lkml.org 
[lkml]   [2019]   [Dec]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH bpf-next v1 10/13] bpf: lsm: Handle attachment of the same program
Date
From: KP Singh <kpsingh@google.com>

Allow 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.

./loader Attaches "env_dumper__v1" followed by "env_dumper__v2"
to the bprm_check_security hook..

./loader
./loader

Before:

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

After:

cat /sys/kernel/security/bpf/process_execution
env_dumper__v2

Signed-off-by: KP Singh <kpsingh@google.com>
---
security/bpf/ops.c | 57 +++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 56 insertions(+), 1 deletion(-)

diff --git a/security/bpf/ops.c b/security/bpf/ops.c
index e9aae2ce718c..481e6ee75f27 100644
--- a/security/bpf/ops.c
+++ b/security/bpf/ops.c
@@ -64,11 +64,52 @@ static struct bpf_lsm_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
+ * the matched program to be replaced by a newer version.
+ *
+ * For example:
+ *
+ * env_dumper__v1 is matched with env_dumper__v2
+ *
+ */
+static bool match_prog_name(const char *a, const char *b)
+{
+ size_t 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 bpf_lsm_attach(const union bpf_attr *attr, struct bpf_prog *prog)
{
struct bpf_prog_array *old_array;
struct bpf_prog_array *new_array;
struct bpf_lsm_hook *h;
+ struct bpf_prog *old_prog = NULL;
int ret = 0;

h = get_hook_from_fd(attr->target_fd);
@@ -78,13 +119,27 @@ int bpf_lsm_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 already exists and replace
+ * the existing program if BPF_F_ALLOW_OVERRIDE is specified in
+ * the attach flags.
+ */
+ if (old_array) {
+ 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)
goto unlock;

rcu_assign_pointer(h->progs, new_array);
bpf_prog_array_free(old_array);
+ if (old_prog)
+ bpf_prog_put(old_prog);

unlock:
mutex_unlock(&h->mutex);
--
2.20.1
\
 
 \ /
  Last update: 2019-12-20 16:43    [W:0.226 / U:3.508 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site