[PATCH] NFS: Prefer strscpy over strlcpy calls

[Azeem Shaikh <azeemshaikh38@gmail.com>]

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@gmail.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