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: d7a4cb9b6705 ("bpf: Introduce bpf_strtol and bpf_strtoul helpers")
Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/481fcec8-c12c-9abb-8ecb-76c71c009959@xxxxxxxxxxxxx
---
v3 -> v4:
- added patch
kernel/bpf/helpers.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3956be5d6440..0cf42be52890 100644
--- a/kernel/bpf/helpers.c
+++ b/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;
--
2.43.0
