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Subject[PATCH v2] binder: create node flag to request sender's security context
Date
To allow servers to verify client identity, allow a node
flag to be set that causes the sender's security context
to be delivered with the transaction. The BR_TRANSACTION
command is extended in BR_TRANSACTION_SEC_CTX to
contain a pointer to the security context string.

Signed-off-by: Todd Kjos <tkjos@google.com>
---
v2: fix 32-bit build warning

drivers/android/binder.c | 106 ++++++++++++++++++++++------
include/uapi/linux/android/binder.h | 19 +++++
2 files changed, 102 insertions(+), 23 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index cdfc87629efb8..c12ade0fb75c6 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -329,6 +329,8 @@ struct binder_error {
* (invariant after initialized)
* @min_priority: minimum scheduling priority
* (invariant after initialized)
+ * @txn_security_ctx: require sender's security context
+ * (invariant after initialized)
* @async_todo: list of async work items
* (protected by @proc->inner_lock)
*
@@ -365,6 +367,7 @@ struct binder_node {
* invariant after initialization
*/
u8 accept_fds:1;
+ u8 txn_security_ctx:1;
u8 min_priority;
};
bool has_async_transaction;
@@ -615,6 +618,7 @@ struct binder_transaction {
long saved_priority;
kuid_t sender_euid;
struct list_head fd_fixups;
+ binder_uintptr_t security_ctx;
/**
* @lock: protects @from, @to_proc, and @to_thread
*
@@ -1152,6 +1156,7 @@ static struct binder_node *binder_init_node_ilocked(
node->work.type = BINDER_WORK_NODE;
node->min_priority = flags & FLAT_BINDER_FLAG_PRIORITY_MASK;
node->accept_fds = !!(flags & FLAT_BINDER_FLAG_ACCEPTS_FDS);
+ node->txn_security_ctx = !!(flags & FLAT_BINDER_FLAG_TXN_SECURITY_CTX);
spin_lock_init(&node->lock);
INIT_LIST_HEAD(&node->work.entry);
INIT_LIST_HEAD(&node->async_todo);
@@ -2778,6 +2783,8 @@ static void binder_transaction(struct binder_proc *proc,
binder_size_t last_fixup_min_off = 0;
struct binder_context *context = proc->context;
int t_debug_id = atomic_inc_return(&binder_last_id);
+ char *secctx = NULL;
+ u32 secctx_sz = 0;

e = binder_transaction_log_add(&binder_transaction_log);
e->debug_id = t_debug_id;
@@ -3020,6 +3027,20 @@ static void binder_transaction(struct binder_proc *proc,
t->flags = tr->flags;
t->priority = task_nice(current);

+ if (target_node && target_node->txn_security_ctx) {
+ u32 secid;
+
+ security_task_getsecid(proc->tsk, &secid);
+ ret = security_secid_to_secctx(secid, &secctx, &secctx_sz);
+ if (ret) {
+ return_error = BR_FAILED_REPLY;
+ return_error_param = ret;
+ return_error_line = __LINE__;
+ goto err_get_secctx_failed;
+ }
+ extra_buffers_size += ALIGN(secctx_sz, sizeof(u64));
+ }
+
trace_binder_transaction(reply, t, target_node);

t->buffer = binder_alloc_new_buf(&target_proc->alloc, tr->data_size,
@@ -3036,6 +3057,19 @@ static void binder_transaction(struct binder_proc *proc,
t->buffer = NULL;
goto err_binder_alloc_buf_failed;
}
+ if (secctx) {
+ size_t buf_offset = ALIGN(tr->data_size, sizeof(void *)) +
+ ALIGN(tr->offsets_size, sizeof(void *)) +
+ ALIGN(extra_buffers_size, sizeof(void *)) -
+ ALIGN(secctx_sz, sizeof(u64));
+ char *kptr = t->buffer->data + buf_offset;
+
+ t->security_ctx = (uintptr_t)kptr +
+ binder_alloc_get_user_buffer_offset(&target_proc->alloc);
+ memcpy(kptr, secctx, secctx_sz);
+ security_release_secctx(secctx, secctx_sz);
+ secctx = NULL;
+ }
t->buffer->debug_id = t->debug_id;
t->buffer->transaction = t;
t->buffer->target_node = target_node;
@@ -3305,6 +3339,9 @@ static void binder_transaction(struct binder_proc *proc,
t->buffer->transaction = NULL;
binder_alloc_free_buf(&target_proc->alloc, t->buffer);
err_binder_alloc_buf_failed:
+ if (secctx)
+ security_release_secctx(secctx, secctx_sz);
+err_get_secctx_failed:
kfree(tcomplete);
binder_stats_deleted(BINDER_STAT_TRANSACTION_COMPLETE);
err_alloc_tcomplete_failed:
@@ -4036,11 +4073,13 @@ static int binder_thread_read(struct binder_proc *proc,

while (1) {
uint32_t cmd;
- struct binder_transaction_data tr;
+ struct binder_transaction_data_secctx tr;
+ struct binder_transaction_data *trd = &tr.transaction_data;
struct binder_work *w = NULL;
struct list_head *list = NULL;
struct binder_transaction *t = NULL;
struct binder_thread *t_from;
+ size_t trsize = sizeof(*trd);

binder_inner_proc_lock(proc);
if (!binder_worklist_empty_ilocked(&thread->todo))
@@ -4240,8 +4279,8 @@ static int binder_thread_read(struct binder_proc *proc,
if (t->buffer->target_node) {
struct binder_node *target_node = t->buffer->target_node;

- tr.target.ptr = target_node->ptr;
- tr.cookie = target_node->cookie;
+ trd->target.ptr = target_node->ptr;
+ trd->cookie = target_node->cookie;
t->saved_priority = task_nice(current);
if (t->priority < target_node->min_priority &&
!(t->flags & TF_ONE_WAY))
@@ -4251,22 +4290,23 @@ static int binder_thread_read(struct binder_proc *proc,
binder_set_nice(target_node->min_priority);
cmd = BR_TRANSACTION;
} else {
- tr.target.ptr = 0;
- tr.cookie = 0;
+ trd->target.ptr = 0;
+ trd->cookie = 0;
cmd = BR_REPLY;
}
- tr.code = t->code;
- tr.flags = t->flags;
- tr.sender_euid = from_kuid(current_user_ns(), t->sender_euid);
+ trd->code = t->code;
+ trd->flags = t->flags;
+ trd->sender_euid = from_kuid(current_user_ns(), t->sender_euid);

t_from = binder_get_txn_from(t);
if (t_from) {
struct task_struct *sender = t_from->proc->tsk;

- tr.sender_pid = task_tgid_nr_ns(sender,
- task_active_pid_ns(current));
+ trd->sender_pid =
+ task_tgid_nr_ns(sender,
+ task_active_pid_ns(current));
} else {
- tr.sender_pid = 0;
+ trd->sender_pid = 0;
}

ret = binder_apply_fd_fixups(t);
@@ -4297,15 +4337,20 @@ static int binder_thread_read(struct binder_proc *proc,
}
continue;
}
- tr.data_size = t->buffer->data_size;
- tr.offsets_size = t->buffer->offsets_size;
- tr.data.ptr.buffer = (binder_uintptr_t)
+ trd->data_size = t->buffer->data_size;
+ trd->offsets_size = t->buffer->offsets_size;
+ trd->data.ptr.buffer = (binder_uintptr_t)
((uintptr_t)t->buffer->data +
binder_alloc_get_user_buffer_offset(&proc->alloc));
- tr.data.ptr.offsets = tr.data.ptr.buffer +
+ trd->data.ptr.offsets = trd->data.ptr.buffer +
ALIGN(t->buffer->data_size,
sizeof(void *));

+ if (t->security_ctx) {
+ cmd = BR_TRANSACTION_SEC_CTX;
+ tr.secctx = t->security_ctx;
+ trsize = sizeof(tr);
+ }
if (put_user(cmd, (uint32_t __user *)ptr)) {
if (t_from)
binder_thread_dec_tmpref(t_from);
@@ -4316,7 +4361,7 @@ static int binder_thread_read(struct binder_proc *proc,
return -EFAULT;
}
ptr += sizeof(uint32_t);
- if (copy_to_user(ptr, &tr, sizeof(tr))) {
+ if (copy_to_user(ptr, &tr, trsize)) {
if (t_from)
binder_thread_dec_tmpref(t_from);

@@ -4325,7 +4370,7 @@ static int binder_thread_read(struct binder_proc *proc,

return -EFAULT;
}
- ptr += sizeof(tr);
+ ptr += trsize;

trace_binder_transaction_received(t);
binder_stat_br(proc, thread, cmd);
@@ -4333,16 +4378,18 @@ static int binder_thread_read(struct binder_proc *proc,
"%d:%d %s %d %d:%d, cmd %d size %zd-%zd ptr %016llx-%016llx\n",
proc->pid, thread->pid,
(cmd == BR_TRANSACTION) ? "BR_TRANSACTION" :
- "BR_REPLY",
+ (cmd == BR_TRANSACTION_SEC_CTX) ?
+ "BR_TRANSACTION_SEC_CTX" : "BR_REPLY",
t->debug_id, t_from ? t_from->proc->pid : 0,
t_from ? t_from->pid : 0, cmd,
t->buffer->data_size, t->buffer->offsets_size,
- (u64)tr.data.ptr.buffer, (u64)tr.data.ptr.offsets);
+ (u64)trd->data.ptr.buffer,
+ (u64)trd->data.ptr.offsets);

if (t_from)
binder_thread_dec_tmpref(t_from);
t->buffer->allow_user_free = 1;
- if (cmd == BR_TRANSACTION && !(t->flags & TF_ONE_WAY)) {
+ if (cmd != BR_REPLY && !(t->flags & TF_ONE_WAY)) {
binder_inner_proc_lock(thread->proc);
t->to_parent = thread->transaction_stack;
t->to_thread = thread;
@@ -4690,7 +4737,8 @@ static int binder_ioctl_write_read(struct file *filp,
return ret;
}

-static int binder_ioctl_set_ctx_mgr(struct file *filp)
+static int binder_ioctl_set_ctx_mgr(struct file *filp,
+ struct flat_binder_object *fbo)
{
int ret = 0;
struct binder_proc *proc = filp->private_data;
@@ -4719,7 +4767,7 @@ static int binder_ioctl_set_ctx_mgr(struct file *filp)
} else {
context->binder_context_mgr_uid = curr_euid;
}
- new_node = binder_new_node(proc, NULL);
+ new_node = binder_new_node(proc, fbo);
if (!new_node) {
ret = -ENOMEM;
goto out;
@@ -4842,8 +4890,20 @@ static long binder_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
binder_inner_proc_unlock(proc);
break;
}
+ case BINDER_SET_CONTEXT_MGR_EXT: {
+ struct flat_binder_object fbo;
+
+ if (copy_from_user(&fbo, ubuf, sizeof(fbo))) {
+ ret = -EINVAL;
+ goto err;
+ }
+ ret = binder_ioctl_set_ctx_mgr(filp, &fbo);
+ if (ret)
+ goto err;
+ break;
+ }
case BINDER_SET_CONTEXT_MGR:
- ret = binder_ioctl_set_ctx_mgr(filp);
+ ret = binder_ioctl_set_ctx_mgr(filp, NULL);
if (ret)
goto err;
break;
diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
index b9ba520f7e4bb..2832134e53971 100644
--- a/include/uapi/linux/android/binder.h
+++ b/include/uapi/linux/android/binder.h
@@ -41,6 +41,14 @@ enum {
enum {
FLAT_BINDER_FLAG_PRIORITY_MASK = 0xff,
FLAT_BINDER_FLAG_ACCEPTS_FDS = 0x100,
+
+ /**
+ * @FLAT_BINDER_FLAG_TXN_SECURITY_CTX: request security contexts
+ *
+ * Only when set, causes senders to include their security
+ * context
+ */
+ FLAT_BINDER_FLAG_TXN_SECURITY_CTX = 0x1000,
};

#ifdef BINDER_IPC_32BIT
@@ -218,6 +226,7 @@ struct binder_node_info_for_ref {
#define BINDER_VERSION _IOWR('b', 9, struct binder_version)
#define BINDER_GET_NODE_DEBUG_INFO _IOWR('b', 11, struct binder_node_debug_info)
#define BINDER_GET_NODE_INFO_FOR_REF _IOWR('b', 12, struct binder_node_info_for_ref)
+#define BINDER_SET_CONTEXT_MGR_EXT _IOW('b', 13, struct flat_binder_object)

/*
* NOTE: Two special error codes you should check for when calling
@@ -276,6 +285,11 @@ struct binder_transaction_data {
} data;
};

+struct binder_transaction_data_secctx {
+ struct binder_transaction_data transaction_data;
+ binder_uintptr_t secctx;
+};
+
struct binder_transaction_data_sg {
struct binder_transaction_data transaction_data;
binder_size_t buffers_size;
@@ -311,6 +325,11 @@ enum binder_driver_return_protocol {
BR_OK = _IO('r', 1),
/* No parameters! */

+ BR_TRANSACTION_SEC_CTX = _IOR('r', 2,
+ struct binder_transaction_data_secctx),
+ /*
+ * binder_transaction_data_secctx: the received command.
+ */
BR_TRANSACTION = _IOR('r', 2, struct binder_transaction_data),
BR_REPLY = _IOR('r', 3, struct binder_transaction_data),
/*
--
2.20.1.97.g81188d93c3-goog
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