Re: [PATCH 2/2] bpf: Implement kretprobe fallback for kprobe multi link

[bot+bpf-ci@kernel.org]

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> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 1fd07c10378f..426a1c627508 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c

[ ... ]

> +int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> +{
> +	struct bpf_kprobe_multi_link *link = NULL;
> +	struct bpf_link_primer link_primer;
> +	struct bpf_kprobe *kprobes = NULL;
> +	u32 flags, cnt;
> +	u64 __user *ucookies;
> +	unsigned long __user *uaddrs;
> +	unsigned long __user *usyms;
> +	int err, i;

[ ... ]

> +	for (i = 0; i < cnt; i++) {
> +		unsigned long addr;
> +
> +		if (uaddrs) {
> +			if (__get_user(addr, uaddrs + i)) {
> +				err = -EFAULT;
> +				goto error;
> +			}
> +		} else {
> +			unsigned long __user usymbol;
> +			char buf[KSYM_NAME_LEN];
> +
> +			if (__get_user(usymbol, usyms + i)) {
> +				err = -EFAULT;
> +				goto error;
> +			}
> +			err = strncpy_from_user(buf, (const char __user *) usymbol, KSYM_NAME_LEN);
> +			if (err == KSYM_NAME_LEN)
> +				err = -E2BIG;
> +			if (err < 0)
> +				goto error;
> +
> +			addr = kallsyms_lookup_name(buf);
> +			if (!addr)
> +				goto error;

When kallsyms_lookup_name() returns 0 (symbol not found), is err being set
to an error code before jumping to the error label? It looks like err will
still hold the positive return value from strncpy_from_user() (the string
length), which would be returned to the caller as a success indication.

The error label at the end of the function does:

    error:
        kvfree(kprobes);
        kfree(link);
        return err;

This could cause the syscall to return a positive value to userspace instead
of an error, and also leak a prog reference since link_create() only calls
bpf_prog_put() when ret < 0.

> +		}
> +		if (prog->kprobe_override && !within_error_injection_list(addr)) {
> +			err = -EINVAL;
> +			goto error;
> +		}

[ ... ]


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/20338242683