[PATCH] fs/ntfs3: resize log->one_page_buf when adopting on-disk page size

[Jamie Nguyen <jamien@nvidia.com>]

log_replay() allocates log->one_page_buf using the page size that was
chosen from the host PAGE_SIZE:

	log->one_page_buf = kmalloc(log->page_size, GFP_NOFS);

Later, when a restart area is found, the log page size recorded on disk
is adopted:

	t32 = le32_to_cpu(log->rst_info.r_page->sys_page_size);
	if (log->page_size != t32) {
		log->l_size = log->orig_file_size;
		log->page_size = norm_file_page(t32, &log->l_size,
						t32 == DefaultLogPageSize);
	}

If the on-disk page size is larger than the size used for the initial
allocation, log->page_size grows but one_page_buf is left at its
original, smaller size. A subsequent unaligned read_log_page() then
reads log->page_size bytes into the undersized scratch buffer:

	page_buf = page_off ? log->one_page_buf : *buffer;
	err = ntfs_read_run_nb_ra(ni->mi.sbi, &ni->file.run, page_vbo, page_buf,
				  log->page_size, NULL, &log->read_ahead);

overflowing the allocation. This is reachable when mounting a dirty
NTFS volume whose log was formatted with a page size larger than the
buffer initially allocated on the mounting host (for example a 64K-log
volume mounted on a host that allocated a 4K scratch buffer).

Grow one_page_buf when the adopted on-disk page size exceeds the size
used for the initial allocation. On krealloc() failure the original
buffer is left intact and freed by the existing error path.

Fixes: b46acd6a6a627 ("fs/ntfs3: Add NTFS journal")
Reported-by: Carol L Soto <csoto@nvidia.com>
Signed-off-by: Jamie Nguyen <jamien@nvidia.com>
---
 fs/ntfs3/fslog.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/fs/ntfs3/fslog.c b/fs/ntfs3/fslog.c
index 95e1cdb47..b44bcfd31 100644
--- a/fs/ntfs3/fslog.c
+++ b/fs/ntfs3/fslog.c
@@ -3976,9 +3976,28 @@ int log_replay(struct ntfs_inode *ni, bool *initialized)
 	 */
 	t32 = le32_to_cpu(log->rst_info.r_page->sys_page_size);
 	if (log->page_size != t32) {
+		u32 old_page_size = log->page_size;
+
 		log->l_size = log->orig_file_size;
 		log->page_size = norm_file_page(t32, &log->l_size,
 						t32 == DefaultLogPageSize);
+
+		/*
+		 * If the adopted on-disk page size is larger than the size used
+		 * to allocate one_page_buf above, grow the scratch buffer so a
+		 * later read_log_page() cannot overflow it.
+		 */
+		if (log->page_size > old_page_size) {
+			void *buf;
+
+			buf = krealloc(log->one_page_buf, log->page_size,
+				       GFP_NOFS);
+			if (!buf) {
+				err = -ENOMEM;
+				goto out;
+			}
+			log->one_page_buf = buf;
+		}
 	}
 
 	if (log->page_size != t32 ||
-- 
2.43.0