Re: [PATCH] Smack: Provide read control for io_uring_cmd

[Kanchan Joshi <joshi.k@samsung.com>]

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On Tue, Aug 23, 2022 at 04:46:18PM -0700, Casey Schaufler wrote:
>Limit io_uring "cmd" options to files for which the caller has
>Smack read access. There may be cases where the cmd option may
>be closer to a write access than a read, but there is no way
>to make that determination.
>
>Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
>--
> security/smack/smack_lsm.c | 32 ++++++++++++++++++++++++++++++++
> 1 file changed, 32 insertions(+)
>
>diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>index 001831458fa2..bffccdc494cb 100644
>--- a/security/smack/smack_lsm.c
>+++ b/security/smack/smack_lsm.c
>@@ -42,6 +42,7 @@
> #include <linux/fs_context.h>
> #include <linux/fs_parser.h>
> #include <linux/watch_queue.h>
>+#include <linux/io_uring.h>
> #include "smack.h"
>
> #define TRANS_TRUE	"TRUE"
>@@ -4732,6 +4733,36 @@ static int smack_uring_sqpoll(void)
> 	return -EPERM;
> }
>
>+/**
>+ * smack_uring_cmd - check on file operations for io_uring
>+ * @ioucmd: the command in question
>+ *
>+ * Make a best guess about whether a io_uring "command" should
>+ * be allowed. Use the same logic used for determining if the
>+ * file could be opened for read in the absence of better criteria.
>+ */
>+static int smack_uring_cmd(struct io_uring_cmd *ioucmd)
>+{
>+	struct file *file = ioucmd->file;
>+	struct smk_audit_info ad;
>+	struct task_smack *tsp;
>+	struct inode *inode;
>+	int rc;
>+
>+	if (!file)
>+		return -EINVAL;
>+
>+	tsp = smack_cred(file->f_cred);
>+	inode = file_inode(file);
>+
>+	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_PATH);
>+	smk_ad_setfield_u_fs_path(&ad, file->f_path);
>+	rc = smk_tskacc(tsp, smk_of_inode(inode), MAY_READ, &ad);
>+	rc = smk_bu_credfile(file->f_cred, file, MAY_READ, rc);
>+
>+	return rc;
>+}
>+
> #endif /* CONFIG_IO_URING */
>
> struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = {
>@@ -4889,6 +4920,7 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
> #ifdef CONFIG_IO_URING
> 	LSM_HOOK_INIT(uring_override_creds, smack_uring_override_creds),
> 	LSM_HOOK_INIT(uring_sqpoll, smack_uring_sqpoll),
>+	LSM_HOOK_INIT(uring_cmd, smack_uring_cmd),
> #endif

Tried this on nvme device (/dev/ng0n1).
Took a while to come out of noob setup-related issues but I see that
smack is listed (in /sys/kernel/security/lsm), smackfs is present, and
the hook (smack_uring_cmd) gets triggered fine on doing I/O on
/dev/ng0n1.

I/O goes fine, which seems aligned with the label on /dev/ng0n1 (which
is set to floor).

$ chsmack -L /dev/ng0n1
/dev/ng0n1 access="_"

I ran fio (/usr/bin/fio), which also has the same label.
Hope you expect the same outcome.

Do you run something else to see that things are fine e.g. for
/dev/null, which also has the same label "_".
If yes, I can try the same on nvme side.

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