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Date: Thu, 20 Aug 2020 11:20:44 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Todd Kjos <tkjos@...gle.com>,
Jann Horn <jannh@...gle.com>, Martijn Coenen <maco@...roid.com>
Subject: [PATCH 4.9 071/212] binder: Prevent context manager from incrementing ref 0
From: Jann Horn <jannh@...gle.com>
commit 4b836a1426cb0f1ef2a6e211d7e553221594f8fc upstream.
Binder is designed such that a binder_proc never has references to
itself. If this rule is violated, memory corruption can occur when a
process sends a transaction to itself; see e.g.
<https://syzkaller.appspot.com/bug?extid=09e05aba06723a94d43d>.
There is a remaining edgecase through which such a transaction-to-self
can still occur from the context of a task with BINDER_SET_CONTEXT_MGR
access:
- task A opens /dev/binder twice, creating binder_proc instances P1
and P2
- P1 becomes context manager
- P2 calls ACQUIRE on the magic handle 0, allocating index 0 in its
handle table
- P1 dies (by closing the /dev/binder fd and waiting a bit)
- P2 becomes context manager
- P2 calls ACQUIRE on the magic handle 0, allocating index 1 in its
handle table
[this triggers a warning: "binder: 1974:1974 tried to acquire
reference to desc 0, got 1 instead"]
- task B opens /dev/binder once, creating binder_proc instance P3
- P3 calls P2 (via magic handle 0) with (void*)1 as argument (two-way
transaction)
- P2 receives the handle and uses it to call P3 (two-way transaction)
- P3 calls P2 (via magic handle 0) (two-way transaction)
- P2 calls P2 (via handle 1) (two-way transaction)
And then, if P2 does *NOT* accept the incoming transaction work, but
instead closes the binder fd, we get a crash.
Solve it by preventing the context manager from using ACQUIRE on ref 0.
There shouldn't be any legitimate reason for the context manager to do
that.
Additionally, print a warning if someone manages to find another way to
trigger a transaction-to-self bug in the future.
Cc: stable@...r.kernel.org
Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
Acked-by: Todd Kjos <tkjos@...gle.com>
Signed-off-by: Jann Horn <jannh@...gle.com>
Reviewed-by: Martijn Coenen <maco@...roid.com>
Link: https://lore.kernel.org/r/20200727120424.1627555-1-jannh@google.com
[manual backport: remove fine-grained locking and error reporting that
don't exist in <=4.9]
Signed-off-by: Jann Horn <jannh@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
drivers/android/binder.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -1427,6 +1427,10 @@ static void binder_transaction(struct bi
return_error = BR_DEAD_REPLY;
goto err_dead_binder;
}
+ if (WARN_ON(proc == target_proc)) {
+ return_error = BR_FAILED_REPLY;
+ goto err_invalid_target_handle;
+ }
if (security_binder_transaction(proc->tsk,
target_proc->tsk) < 0) {
return_error = BR_FAILED_REPLY;
@@ -1830,6 +1834,11 @@ static int binder_thread_write(struct bi
ptr += sizeof(uint32_t);
if (target == 0 && binder_context_mgr_node &&
(cmd == BC_INCREFS || cmd == BC_ACQUIRE)) {
+ if (binder_context_mgr_node->proc == proc) {
+ binder_user_error("%d:%d context manager tried to acquire desc 0\n",
+ proc->pid, thread->pid);
+ return -EINVAL;
+ }
ref = binder_get_ref_for_node(proc,
binder_context_mgr_node);
if (ref->desc != target) {
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