From: Justin Stitt <justinstitt@google.com>
To: Chandan Babu R <chandan.babu@oracle.com>,
"Darrick J. Wong" <djwong@kernel.org>
Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org,
Justin Stitt <justinstitt@google.com>
Subject: [PATCH v2] xfs: xattr: replace strncpy and check for truncation
Date: Wed, 10 Apr 2024 20:14:12 +0000 [thread overview]
Message-ID: <20240410-strncpy-xattr-split2-v2-1-e6e03ebaeb65@google.com> (raw)
strncpy is deprecated and as such we should prefer less ambiguous and
more robust string interfaces [1].
There's a lot of manual memory management to get a prefix and name into
a string. Let's use an easier to understand and more robust interface in
scnprintf() to accomplish the same task while enabling us to check for
possible truncation, resulting in a soft warning.
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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- use "%.*s" format specifier
- use != instead of < to check for truncation (Christoph H.)
- Link to v1: https://lore.kernel.org/r/20240405-strncpy-xattr-split2-v1-1-90ab18232407@google.com
---
Tested with https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git
but using scripts + image from: https://github.com/tytso/xfstests-bld
test results: https://pastebin.com/44bjhpCp (no failures)
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_xattr.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/fs/xfs/xfs_xattr.c b/fs/xfs/xfs_xattr.c
index 364104e1b38a..54e7e7d24ce9 100644
--- a/fs/xfs/xfs_xattr.c
+++ b/fs/xfs/xfs_xattr.c
@@ -206,6 +206,7 @@ __xfs_xattr_put_listent(
{
char *offset;
int arraytop;
+ size_t combined_len, actual_len;
if (context->count < 0 || context->seen_enough)
return;
@@ -220,11 +221,16 @@ __xfs_xattr_put_listent(
return;
}
offset = context->buffer + context->count;
- memcpy(offset, prefix, prefix_len);
- offset += prefix_len;
- strncpy(offset, (char *)name, namelen); /* real name */
- offset += namelen;
- *offset = '\0';
+
+ combined_len = prefix_len + namelen;
+
+ /* plus one byte for \0 */
+ actual_len = scnprintf(offset, combined_len + 1, "%.*s%.*s",
+ prefix_len, prefix, namelen, name);
+
+ if (actual_len != combined_len)
+ xfs_warn(context->dp->i_mount,
+ "cannot completely copy context buffer resulting in truncation");
compute_size:
context->count += prefix_len + namelen + 1;
---
base-commit: c85af715cac0a951eea97393378e84bb49384734
change-id: 20240405-strncpy-xattr-split2-0a3aff0c6a20
Best regards,
--
Justin Stitt <justinstitt@google.com>
reply other threads:[~2024-04-10 20:14 UTC|newest]
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