[PATCH 2/2] ocfs2: fix readdir position truncation on 32-bit kernels

[Zhan Xusheng <zhanxusheng1024@gmail.com>]

In ocfs2_dir_foreach_blk_el(), the directory cookie position is
rebuilt with

	ctx->pos = (ctx->pos & ~(sb->s_blocksize - 1)) | offset;

`ctx->pos` is loff_t (signed 64-bit), while `sb->s_blocksize` is
unsigned long.  On 32-bit kernels unsigned long is 32-bit, so the mask

	~(sb->s_blocksize - 1)

is computed as a 32-bit unsigned value (e.g. 0xfffff000 for a 4 KiB
block size).  In the AND expression with the 64-bit `ctx->pos`, that
unsigned operand is zero-extended to 64 bits per the usual arithmetic
conversions, yielding 0x00000000fffff000.  The high 32 bits of
`ctx->pos` are silently cleared, even though directory size is
allowed to exceed 4 GiB.

When readdir() crosses the 4 GiB boundary on a 32-bit kernel the
position is reset back into the first 4 GiB block, making the
re-validation path re-enumerate already-returned dirents indefinitely.

This is ocfs2_dir_foreach_blk_el(), the extent-list readdir path taken
for all non-inline directories, so a directory large enough to cross
4 GiB reaches it.

This is the same class of bug that commit 3dce5bb82c97 ("exfat: Fix
bitwise operation having different size") fixed in exfat, and the
fix mirrors the equivalent ext4 fix in this series.  Cast the operand
to loff_t so the mask is 64-bit before the AND:

	ctx->pos = (ctx->pos & ~((loff_t)sb->s_blocksize - 1)) | offset;

64-bit kernels are unaffected.

Fixes: ccd979bdbce9 ("[PATCH] OCFS2: The Second Oracle Cluster Filesystem")
Cc: stable@vger.kernel.org
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
---
 fs/ocfs2/dir.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
index d7fc3cccf2f4..c30a86856d5b 100644
--- a/fs/ocfs2/dir.c
+++ b/fs/ocfs2/dir.c
@@ -1917,7 +1917,7 @@ static int ocfs2_dir_foreach_blk_el(struct inode *inode,
 				i += le16_to_cpu(de->rec_len);
 			}
 			offset = i;
-			ctx->pos = (ctx->pos & ~(sb->s_blocksize - 1))
+			ctx->pos = (ctx->pos & ~((loff_t)sb->s_blocksize - 1))
 				| offset;
 			*f_version = inode_query_iversion(inode);
 		}
-- 
2.43.0