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d5e5cd3654
dummy_hcd embeds a single shared usb_request (dum->fifo_req) that the
"emulated single-request FIFO" fast-path in dummy_queue() reuses for
small IN transfers: it copies the caller's request into it
(req->req = *_req) and queues it, treating list_empty(&fifo_req.queue)
as "the slot is free".
The completion side (dummy_timer/transfer/nuke/dummy_dequeue) follows
the standard pattern: list_del_init(&req->queue) unlinks the request,
then the lock is dropped and usb_gadget_giveback_request() invokes
req->complete(). But list_del_init() makes fifo_req.queue look empty
*before* the completion callback returns, so a concurrent dummy_queue()
on another CPU sees the slot as free, reuses fifo_req and runs
req->req = *_req -- overwriting req->complete while dummy_timer is
mid-calling it. The indirect call then jumps to a clobbered pointer,
causing a general protection fault / page fault in dummy_timer
(syzkaller extid faf3a6cf579fc65591ca). The clobbering write is an
in-bounds memcpy on a live shared object, so KASAN cannot flag it.
Add a fifo_req_busy bit covering the shared request's whole lifetime:
set it in dummy_queue() when the FIFO fast-path takes fifo_req (making
it the fast-path guard, replacing the list_empty(&fifo_req.queue)
test), and clear it after the completion callback has returned, via a
dummy_giveback() helper used at all four gadget-request giveback
sites. The shared slot can no longer be reused until its completion
callback has finished.
Reported-by: syzbot+faf3a6cf579fc65591ca@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=faf3a6cf579fc65591ca
Fixes:
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|---|---|---|
| .. | ||
| function | ||
| legacy | ||
| udc | ||
| composite.c | ||
| config.c | ||
| configfs.c | ||
| configfs.h | ||
| epautoconf.c | ||
| functions.c | ||
| Kconfig | ||
| Makefile | ||
| u_f.c | ||
| u_os_desc.h | ||
| usbstring.c | ||