linux-hardening - [PATCH] NFS: Prefer strscpy over strlcpy calls

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Date:   Fri, 12 May 2023 15:57:49 +0000
From:   Azeem Shaikh <azeemshaikh38@...il.com>
To:     Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna@...nel.org>
Cc:     linux-hardening@...r.kernel.org,
        Azeem Shaikh <azeemshaikh38@...il.com>,
        linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] NFS: Prefer strscpy over strlcpy calls

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].
Check for strscpy()'s return value of -E2BIG on truncate for safe
replacement with strlcpy().

This is part of a tree-wide cleanup to remove the strlcpy() function
entirely from the kernel [2].

[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>
---
Note to reviewers: the one case where this patch would modify existing behavior
is when strlen(src)==destlen==0. Current behavior returns 0, with this patch it
would return -1.

Not sure what the implication of this updated behavior would be,
so bringing it to your attention.

 fs/nfs/nfsroot.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/nfsroot.c b/fs/nfs/nfsroot.c
index 620329b7e6ae..7600100ba26f 100644
--- a/fs/nfs/nfsroot.c
+++ b/fs/nfs/nfsroot.c
@@ -164,7 +164,7 @@ __setup("nfsroot=", nfs_root_setup);
 static int __init root_nfs_copy(char *dest, const char *src,
 				     const size_t destlen)
 {
-	if (strlcpy(dest, src, destlen) > destlen)
+	if (strscpy(dest, src, destlen) == -E2BIG)
 		return -1;
 	return 0;
 }
-- 
2.40.1.606.ga4b1b128d6-goog