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binder: create node flag to request sender's security context
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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>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Todd Kjos authored and Greg Kroah-Hartman committed Jan 22, 2019
1 parent 8fdf906 commit ec74136
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Showing 2 changed files with 102 additions and 23 deletions.
106 changes: 83 additions & 23 deletions drivers/android/binder.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)
*
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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
*
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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,
Expand All @@ -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;
Expand Down Expand Up @@ -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:
Expand Down Expand Up @@ -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))
Expand Down Expand Up @@ -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))
Expand All @@ -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);
Expand Down Expand Up @@ -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 *));

tr.secctx = t->security_ctx;
if (t->security_ctx) {
cmd = BR_TRANSACTION_SEC_CTX;
trsize = sizeof(tr);
}
if (put_user(cmd, (uint32_t __user *)ptr)) {
if (t_from)
binder_thread_dec_tmpref(t_from);
Expand All @@ -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);

Expand All @@ -4325,24 +4370,26 @@ 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);
binder_debug(BINDER_DEBUG_TRANSACTION,
"%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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down
19 changes: 19 additions & 0 deletions include/uapi/linux/android/binder.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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),
/*
Expand Down

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