[PATCH] bpf: fix missing checks of the return value of check_reg_arg

[PATCH] bpf: fix missing checks of the return value of check_reg_arg

[Kangjie Lu]

check_reg_arg() may fail. This fix inserts checks for its return value.
If check_reg_arg() fails, issues an error message.

Signed-off-by: Kangjie Lu <kjlu@umn.edu>
---
 kernel/bpf/verifier.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 51ba84d4d34a..fde91a5c0b5a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2619,7 +2619,10 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 	/* after the call registers r0 - r5 were scratched */
 	for (i = 0; i < CALLER_SAVED_REGS; i++) {
 		mark_reg_not_init(env, caller->regs, caller_saved[i]);
-		check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
+		err = check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
+		if (err)
+			verbose(env,
+					"check_reg_arg() fails in setting caller saved regs\n");
 	}
 
 	/* only increment it after check_reg_arg() finished */
@@ -2842,7 +2845,10 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
 	/* reset caller saved regs */
 	for (i = 0; i < CALLER_SAVED_REGS; i++) {
 		mark_reg_not_init(env, regs, caller_saved[i]);
-		check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
+		err = check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
+		if (err)
+			verbose(env,
+				"check_reg_arg() fails in resetting caller saved regs\n");
 	}
 
 	/* update return register (already marked as written above) */
@@ -4435,7 +4441,10 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn)
 	/* reset caller saved regs to unreadable */
 	for (i = 0; i < CALLER_SAVED_REGS; i++) {
 		mark_reg_not_init(env, regs, caller_saved[i]);
-		check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
+		err = check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
+		if (err)
+			verbose(env,
+				"check_reg_arg() fails in resetting caller saved regs to unreadable\n");
 	}
 
 	/* mark destination R0 register as readable, since it contains
-- 
2.17.2 (Apple Git-113)

Re: [PATCH] bpf: fix missing checks of the return value of check_reg_arg

[Alexei Starovoitov]

On Tue, Dec 25, 2018 at 01:17:10AM -0600, Kangjie Lu wrote:
> check_reg_arg() may fail. This fix inserts checks for its return value.
> If check_reg_arg() fails, issues an error message.
> 
> Signed-off-by: Kangjie Lu <kjlu@umn.edu>
> ---
>  kernel/bpf/verifier.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 51ba84d4d34a..fde91a5c0b5a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -2619,7 +2619,10 @@ static int check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>  	/* after the call registers r0 - r5 were scratched */
>  	for (i = 0; i < CALLER_SAVED_REGS; i++) {
>  		mark_reg_not_init(env, caller->regs, caller_saved[i]);
> -		check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
> +		err = check_reg_arg(env, caller_saved[i], DST_OP_NO_MARK);
> +		if (err)
> +			verbose(env,
> +					"check_reg_arg() fails in setting caller saved regs\n");

Such patch was already posted.
These calls cannot fail.
I prefer to leave them as-is.