[PATCH] xfs: Replace strncpy() with strscpy_pad() in tracepoint error paths

[Kees Cook <kees@kernel.org>]

Replace the deprecated[1] strncpy() with strscpy_pad() in the
xfile_create and xmbuf_create tracepoints.

Both tracepoints use file_path() to resolve a pathname into
__entry->pathname (a char[MAXNAMELEN] trace ring buffer field). On
failure, the error path overwrites the buffer with the string literal
"(unknown)" via strncpy(). The original strncpy() zero-pads the
remaining 246 bytes (MAXNAMELEN is 256, "(unknown)" is 10 bytes
including NUL).

strscpy_pad() preserves this zero-padding, which matters because the
destination is a trace ring buffer entry: ring buffer slots are not
zeroed on allocation, and the raw buffer is readable by userspace via
tracefs. The zero-padding ensures no stale data remains in the
buffer after the error path overwrites it.

The source is a 10-byte string literal into a 256-byte destination,
so there is no behavioral change.

Link: https://github.com/KSPP/linux/issues/90 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
---
 fs/xfs/scrub/trace.h | 3 +--
 fs/xfs/xfs_trace.h   | 3 +--
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index 39ea651cbb75..46c420f51129 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -980,8 +980,7 @@ TRACE_EVENT(xfile_create,
 		__entry->ino = file_inode(xf->file)->i_ino;
 		path = file_path(xf->file, __entry->pathname, MAXNAMELEN);
 		if (IS_ERR(path))
-			strncpy(__entry->pathname, "(unknown)",
-					sizeof(__entry->pathname));
+			strscpy_pad(__entry->pathname, "(unknown)");
 	),
 	TP_printk("xfino 0x%lx path '%s'",
 		  __entry->ino,
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 813e5a9f57eb..9f9fb86097ed 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -5101,8 +5101,7 @@ TRACE_EVENT(xmbuf_create,
 		__entry->ino = file_inode(file)->i_ino;
 		path = file_path(file, __entry->pathname, MAXNAMELEN);
 		if (IS_ERR(path))
-			strncpy(__entry->pathname, "(unknown)",
-					sizeof(__entry->pathname));
+			strscpy_pad(__entry->pathname, "(unknown)");
 	),
 	TP_printk("dev %d:%d xmino 0x%lx path '%s'",
 		  MAJOR(__entry->dev), MINOR(__entry->dev),
-- 
2.34.1