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usb: gadget: f_fs: Fix Use-After-Free in AIO error path

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In ffs_epfile_write_iter() and ffs_epfile_read_iter(), when ffs_epfile_io()
fails with an error other than -EIOCBQUEUED, the io_data structure (`p`) is
freed. However, for AIO operations, the kiocb cancel function was already
armed and kiocb->private was set to `p`.

If a concurrent cancel operation (such as sys_io_cancel()) executes after
ffs_epfile_io() fails but before the function frees `p`, a Use-After-Free
can occur when the cancellation handler accesses the freed pointer.

To securely fix this race condition, we must properly un-arm the
cancellation. Invoking `kiocb->ki_complete()` does exactly this by
acquiring `ctx->ctx_lock` and safely removing the kiocb from the active
sequence. In doing so, it ensures that a parallel io_cancel can no longer
discover the kiocb, effectively closing the race window.

We then return -EIOCBQUEUED to notify the VFS layer that the kiocb has been
consumed and it should avoid attempting to complete the request again or
triggering subsequent completion handlers.

Fixes: de2080d41b ("gadget/function/f_fs.c: close leaks")
Cc: stable@vger.kernel.org
Reported-by: Xingyu Jin <xingyuj@google.com>
Assisted-by: Antigravity:gemini-3.1-pro
Signed-off-by: Neill Kapron <nkapron@google.com>
Link: https://patch.msgid.link/20260724235100.106011-1-nkapron@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Neill Kapron 2026-07-24 23:51:00 +00:00 committed by Greg Kroah-Hartman
parent 569dd7e5dc
commit e78dcb1f7e
1 changed files with 4 additions and 0 deletions
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4
drivers/usb/gadget/function/f_fs.c
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@ -1296,8 +1296,10 @@ static ssize_t ffs_epfile_write_iter(struct kiocb *kiocb, struct iov_iter *from)
if (res == -EIOCBQUEUED)
return res;
if (p->aio) {
kiocb->ki_complete(kiocb, res);
mmdrop(p->mm);
kfree(p);
return -EIOCBQUEUED;
} else {
*from = p->data;
}
@ -1345,9 +1347,11 @@ static ssize_t ffs_epfile_read_iter(struct kiocb *kiocb, struct iov_iter *to)
return res;
if (p->aio) {
kiocb->ki_complete(kiocb, res);
mmdrop(p->mm);
kfree(p->to_free);
kfree(p);
return -EIOCBQUEUED;
} else {
*to = p->data;
}