[PATCH v2] fs/qnx6: fix pointer arithmetic in directory iteration

[Arpith Kalaginanavoor <arpithk@nvidia.com>]

The conversion to qnx6_get_folio() in commit b2aa61556fcf
("qnx6: Convert qnx6_get_page() to qnx6_get_folio()")
introduced a regression in directory iteration. The pointer 'de'
and the 'limit' address were calculated using byte offsets from
a char pointer without scaling by the size of a QNX6 directory
entry.

This causes the driver to read from incorrect memory offsets,
leading to "invalid direntry size" errors and premature
termination of directory scans.

Fix this by casting 'kaddr' to 'struct qnx6_dir_entry *' before
applying the offset and last_entry(...) increments. This allows the
compiler to correctly scale the pointer arithmetic by the 32-byte
stride of the directory entry structure.

Fixes: b2aa61556fcf ("qnx6: Convert qnx6_get_page() to qnx6_get_folio()")
Cc: stable@vger.kernel.org
Signed-off-by: Arpith Kalaginanavoor <arpithk@nvidia.com>
---
v2: Use idiomatic pointer arithmetic: cast kaddr to struct
    qnx6_dir_entry * and add offset / last_entry() counts
    directly, rather than scaling a char * with
    QNX6_DIR_ENTRY_SIZE, as suggested by Al Viro.

 fs/qnx6/dir.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/qnx6/dir.c b/fs/qnx6/dir.c
index ae0c9846833d..8a26908f78c2 100644
--- a/fs/qnx6/dir.c
+++ b/fs/qnx6/dir.c
@@ -132,16 +132,16 @@ static int qnx6_readdir(struct file *file, struct dir_context *ctx)
 		struct qnx6_dir_entry *de;
 		struct folio *folio;
 		char *kaddr = qnx6_get_folio(inode, n, &folio);
-		char *limit;
+		struct qnx6_dir_entry *limit;
 
 		if (IS_ERR(kaddr)) {
 			pr_err("%s(): read failed\n", __func__);
 			ctx->pos = (n + 1) << PAGE_SHIFT;
 			return PTR_ERR(kaddr);
 		}
-		de = (struct qnx6_dir_entry *)(kaddr + offset);
-		limit = kaddr + last_entry(inode, n);
-		for (; (char *)de < limit; de++, ctx->pos += QNX6_DIR_ENTRY_SIZE) {
+		de = (struct qnx6_dir_entry *)kaddr + offset;
+		limit = (struct qnx6_dir_entry *)kaddr + last_entry(inode, n);
+		for (; de < limit; de++, ctx->pos += QNX6_DIR_ENTRY_SIZE) {
 			int size = de->de_size;
 			u32 no_inode = fs32_to_cpu(sbi, de->de_inode);
 
-- 
2.43.0