forked from Minki/linux
4b836a1426
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@vger.kernel.org
Fixes:
|
||
|---|---|---|
| .. | ||
| binder_alloc_selftest.c | ||
| binder_alloc.c | ||
| binder_alloc.h | ||
| binder_internal.h | ||
| binder_trace.h | ||
| binder.c | ||
| binderfs.c | ||
| Kconfig | ||
| Makefile | ||