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Subject[RFC v1 10/14] krsi: Handle attachment of the same program
Date
From: KP Singh <kpsingh@google.com>

Allow the userspace to attach a newer version of a program without
having duplicates of the same program.

If BPF_F_ALLOW_OVERRIDE is passed, the attachment logic compares the
name of the new program to the names of existing attached programs. The
names are only compared till a "__" (or '\0', if there is no "__"). If
a successful match is found, the existing program is replaced with the
newer attachment.

./krsi Attaches "env_dumper__v1" followed by "env_dumper__v2"
to the process_execution hook of the KRSI LSM.

./krsi
./krsi

Before:

cat /sys/kernel/security/krsi/process_execution
env_dumper__v1
env_dumper__v2

After:

cat /sys/kernel/security/krsi/process_execution
env_dumper__v2

Signed-off-by: KP Singh <kpsingh@google.com>
---
security/krsi/ops.c | 53 ++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/security/krsi/ops.c b/security/krsi/ops.c
index 57bd304a03f4..1f4df920139c 100644
--- a/security/krsi/ops.c
+++ b/security/krsi/ops.c
@@ -65,11 +65,52 @@ static struct krsi_hook *get_hook_from_fd(int fd)
return ERR_PTR(ret);
}

+/*
+ * match_prog_name matches the name of the program till "__"
+ * or the end of the string is encountered. This allows
+ * a different version of the same program to be loaded.
+ *
+ * For example:
+ *
+ * env_dumper__v1 is matched with env_dumper__v2
+ *
+ */
+static bool match_prog_name(char *a, char *b)
+{
+ int m, n;
+ char *end;
+
+ end = strstr(a, "__");
+ n = end ? end - a : strlen(a);
+
+ end = strstr(b, "__");
+ m = end ? end - b : strlen(b);
+
+ if (m != n)
+ return false;
+
+ return strncmp(a, b, n) == 0;
+}
+
+static struct bpf_prog *find_attached_prog(struct bpf_prog_array *array,
+ struct bpf_prog *prog)
+{
+ struct bpf_prog_array_item *item = array->items;
+
+ for (; item->prog; item++) {
+ if (match_prog_name(item->prog->aux->name, prog->aux->name))
+ return item->prog;
+ }
+
+ return NULL;
+}
+
int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
{
struct bpf_prog_array *old_array;
struct bpf_prog_array *new_array;
struct krsi_hook *h;
+ struct bpf_prog *old_prog;
int ret = 0;

h = get_hook_from_fd(attr->target_fd);
@@ -79,8 +120,18 @@ int krsi_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
mutex_lock(&h->mutex);
old_array = rcu_dereference_protected(h->progs,
lockdep_is_held(&h->mutex));
+ /*
+ * Check if a matching program with already exists and replace
+ * the existing program will be overridden if BPF_F_ALLOW_OVERRIDE
+ * is specified in the attach flags.
+ */
+ old_prog = find_attached_prog(old_array, prog);
+ if (old_prog && !(attr->attach_flags & BPF_F_ALLOW_OVERRIDE)) {
+ ret = -EEXIST;
+ goto unlock;
+ }

- ret = bpf_prog_array_copy(old_array, NULL, prog, &new_array);
+ ret = bpf_prog_array_copy(old_array, old_prog, prog, &new_array);
if (ret < 0) {
ret = -ENOMEM;
goto unlock;
--
2.20.1
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