From 16bae3e1377846734ec6b87eee459c0f3551692c Mon Sep 17 00:00:00 2001 From: Paul Moore Date: Tue, 23 Jan 2024 16:55:02 -0500 Subject: [PATCH] io_uring: enable audit and restrict cred override for IORING_OP_FIXED_FD_INSTALL 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 Link: https://lore.kernel.org/r/20240123215501.289566-2-paul@paul-moore.com Signed-off-by: Jens Axboe --- 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;