We need to correct some aspects of the IORING_OP_FIXED_FD_INSTALL
command to take into account the security implications of making an
io_uring-private file descriptor generally accessible to a userspace
task.
The first change in this patch is to enable auditing of the FD_INSTALL
operation as installing a file descriptor into a task's file descriptor
table is a security relevant operation and something that admins/users
may want to audit.
The second change is to disable the io_uring credential override
functionality, also known as io_uring "personalities", in the
FD_INSTALL command. The credential override in FD_INSTALL is
particularly problematic as it affects the credentials used in the
security_file_receive() LSM hook. If a task were to request a
credential override via REQ_F_CREDS on a FD_INSTALL operation, the LSM
would incorrectly check to see if the overridden credentials of the
io_uring were able to "receive" the file as opposed to the task's
credentials. After discussions upstream, it's difficult to imagine a
use case where we would want to allow a credential override on a
FD_INSTALL operation so we are simply going to block REQ_F_CREDS on
IORING_OP_FIXED_FD_INSTALL operations.
Fixes: dc18b89ab113 ("io_uring/openclose: add support for IORING_OP_FIXED_FD_INSTALL")
Signed-off-by: Paul Moore <paul@xxxxxxxxxxxxxx>
---
io_uring/opdef.c | 1 -
io_uring/openclose.c | 4 ++++
2 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index 6705634e5f52..b1ee3a9c3807 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -471,7 +471,6 @@ const struct io_issue_def io_issue_defs[] = {
},
[IORING_OP_FIXED_FD_INSTALL] = {
.needs_file = 1,
- .audit_skip = 1,
.prep = io_install_fixed_fd_prep,
.issue = io_install_fixed_fd,
},
diff --git a/io_uring/openclose.c b/io_uring/openclose.c
index 0fe0dd305546..e3357dfa14ca 100644
--- a/io_uring/openclose.c
+++ b/io_uring/openclose.c
@@ -277,6 +277,10 @@ int io_install_fixed_fd_prep(struct io_kiocb *req, const struct io_uring_sqe *sq
if (flags & ~IORING_FIXED_FD_NO_CLOEXEC)
return -EINVAL;
+ /* ensure the task's creds are used when installing/receiving fds */
+ if (req->flags & REQ_F_CREDS)
+ return -EPERM;
+
/* default to O_CLOEXEC, disable if IORING_FIXED_FD_NO_CLOEXEC is set */
ifi = io_kiocb_to_cmd(req, struct io_fixed_install);
ifi->o_flags = O_CLOEXEC;
--
2.43.0
