io_uring: Fix probe of disabled operations

BugLink: https://bugs.launchpad.net/bugs/2083196

[ Upstream commit 3e05b222382ec67dce7358d50b6006e91d028d8b ]

io_probe checks io_issue_def->not_supported, but we never really set
that field, as we mark non-supported functions through a specific ->prep
handler.  This means we end up returning IO_URING_OP_SUPPORTED, even for
disabled operations.  Fix it by just checking the prep handler itself.

Fixes: 66f4af93da ("io_uring: add support for probing opcodes")
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
Link: https://lore.kernel.org/r/20240619020620.5301-2-krisman@suse.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>

io_uring/opdef.c

@@ -721,6 +721,14 @@ const char *io_uring_get_opcode(u8 opcode)
 	return "INVALID";
 }
 
+bool io_uring_op_supported(u8 opcode)
+{
+	if (opcode < IORING_OP_LAST &&
+	    io_issue_defs[opcode].prep != io_eopnotsupp_prep)
+		return true;
+	return false;
+}
+
 void __init io_uring_optable_init(void)
 {
 	int i;

io_uring/opdef.h

@@ -17,8 +17,6 @@ struct io_issue_def {
 	unsigned		poll_exclusive : 1;
 	/* op supports buffer selection */
 	unsigned		buffer_select : 1;
-	/* opcode is not supported by this kernel */
-	unsigned		not_supported : 1;
 	/* skip auditing */
 	unsigned		audit_skip : 1;
 	/* supports ioprio */
@@ -50,5 +48,7 @@ struct io_cold_def {
 extern const struct io_issue_def io_issue_defs[];
 extern const struct io_cold_def io_cold_defs[];
 
+bool io_uring_op_supported(u8 opcode);
+
 void io_uring_optable_init(void);
 #endif

io_uring/register.c

@@ -112,7 +112,7 @@ static __cold int io_probe(struct io_ring_ctx *ctx, void __user *arg,
 
 	for (i = 0; i < nr_args; i++) {
 		p->ops[i].op = i;
-		if (!io_issue_defs[i].not_supported)
+		if (io_uring_op_supported(i))
 			p->ops[i].flags = IO_URING_OP_SUPPORTED;
 	}
 	p->ops_len = i;