[PATCH 5.10 05/43] bpf: Fix signed_{sub,add32}_overflows type handling

Greg Kroah-Hartman
2021-01-22T14:57:58Z

From: Daniel Borkmann <daniel@iogearbox.net>

commit bc895e8b2a64e502fbba72748d59618272052a8b upstream.

Fix incorrect signed_{sub,add32}_overflows() input types (and a related buggy
comment). It looks like this might have slipped in via copy/paste issue, also
given prior to 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
the signature of signed_sub_overflows() had s64 a and s64 b as its input args
whereas now they are truncated to s32. Thus restore proper types. Also, the case
of signed_add32_overflows() is not consistent to signed_sub32_overflows(). Both
have s32 as inputs, therefore align the former.

Fixes: 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking")
Reported-by: De4dCr0w <sa516203@mail.ustc.edu.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/bpf/verifier.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5255,7 +5255,7 @@ static bool signed_add_overflows(s64 a,
return res < a;
}

-static bool signed_add32_overflows(s64 a, s64 b)
+static bool signed_add32_overflows(s32 a, s32 b)
{
/* Do the add in u32, where overflow is well-defined */
s32 res = (s32)((u32)a + (u32)b);
@@ -5265,7 +5265,7 @@ static bool signed_add32_overflows(s64 a
return res < a;
}

-static bool signed_sub_overflows(s32 a, s32 b)
+static bool signed_sub_overflows(s64 a, s64 b)
{
/* Do the sub in u64, where overflow is well-defined */
s64 res = (s64)((u64)a - (u64)b);
@@ -5277,7 +5277,7 @@ static bool signed_sub_overflows(s32 a,

static bool signed_sub32_overflows(s32 a, s32 b)
{
- /* Do the sub in u64, where overflow is well-defined */
+ /* Do the sub in u32, where overflow is well-defined */
s32 res = (s32)((u32)a - (u32)b);

if (b < 0)