c71c009959@iogearbox.net
Link: https://lore.kernel.org/r/20240913191754.13290-1-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Daniel Borkmann 2024-09-13 21:17:46 +02:00 committed by Alexei Starovoitov
parent a18062d54a
commit cfe69c50b0
1 changed files with 2 additions and 2 deletions
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4
kernel/bpf/helpers.c
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@ -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;