diff mbox series

[bpf,2/3] bpf: Fix print_reg_state's constant scalar dump

Message ID 20241016134913.32249-2-daniel@iogearbox.net (mailing list archive)
State Accepted
Commit 3e9e708757ca3b7eb65a820031d62fea1a265709
Delegated to: BPF
Headers show
Series [bpf,1/3] bpf: Fix incorrect delta propagation between linked registers | expand

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Commit Message

Daniel Borkmann Oct. 16, 2024, 1:49 p.m. UTC 
print_reg_state() should not consider adding reg->off to reg->var_off.value
when dumping scalars. Scalars can be produced with reg->off != 0 through
BPF_ADD_CONST, and thus as-is this can skew the register log dump.

Fixes: 98d7ca374ba4 ("bpf: Track delta between "linked" registers.")
Reported-by: Nathaniel Theis <nathaniel.theis@nccgroup.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/log.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

Andrii Nakryiko Oct. 16, 2024, 8:16 p.m. UTC | #1 
On Wed, Oct 16, 2024 at 6:49 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> print_reg_state() should not consider adding reg->off to reg->var_off.value
> when dumping scalars. Scalars can be produced with reg->off != 0 through
> BPF_ADD_CONST, and thus as-is this can skew the register log dump.
>
> Fixes: 98d7ca374ba4 ("bpf: Track delta between "linked" registers.")
> Reported-by: Nathaniel Theis <nathaniel.theis@nccgroup.com>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> ---
>  kernel/bpf/log.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
> index 5aebfc3051e3..4a858fdb6476 100644
> --- a/kernel/bpf/log.c
> +++ b/kernel/bpf/log.c
> @@ -688,8 +688,7 @@ static void print_reg_state(struct bpf_verifier_env *env,
>         if (t == SCALAR_VALUE && reg->precise)
>                 verbose(env, "P");
>         if (t == SCALAR_VALUE && tnum_is_const(reg->var_off)) {
> -               /* reg->off should be 0 for SCALAR_VALUE */
> -               verbose_snum(env, reg->var_off.value + reg->off);
> +               verbose_snum(env, reg->var_off.value);
>                 return;

The original code was handling SCALAR_VALUE and PTR_TO_STACK cases, so
`+ reg->off` under assumption of reg->off being zero for SCALAR_VALUE
case made sense. Now this is a SCALAR_VALUE-only code path, so there
is no point in doing this.

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>         }
>
> --
> 2.43.0
>
diff mbox series

Patch

diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
index 5aebfc3051e3..4a858fdb6476 100644
--- a/kernel/bpf/log.c
+++ b/kernel/bpf/log.c
@@ -688,8 +688,7 @@  static void print_reg_state(struct bpf_verifier_env *env,
 	if (t == SCALAR_VALUE && reg->precise)
 		verbose(env, "P");
 	if (t == SCALAR_VALUE && tnum_is_const(reg->var_off)) {
-		/* reg->off should be 0 for SCALAR_VALUE */
-		verbose_snum(env, reg->var_off.value + reg->off);
+		verbose_snum(env, reg->var_off.value);
 		return;
 	}