Smack: Provide read control for io_uring_cmd

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
 };