linux-hardening - [PATCH] xfs: replace deprecated strncpy with strscpy

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Message-ID: <20240405-strncpy-xfs-split1-v1-1-3e3df465adb9@google.com>
Date: Fri, 05 Apr 2024 19:52:27 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Chandan Babu R <chandan.babu@...cle.com>, "Darrick J. Wong" <djwong@...nel.org>
Cc: linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-hardening@...r.kernel.org, Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] xfs: replace deprecated strncpy with strscpy_pad

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

The current code has taken care of NUL-termination by memset()'ing
@label. This is followed by a strncpy() to perform the string copy.

Instead, use strscpy_pad() to get both 1) NUL-termination and 2)
NUL-padding which is needed as this is copied out to userspace.

Note that this patch uses the new 2-argument version of strscpy_pad
introduced in Commit e6584c3964f2f ("string: Allow 2-argument
strscpy()").

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.kernel.org

Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
Split from https://lore.kernel.org/all/20240401-strncpy-fs-xfs-xfs_ioctl-c-v1-1-02b9feb1989b@google.com/
with feedback from Christoph H.
---
 fs/xfs/xfs_ioctl.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index d0e2cec6210d..a1156a8b1e15 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1750,15 +1750,14 @@ xfs_ioc_getlabel(
 	char			__user *user_label)
 {
 	struct xfs_sb		*sbp = &mp->m_sb;
+	/* 1 larger than sb_fname, for a trailing NUL char */
 	char			label[XFSLABEL_MAX + 1];
 
 	/* Paranoia */
 	BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
 
-	/* 1 larger than sb_fname, so this ensures a trailing NUL char */
-	memset(label, 0, sizeof(label));
 	spin_lock(&mp->m_sb_lock);
-	strncpy(label, sbp->sb_fname, XFSLABEL_MAX);
+	strscpy_pad(label, sbp->sb_fname);
 	spin_unlock(&mp->m_sb_lock);
 
 	if (copy_to_user(user_label, label, sizeof(label)))

---
base-commit: c85af715cac0a951eea97393378e84bb49384734
change-id: 20240405-strncpy-xfs-split1-a2c408b934c6

Best regards,
--
Justin Stitt <justinstitt@...gle.com>