Merge tag 'scrub-fix-xattr-memory-mgmt-6.4_2023-04-11' of...

Merge tag 'scrub-fix-xattr-memory-mgmt-6.4_2023-04-11' of git://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into guilt/xfs-for-next

xfs: clean up memory management in xattr scrub [v24.5]

Currently, the extended attribute scrubber uses a single VLA to store
all the context information needed in various parts of the scrubber
code.  This includes xattr leaf block space usage bitmaps, and the value
buffer used to check the correctness of remote xattr value block
headers.  We try to minimize the insanity through the use of helper
functions, but this is a memory management nightmare.  Clean this up by
making the bitmap and value pointers explicit members of struct
xchk_xattr_buf.

Second, strengthen the xattr checking by teaching it to look for overlapping
data structures in the shortform attr data.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/scrub/attr.h

@@ -10,59 +10,15 @@
  * Temporary storage for online scrub and repair of extended attributes.
  */
 struct xchk_xattr_buf {
-	/* Size of @buf, in bytes. */
-	size_t			sz;
+	/* Bitmap of used space in xattr leaf blocks and shortform forks. */
+	unsigned long		*usedmap;
 
-	/*
-	 * Memory buffer -- either used for extracting attr values while
-	 * walking the attributes; or for computing attr block bitmaps when
-	 * checking the attribute tree.
-	 *
-	 * Each bitmap contains enough bits to track every byte in an attr
-	 * block (rounded up to the size of an unsigned long).  The attr block
-	 * used space bitmap starts at the beginning of the buffer; the free
-	 * space bitmap follows immediately after; and we have a third buffer
-	 * for storing intermediate bitmap results.
-	 */
-	uint8_t			buf[];
-};
-
-/* A place to store attribute values. */
-static inline uint8_t *
-xchk_xattr_valuebuf(
-	struct xfs_scrub	*sc)
-{
-	struct xchk_xattr_buf	*ab = sc->buf;
-
-	return ab->buf;
-}
-
-/* A bitmap of space usage computed by walking an attr leaf block. */
-static inline unsigned long *
-xchk_xattr_usedmap(
-	struct xfs_scrub	*sc)
-{
-	struct xchk_xattr_buf	*ab = sc->buf;
+	/* Bitmap of free space in xattr leaf blocks. */
+	unsigned long		*freemap;
 
-	return (unsigned long *)ab->buf;
-}
-
-/* A bitmap of free space computed by walking attr leaf block free info. */
-static inline unsigned long *
-xchk_xattr_freemap(
-	struct xfs_scrub	*sc)
-{
-	return xchk_xattr_usedmap(sc) +
-			BITS_TO_LONGS(sc->mp->m_attr_geo->blksize);
-}
-
-/* A bitmap used to hold temporary results. */
-static inline unsigned long *
-xchk_xattr_dstmap(
-	struct xfs_scrub	*sc)
-{
-	return xchk_xattr_freemap(sc) +
-			BITS_TO_LONGS(sc->mp->m_attr_geo->blksize);
-}
+	/* Memory buffer used to extract xattr values. */
+	void			*value;
+	size_t			value_sz;
+};
 
 #endif	/* __XFS_SCRUB_ATTR_H__ */

fs/xfs/scrub/scrub.c

@@ -189,7 +189,10 @@ xchk_teardown(
 	if (sc->flags & XCHK_REAPING_DISABLED)
 		xchk_start_reaping(sc);
 	if (sc->buf) {
+		if (sc->buf_cleanup)
+			sc->buf_cleanup(sc->buf);
 		kvfree(sc->buf);
+		sc->buf_cleanup = NULL;
 		sc->buf = NULL;
 	}
 

fs/xfs/scrub/scrub.h

@@ -77,7 +77,17 @@ struct xfs_scrub {
 	 */
 	struct xfs_inode		*ip;
 
+	/* Kernel memory buffer used by scrubbers; freed at teardown. */
 	void				*buf;
+
+	/*
+	 * Clean up resources owned by whatever is in the buffer.  Cleanup can
+	 * be deferred with this hook as a means for scrub functions to pass
+	 * data to repair functions.  This function must not free the buffer
+	 * itself.
+	 */
+	void				(*buf_cleanup)(void *buf);
+
 	uint				ilock_flags;
 
 	/* See the XCHK/XREP state flags below. */