[PATCH AUTOSEL 6.18-6.6] ntfs3: handle set_blocksize failures

[Sasha Levin]

From: Christoph Hellwig <hch@xxxxxx>

[ Upstream commit 24f7d1824b7581ae3daf9d443c5dfeabd89df6d8 ]

ntfs3 uses buffer_heads, which don't handle block size > PAGE_SIZE well.
Without this, mounting we will hit the

        BUG_ON(offset >= folio_size(folio));

in folio_set_bh on the first __bread_gfp call.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Link: https://patch.msgid.link/20260511071701.2456211-10-hch@xxxxxx
Signed-off-by: Christian Brauner (Amutable) <brauner@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---

LLM Generated explanations, may be completely bogus:

The background git searches finished and match the earlier analysis:

- **Related commits in 6.18.44:** `b3c151` (dummy `sb_min_blocksize`
  before boot read) and `28861e3` (moved blocksize init into
  `ntfs_init_from_boot`). Neither covers the unchecked
  `sb_set_blocksize()` calls this patch fixes.
- **This commit is not in the tree:** `git log --grep="handle
  set_blocksize"` returned nothing here, so the fix is still a candidate
  for backport.

The **YES** verdict stands: the vulnerable code is at
`fs/ntfs3/super.c:1137` and `:1188`, and the patch should apply cleanly.

 fs/ntfs3/super.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
index 9a2e3d0efd998..81fcc8c2114b6 100644
--- a/fs/ntfs3/super.c
+++ b/fs/ntfs3/super.c
@@ -1134,7 +1134,10 @@ static int ntfs_init_from_boot(struct super_block *sb, u32 sector_size,
 	rec->total = cpu_to_le32(sbi->record_size);
 	((struct ATTRIB *)Add2Ptr(rec, ao))->type = ATTR_END;
 
-	sb_set_blocksize(sb, min_t(u32, sbi->cluster_size, PAGE_SIZE));
+	if (!sb_set_blocksize(sb, min_t(u32, sbi->cluster_size, PAGE_SIZE))) {
+		err = -EINVAL;
+		goto out;
+	}
 
 	sbi->block_mask = sb->s_blocksize - 1;
 	sbi->blocks_per_cluster = sbi->cluster_size >> sb->s_blocksize_bits;
@@ -1185,7 +1188,8 @@ static int ntfs_init_from_boot(struct super_block *sb, u32 sector_size,
 			/*
 			 * Try alternative boot (last sector)
 			 */
-			sb_set_blocksize(sb, block_size);
+			if (!sb_set_blocksize(sb, block_size))
+				return -EINVAL;
 			hint = "Alternative boot";
 			dev_size = dev_size0; /* restore original size. */
 			goto read_boot;
-- 
2.53.0