bpf: Check tail zero of bpf_common_attr using offsetofend

Because of the 8-byte alignment, the compiler will pad struct
bpf_common_attr to 24 bytes. That said, sizeof(attr_common) is 24 instead
of 20.

When check tail zero using sizeof(attr_common) in
bpf_check_uarg_tail_zero(), there will be 4 bytes that won't be checked.

To also check the padding 4 bytes, replace sizeof(attr_common) with
offsetofend(struct bpf_common_attr, log_true_size).

Fixes: f28771c0691b ("bpf: Extend BPF syscall with common attributes support")
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20260518145446.6794-2-leon.hwang@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6600e126fbfb4d6fea8e83c7fe107abd69cd1ac3..83de8fb9b9aaff72cc52cef1f870c78190cb382f 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -6278,7 +6278,9 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size,
 
        memset(&attr_common, 0, sizeof(attr_common));
        if (cmd & BPF_COMMON_ATTRS) {
-               err = bpf_check_uarg_tail_zero(uattr_common, sizeof(attr_common), size_common);
+               err = bpf_check_uarg_tail_zero(uattr_common,
+                                              offsetofend(struct bpf_common_attr, log_true_size),
+                                              size_common);
                if (err)
                        return err;