[PATCH 5/5] bpf: Check correct cred for CAP_SYSLOG in bpf_dump_raw_ok()

Kees Cook
2020-07-02T23:27:05Z

When evaluating access control over kallsyms visibility, credentials at
open() time need to be used, not the "current" creds (though in BPF's
case, this has likely always been the same). Plumb access to associated
file->f_cred down through bpf_dump_raw_ok() and its callers now that
kallsysm_show_value() has been refactored to take struct cred.

Cc: stable@vger.kernel.org
Fixes: 7105e828c087 ("bpf: allow for correlation of maps and helpers in dump")
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/filter.h | 4 ++--
kernel/bpf/syscall.c | 37 +++++++++++++++++++++----------------
net/core/sysctl_net_core.c | 2 +-
3 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 55104f6c78e8..0b0144752d78 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -884,12 +884,12 @@ void bpf_jit_compile(struct bpf_prog *prog);
bool bpf_jit_needs_zext(void);
bool bpf_helper_changes_pkt_data(void *func);

-static inline bool bpf_dump_raw_ok(void)
+static inline bool bpf_dump_raw_ok(const struct cred *cred)
{
/* Reconstruction of call-sites is dependent on kallsyms,
* thus make dump the same restriction.
*/
- return kallsyms_show_value(current_cred());
+ return kallsyms_show_value(cred);
}

struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8da159936bab..859053ddf05b 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3139,7 +3139,8 @@ static const struct bpf_map *bpf_map_from_imm(const struct bpf_prog *prog,
return NULL;
}

-static struct bpf_insn *bpf_insn_prepare_dump(const struct bpf_prog *prog)
+static struct bpf_insn *bpf_insn_prepare_dump(const struct bpf_prog *prog,
+ const struct cred *f_cred)
{
const struct bpf_map *map;
struct bpf_insn *insns;
@@ -3165,7 +3166,7 @@ static struct bpf_insn *bpf_insn_prepare_dump(const struct bpf_prog *prog)
code == (BPF_JMP | BPF_CALL_ARGS)) {
if (code == (BPF_JMP | BPF_CALL_ARGS))
insns[i].code = BPF_JMP | BPF_CALL;
- if (!bpf_dump_raw_ok())
+ if (!bpf_dump_raw_ok(f_cred))
insns[i].imm = 0;
continue;
}
@@ -3221,7 +3222,8 @@ static int set_info_rec_size(struct bpf_prog_info *info)
return 0;
}

-static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
+static int bpf_prog_get_info_by_fd(struct file *file,
+ struct bpf_prog *prog,
const union bpf_attr *attr,
union bpf_attr __user *uattr)
{
@@ -3290,11 +3292,11 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
struct bpf_insn *insns_sanitized;
bool fault;

- if (prog->blinded && !bpf_dump_raw_ok()) {
+ if (prog->blinded && !bpf_dump_raw_ok(file->f_cred)) {
info.xlated_prog_insns = 0;
goto done;
}
- insns_sanitized = bpf_insn_prepare_dump(prog);
+ insns_sanitized = bpf_insn_prepare_dump(prog, file->f_cred);
if (!insns_sanitized)
return -ENOMEM;
uinsns = u64_to_user_ptr(info.xlated_prog_insns);
@@ -3328,7 +3330,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
}

if (info.jited_prog_len && ulen) {
- if (bpf_dump_raw_ok()) {
+ if (bpf_dump_raw_ok(file->f_cred)) {
uinsns = u64_to_user_ptr(info.jited_prog_insns);
ulen = min_t(u32, info.jited_prog_len, ulen);

@@ -3363,7 +3365,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
ulen = info.nr_jited_ksyms;
info.nr_jited_ksyms = prog->aux->func_cnt ? : 1;
if (ulen) {
- if (bpf_dump_raw_ok()) {
+ if (bpf_dump_raw_ok(file->f_cred)) {
unsigned long ksym_addr;
u64 __user *user_ksyms;
u32 i;
@@ -3394,7 +3396,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
ulen = info.nr_jited_func_lens;
info.nr_jited_func_lens = prog->aux->func_cnt ? : 1;
if (ulen) {
- if (bpf_dump_raw_ok()) {
+ if (bpf_dump_raw_ok(file->f_cred)) {
u32 __user *user_lens;
u32 func_len, i;

@@ -3451,7 +3453,7 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
else
info.nr_jited_line_info = 0;
if (info.nr_jited_line_info && ulen) {
- if (bpf_dump_raw_ok()) {
+ if (bpf_dump_raw_ok(file->f_cred)) {
__u64 __user *user_linfo;
u32 i;

@@ -3497,7 +3499,8 @@ static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
return 0;
}

-static int bpf_map_get_info_by_fd(struct bpf_map *map,
+static int bpf_map_get_info_by_fd(struct file *file,
+ struct bpf_map *map,
const union bpf_attr *attr,
union bpf_attr __user *uattr)
{
@@ -3540,7 +3543,8 @@ static int bpf_map_get_info_by_fd(struct bpf_map *map,
return 0;
}

-static int bpf_btf_get_info_by_fd(struct btf *btf,
+static int bpf_btf_get_info_by_fd(struct file *file,
+ struct btf *btf,
const union bpf_attr *attr,
union bpf_attr __user *uattr)
{
@@ -3555,7 +3559,8 @@ static int bpf_btf_get_info_by_fd(struct btf *btf,
return btf_get_info_by_fd(btf, attr, uattr);
}

-static int bpf_link_get_info_by_fd(struct bpf_link *link,
+static int bpf_link_get_info_by_fd(struct file *file,
+ struct bpf_link *link,
const union bpf_attr *attr,
union bpf_attr __user *uattr)
{
@@ -3608,15 +3613,15 @@ static int bpf_obj_get_info_by_fd(const union bpf_attr *attr,
return -EBADFD;

if (f.file->f_op == &bpf_prog_fops)
- err = bpf_prog_get_info_by_fd(f.file->private_data, attr,
+ err = bpf_prog_get_info_by_fd(f.file, f.file->private_data, attr,
uattr);
else if (f.file->f_op == &bpf_map_fops)
- err = bpf_map_get_info_by_fd(f.file->private_data, attr,
+ err = bpf_map_get_info_by_fd(f.file, f.file->private_data, attr,
uattr);
else if (f.file->f_op == &btf_fops)
- err = bpf_btf_get_info_by_fd(f.file->private_data, attr, uattr);
+ err = bpf_btf_get_info_by_fd(f.file, f.file->private_data, attr, uattr);
else if (f.file->f_op == &bpf_link_fops)
- err = bpf_link_get_info_by_fd(f.file->private_data,
+ err = bpf_link_get_info_by_fd(f.file, f.file->private_data,
attr, uattr);
else
err = -EINVAL;
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index f93f8ace6c56..6ada114bbcca 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -274,7 +274,7 @@ static int proc_dointvec_minmax_bpf_enable(struct ctl_table *table, int write,
ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
if (write && !ret) {
if (jit_enable < 2 ||
- (jit_enable == 2 && bpf_dump_raw_ok())) {
+ (jit_enable == 2 && bpf_dump_raw_ok(current_cred()))) {
*(int *)table->data = jit_enable;
if (jit_enable == 2)
pr_warn("bpf_jit_enable = 2 was set! NEVER use this in production, only for JIT debugging!\n");
--
2.25.1