[PATCH] exfat: keep FITRIM within the requested range

[Yang Wen]

exfat_find_free_bitmap() searches the entire allocation bitmap and may
wrap around to its beginning. exfat_trim_fs() does not verify that the
returned cluster is still within the requested FITRIM range.

As a result, a partial FITRIM operation may discard free clusters outside
the user-specified range and report a trimmed length larger than the
requested length.

Validate each returned cluster against the requested range and stop the
search when it wraps around or passes the range end.

Signed-off-by: Yang Wen <anmuxixixi@xxxxxxxxx>
---
 fs/exfat/balloc.c | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/fs/exfat/balloc.c b/fs/exfat/balloc.c
index e66ebf899778..c0ddd522c1e1 100644
--- a/fs/exfat/balloc.c
+++ b/fs/exfat/balloc.c
@@ -340,14 +340,27 @@ int exfat_trim_fs(struct inode *inode, struct fstrim_range *range)
 	mutex_lock(&sbi->bitmap_lock);
 
 	trim_begin = trim_end = exfat_find_free_bitmap(sb, clu_start);
-	if (trim_begin == EXFAT_EOF_CLUSTER)
+	/*
+	 * exfat_find_free_bitmap() may wrap around to the beginning of
+	 * the bitmap. Reject a cluster outside the requested range.
+	 */
+	if (trim_begin == EXFAT_EOF_CLUSTER ||
+		trim_begin < clu_start || trim_begin > clu_end)
 		goto unlock;
 
-	next_free_clu = exfat_find_free_bitmap(sb, trim_end + 1);
-	if (next_free_clu == EXFAT_EOF_CLUSTER)
-		goto unlock;
+	for (;;) {
+		if (trim_end >= clu_end)
+			break;
+
+		next_free_clu = exfat_find_free_bitmap(sb, trim_end + 1);
+		/*
+		 * Stop if the search wrapped around or moved beyond the requested
+		 * FITRIM range.
+		 */
+		if (next_free_clu == EXFAT_EOF_CLUSTER ||
+			next_free_clu <= trim_end || next_free_clu > clu_end)
+			break;
 
-	do {
 		if (next_free_clu == trim_end + 1) {
 			/* extend trim range for continuous free cluster */
 			trim_end++;
@@ -368,17 +381,11 @@ int exfat_trim_fs(struct inode *inode, struct fstrim_range *range)
 			trim_begin = trim_end = next_free_clu;
 		}
 
-		if (next_free_clu >= clu_end)
-			break;
-
 		if (fatal_signal_pending(current)) {
 			err = -ERESTARTSYS;
 			goto unlock;
 		}
-
-		next_free_clu = exfat_find_free_bitmap(sb, next_free_clu + 1);
-	} while (next_free_clu != EXFAT_EOF_CLUSTER &&
-			next_free_clu > trim_end);
+	}
 
 	/* try to trim remainder */
 	count = trim_end - trim_begin + 1;
-- 
2.34.1