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osmo_io_uring: Cancel pending request, free msghdr on completion 

There is always a completion after cancelling a uring request.

Because uring requests use msghdr pointer as user data, we cannot just
free the msghdr after cancelling. Upon completion (received after
cancelling), the user data still points to the msghdr. To prevent a
use-after-free bug, msghdr is not freed, but detached from iofd
instance. Then upon completion, the msghdr (if it was detached from
iofd) is freed.

Related: OS#5751
Change-Id: Ic253f085dd6362db85f029f46350951472210a02
This commit is contained in:
Andreas Eversberg 2024-02-15 10:16:33 +01:00
parent 80c05877d8
commit 1a531e264f
1 changed files with 18 additions and 2 deletions
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20
src/core/osmo_io_uring.c
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@ -252,6 +252,11 @@ static void iofd_uring_cqe(struct io_uring *ring)
io_uring_cqe_seen(ring, cqe);
continue;
}
if (!msghdr->iofd) {
io_uring_cqe_seen(ring, cqe);
iofd_msghdr_free(msghdr);
continue;
}
rc = cqe->res;
/* Hand the entry back to the kernel before */
@ -307,20 +312,31 @@ static int iofd_uring_register(struct osmo_io_fd *iofd)
static int iofd_uring_unregister(struct osmo_io_fd *iofd)
{
struct io_uring_sqe *sqe;
struct iofd_msghdr *msghdr;
if (iofd->u.uring.read_msghdr) {
msghdr = iofd->u.uring.read_msghdr;
sqe = io_uring_get_sqe(&g_ring.ring);
OSMO_ASSERT(sqe != NULL);
io_uring_sqe_set_data(sqe, NULL);
LOGPIO(iofd, LOGL_DEBUG, "Cancelling read\n");
io_uring_prep_cancel(sqe, iofd->u.uring.read_msghdr, 0);
iofd->u.uring.read_msghdr = NULL;
talloc_steal(OTC_GLOBAL, msghdr);
msghdr->iofd = NULL;
io_uring_prep_cancel(sqe, msghdr, 0);
}
if (iofd->u.uring.write_msghdr) {
msghdr = iofd->u.uring.write_msghdr;
sqe = io_uring_get_sqe(&g_ring.ring);
OSMO_ASSERT(sqe != NULL);
io_uring_sqe_set_data(sqe, NULL);
LOGPIO(iofd, LOGL_DEBUG, "Cancelling write\n");
io_uring_prep_cancel(sqe, iofd->u.uring.write_msghdr, 0);
iofd->u.uring.write_msghdr = NULL;
talloc_steal(OTC_GLOBAL, msghdr);
msgb_free(msghdr->msg);
msghdr->iofd = NULL;
io_uring_prep_cancel(sqe, msghdr, 0);
}
io_uring_submit(&g_ring.ring);