[PATCH 6.18 176/396] tracing/probes: Reject $arg0 in meta argument expansion

6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Raushan Patel <[email protected]>

commit 00a8ce2a2a9fa17674e1feec4d9105c1a5d6a419 upstream.

traceprobe_expand_meta_args() parses $argN with simple_strtoul() and
calls sprint_nth_btf_arg(n - 1, ...). For $arg0, n is 0 so the index is
-1. Because ctx->nr_params is signed, the "idx >= nr_params" guard in
sprint_nth_btf_arg() does not catch the negative index, and
ctx->params[-1].name_off is read out of bounds.

The normal per-argument path (parse_probe_vars()) already rejects
$arg0 via its argument-number check, but meta-argument expansion runs
before per-argument parsing and substitutes the value first, bypassing
that check.

Reject $arg0 explicitly during expansion.

Link: https://lore.kernel.org/all/[email protected]/

Fixes: 18b1e870a496 ("tracing/probes: Add $arg* meta argument for all function args")
Cc: [email protected]
Signed-off-by: Raushan Patel <[email protected]>
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 kernel/trace/trace_probe.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -1906,7 +1906,11 @@ const char **traceprobe_expand_meta_args
 				trace_probe_log_err(0, BAD_VAR);
 				return ERR_PTR(-ENOENT);
 			}
-			/* Note: $argN starts from $arg1 */
+			/* Note: $argN starts from $arg1, so $arg0 is invalid. */
+			if (n == 0) {
+				trace_probe_log_err(0, BAD_ARG_NUM);
+				return ERR_PTR(-EINVAL);
+			}
 			ret = sprint_nth_btf_arg(n - 1, type, buf + used,
 						 bufsize - used, ctx);
 			if (ret < 0)