On Fri, Jul 26, 2024 at 1:56 AM Matt Bobrowski <mattbobrowski@xxxxxxxxxx> wrote:
>
> Add a bunch of negative selftests responsible for asserting that the
> BPF verifier successfully rejects a BPF program load when the
> underlying BPF program misuses one of the newly introduced VFS based
> BPF kfuncs.
Negative tests are great. Thanks for adding them.
A few nitpicks below.
[...]
> diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
> index 828556cdc2f0..8a1ed62b4ed1 100644
> --- a/tools/testing/selftests/bpf/bpf_experimental.h
> +++ b/tools/testing/selftests/bpf/bpf_experimental.h
> @@ -195,6 +195,32 @@ extern void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it) __ksym;
> */
> extern void bpf_throw(u64 cookie) __ksym;
>
> +/* Description
> + * Acquire a reference on the exe_file member field belonging to the
> + * mm_struct that is nested within the supplied task_struct. The supplied
> + * task_struct must be trusted/referenced.
> + * Returns
> + * A referenced file pointer pointing to the exe_file member field of the
> + * mm_struct nested in the supplied task_struct, or NULL.
> + */
> +extern struct file *bpf_get_task_exe_file(struct task_struct *task) __ksym;
> +
> +/* Description
> + * Release a reference on the supplied file. The supplied file must be
> + * trusted/referenced.
Probably replace "trusted/referenced" with "acquired".
> + */
> +extern void bpf_put_file(struct file *file) __ksym;
> +
> +/* Description
> + * Resolve a pathname for the supplied path and store it in the supplied
> + * buffer. The supplied path must be trusted/referenced.
> + * Returns
> + * A positive integer corresponding to the length of the resolved pathname,
> + * including the NULL termination character, stored in the supplied
> + * buffer. On error, a negative integer is returned.
> + */
> +extern int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz) __ksym;
> +
In my environment, we already have these declarations in vmlinux.h.
So maybe we don't need to add them manually?
> /* This macro must be used to mark the exception callback corresponding to the
> * main program. For example:
> *
> diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
> index 67a49d12472c..14d74ba2188e 100644
> --- a/tools/testing/selftests/bpf/prog_tests/verifier.c
> +++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
> @@ -85,6 +85,7 @@
> #include "verifier_value_or_null.skel.h"
> #include "verifier_value_ptr_arith.skel.h"
> #include "verifier_var_off.skel.h"
> +#include "verifier_vfs_reject.skel.h"
> #include "verifier_xadd.skel.h"
> #include "verifier_xdp.skel.h"
> #include "verifier_xdp_direct_packet_access.skel.h"
> @@ -205,6 +206,7 @@ void test_verifier_value(void) { RUN(verifier_value); }
> void test_verifier_value_illegal_alu(void) { RUN(verifier_value_illegal_alu); }
> void test_verifier_value_or_null(void) { RUN(verifier_value_or_null); }
> void test_verifier_var_off(void) { RUN(verifier_var_off); }
> +void test_verifier_vfs_reject(void) { RUN(verifier_vfs_reject); }
> void test_verifier_xadd(void) { RUN(verifier_xadd); }
> void test_verifier_xdp(void) { RUN(verifier_xdp); }
> void test_verifier_xdp_direct_packet_access(void) { RUN(verifier_xdp_direct_packet_access); }
> diff --git a/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c b/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c
> new file mode 100644
> index 000000000000..27666a8ef78a
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/verifier_vfs_reject.c
> @@ -0,0 +1,196 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2024 Google LLC. */
> +
> +#include <vmlinux.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include <linux/limits.h>
> +
> +#include "bpf_misc.h"
> +#include "bpf_experimental.h"
> +
> +static char buf[PATH_MAX];
> +
> +SEC("lsm.s/file_open")
> +__failure __msg("Possibly NULL pointer passed to trusted arg0")
> +int BPF_PROG(get_task_exe_file_kfunc_null)
> +{
> + struct file *acquired;
> +
> + /* Can't pass a NULL pointer to bpf_get_task_exe_file(). */
> + acquired = bpf_get_task_exe_file(NULL);
> + if (!acquired)
> + return 0;
> +
> + bpf_put_file(acquired);
> + return 0;
> +}
> +
> +SEC("lsm.s/inode_getxattr")
> +__failure __msg("arg#0 pointer type STRUCT task_struct must point to scalar, or struct with scalar")
> +int BPF_PROG(get_task_exe_file_kfunc_fp)
> +{
> + u64 x;
> + struct file *acquired;
> + struct task_struct *fp;
"fp" is a weird name for a task_struct pointer.
Other than these:
Acked-by: Song Liu <song@xxxxxxxxxx>
> +
> + fp = (struct task_struct *)&x;
> + /* Can't pass random frame pointer to bpf_get_task_exe_file(). */
> + acquired = bpf_get_task_exe_file(fp);
> + if (!acquired)
> + return 0;
> +
> + bpf_put_file(acquired);
> + return 0;
> +}
> +
[...]
