[PATCH 5.15 141/244] net: genl: fix error path memory leak in policy dumping

Greg Kroah-Hartman
2022-08-23T10:15:08Z

From: Jakub Kicinski <kuba@kernel.org>

commit 249801360db3dec4f73768c502192020bfddeacc upstream.

If construction of the array of policies fails when recording
non-first policy we need to unwind.

netlink_policy_dump_add_policy() itself also needs fixing as
it currently gives up on error without recording the allocated
pointer in the pstate pointer.

Reported-by: syzbot+dc54d9ba8153b216cae0@syzkaller.appspotmail.com
Fixes: 50a896cf2d6f ("genetlink: properly support per-op policy dumping")
Link: https://lore.kernel.org/r/20220816161939.577583-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/netlink/genetlink.c | 6 +++++-
net/netlink/policy.c | 14 ++++++++++++--
2 files changed, 17 insertions(+), 3 deletions(-)

--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -1174,13 +1174,17 @@ static int ctrl_dumppolicy_start(struct
op.policy,
op.maxattr);
if (err)
- return err;
+ goto err_free_state;
}
}

if (!ctx->state)
return -ENODATA;
return 0;
+
+err_free_state:
+ netlink_policy_dump_free(ctx->state);
+ return err;
}

static void *ctrl_dumppolicy_prep(struct sk_buff *skb,
--- a/net/netlink/policy.c
+++ b/net/netlink/policy.c
@@ -144,7 +144,7 @@ int netlink_policy_dump_add_policy(struc

err = add_policy(&state, policy, maxtype);
if (err)
- return err;
+ goto err_try_undo;

for (policy_idx = 0;
policy_idx < state->n_alloc && state->policies[policy_idx].policy;
@@ -164,7 +164,7 @@ int netlink_policy_dump_add_policy(struc
policy[type].nested_policy,
policy[type].len);
if (err)
- return err;
+ goto err_try_undo;
break;
default:
break;
@@ -174,6 +174,16 @@ int netlink_policy_dump_add_policy(struc

*pstate = state;
return 0;
+
+err_try_undo:
+ /* Try to preserve reasonable unwind semantics - if we're starting from
+ * scratch clean up fully, otherwise record what we got and caller will.
+ */
+ if (!*pstate)
+ netlink_policy_dump_free(state);
+ else
+ *pstate = state;
+ return err;
}

static bool