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From:   Romain Perier <romain.perier@gmail.com>
To:     Kees Cook <keescook@chromium.org>,
        kernel-hardening@lists.openwall.com, Jessica Yu <jeyu@kernel.org>
Cc:     Romain Perier <romain.perier@gmail.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH 10/20] module: Manual replacement of the deprecated strlcpy() with return values
Date:   Mon, 22 Feb 2021 16:12:21 +0100
Message-Id: <20210222151231.22572-11-romain.perier@gmail.com>
In-Reply-To: <20210222151231.22572-1-romain.perier@gmail.com>
References: <20210222151231.22572-1-romain.perier@gmail.com>
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The strlcpy() reads the entire source buffer first, it is dangerous if
the source buffer lenght is unbounded or possibility non NULL-terminated.
It can lead to linear read overflows, crashes, etc...

As recommended in the deprecated interfaces [1], it should be replaced
by strscpy.

This commit replaces all calls to strlcpy that handle the return values
by the corresponding strscpy calls with new handling of the return
values (as it is quite different between the two functions).

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy

Signed-off-by: Romain Perier <romain.perier@gmail.com>
---
 kernel/module.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/module.c b/kernel/module.c
index 4bf30e4b3eaa..46aad8e92a81 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2814,6 +2814,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 	Elf_Sym *dst;
 	char *s;
 	Elf_Shdr *symsec = &info->sechdrs[info->index.sym];
+	ssize_t len;
 
 	/* Set up to point into init section. */
 	mod->kallsyms = mod->init_layout.base + info->mod_kallsyms_init_off;
@@ -2841,8 +2842,9 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 			    mod->kallsyms->typetab[i];
 			dst[ndst] = src[i];
 			dst[ndst++].st_name = s - mod->core_kallsyms.strtab;
-			s += strlcpy(s, &mod->kallsyms->strtab[src[i].st_name],
+			len = strscpy(s, &mod->kallsyms->strtab[src[i].st_name],
 				     KSYM_NAME_LEN) + 1;
+			s += (len != -E2BIG) ? len : 0;
 		}
 	}
 	mod->core_kallsyms.num_symtab = ndst;