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Subject[PATCH] binder: Address corner cases in deferred copy and fixup
Date
When handling BINDER_TYPE_FDA object we are pushing a parent fixup
with a certain skip_size but no scatter-gather copy object, since
the copy is handled standalone.
If BINDER_TYPE_FDA is the last children the scatter-gather copy
loop will never stop to skip it, thus we are left with an item in
the parent fixup list. This will trigger the BUG_ON().

Furthermore, it is possible to receive BINDER_TYPE_FDA object
with num_fds=0 which will confuse the scatter-gather code.

In the android userspace I could only find these usecases in the
libstagefright OMX implementation, so it might be that they're
doing something very weird, but nonetheless the kernel should not
panic about it.

Fixes: 09184ae9b575 ("binder: defer copies of pre-patched txn data")
Signed-off-by: Alessandro Astone <ales.astone@gmail.com>
---
drivers/android/binder.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 8351c5638880..18ad6825ba30 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -2295,7 +2295,7 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
{
int ret = 0;
struct binder_sg_copy *sgc, *tmpsgc;
- struct binder_ptr_fixup *pf =
+ struct binder_ptr_fixup *tmppf, *pf =
list_first_entry_or_null(pf_head, struct binder_ptr_fixup,
node);

@@ -2349,7 +2349,11 @@ static int binder_do_deferred_txn_copies(struct binder_alloc *alloc,
list_del(&sgc->node);
kfree(sgc);
}
- BUG_ON(!list_empty(pf_head));
+ list_for_each_entry_safe(pf, tmppf, pf_head, node) {
+ BUG_ON(pf->skip_size == 0);
+ list_del(&pf->node);
+ kfree(pf);
+ }
BUG_ON(!list_empty(sgc_head));

return ret > 0 ? -EINVAL : ret;
@@ -2486,6 +2490,9 @@ static int binder_translate_fd_array(struct list_head *pf_head,
struct binder_proc *proc = thread->proc;
int ret;

+ if (fda->num_fds == 0)
+ return 0;
+
fd_buf_size = sizeof(u32) * fda->num_fds;
if (fda->num_fds >= SIZE_MAX / sizeof(u32)) {
binder_user_error("%d:%d got transaction with invalid number of fds (%lld)\n",
--
2.35.1
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