linux-hardening - [PATCH] um: Remove strlcpy declaration

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Date:   Mon,  3 Jul 2023 16:06:41 +0000
From:   Azeem Shaikh <azeemshaikh38@...il.com>
To:     Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>
Cc:     linux-hardening@...r.kernel.org,
        Azeem Shaikh <azeemshaikh38@...il.com>,
        linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Kees Cook <keescook@...omium.org>,
        Haowen Bai <baihaowen@...zu.com>
Subject: [PATCH] um: Remove strlcpy declaration

strlcpy() reads the entire source buffer first.
This read may exceed the destination size limit.
This is both inefficient and can lead to linear read
overflows if a source string is not NUL-terminated [1].
In an effort to remove strlcpy() completely [2], replace
strlcpy() here with strscpy().
No return values were used, so direct replacement is safe.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
[2] https://github.com/KSPP/linux/issues/89

Signed-off-by: Azeem Shaikh <azeemshaikh38@...il.com>
---
 arch/um/include/shared/user.h |    1 -
 arch/um/os-Linux/umid.c       |    6 +++---
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
index 0347a190429c..981e11d8e025 100644
--- a/arch/um/include/shared/user.h
+++ b/arch/um/include/shared/user.h
@@ -50,7 +50,6 @@ static inline int printk(const char *fmt, ...)
 #endif
 
 extern int in_aton(char *str);
-extern size_t strlcpy(char *, const char *, size_t);
 extern size_t strlcat(char *, const char *, size_t);
 extern size_t strscpy(char *, const char *, size_t);
 
diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
index 7a1abb829930..288c422bfa96 100644
--- a/arch/um/os-Linux/umid.c
+++ b/arch/um/os-Linux/umid.c
@@ -40,7 +40,7 @@ static int __init make_uml_dir(void)
 				__func__);
 			goto err;
 		}
-		strlcpy(dir, home, sizeof(dir));
+		strscpy(dir, home, sizeof(dir));
 		uml_dir++;
 	}
 	strlcat(dir, uml_dir, sizeof(dir));
@@ -243,7 +243,7 @@ int __init set_umid(char *name)
 	if (strlen(name) > UMID_LEN - 1)
 		return -E2BIG;
 
-	strlcpy(umid, name, sizeof(umid));
+	strscpy(umid, name, sizeof(umid));
 
 	return 0;
 }
@@ -262,7 +262,7 @@ static int __init make_umid(void)
 	make_uml_dir();
 
 	if (*umid == '\0') {
-		strlcpy(tmp, uml_dir, sizeof(tmp));
+		strscpy(tmp, uml_dir, sizeof(tmp));
 		strlcat(tmp, "XXXXXX", sizeof(tmp));
 		fd = mkstemp(tmp);
 		if (fd < 0) {
-- 
2.41.0.255.g8b1d071c50-goog