linux-kernel - [PATCH] modpost: fix removing numeric suffixes

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Message-Id: <20220524152718.331773-1-alexandr.lobakin@intel.com>
Date:   Tue, 24 May 2022 17:27:18 +0200
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Michal Nazarewicz <mina86@...a86.com>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] modpost: fix removing numeric suffixes

With the `-z unique-symbol` linker flag or any similar mechanism,
it is possible to trigger the following:

ERROR: modpost: "param_set_uint.0" [vmlinux] is a static EXPORT_SYMBOL

The reason is that for now the condition from remove_dot():

if (m && (s[n + m] == '.' || s[n + m] == 0))

which was designed to test if it's a dot or a '\0' after the suffix
is never satisfied.
This is due to that `s[n + m]` always points to the last digit of a
numeric suffix, not on the symbol next to it (from a custom debug
print added to modpost):

param_set_uint.0, s[n + m] is '0', s[n + m + 1] is '\0'

So it's off-by-one and was like that since 2014.

Fix this for the sake of any potential upcoming features, but don't
bother stable-backporting, as it's well hidden -- apart from that
LD flag, it can be triggered only with GCC LTO which never landed
upstream.

Fixes: fcd38ed0ff26 ("scripts: modpost: fix compilation warning")
Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
---
 scripts/mod/modpost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 6f5c605ab0fb..fd04ba057490 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1905,7 +1905,7 @@ static char *remove_dot(char *s)

 	if (n && s[n]) {
 		size_t m = strspn(s + n + 1, "0123456789");
-		if (m && (s[n + m] == '.' || s[n + m] == 0))
+		if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0))
 			s[n] = 0;
 	}
 	return s;
-- 
2.36.1