linux-hardening - [PATCH][next] hpfs: Replace one-element array with flexible-array member

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Date:   Fri, 26 Mar 2021 12:35:10 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] hpfs: Replace one-element array with flexible-array
 member

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use “flexible array members”[1] for these cases. The older
style of one-element or zero-length arrays should no longer be used[2].

Also, this helps with the ongoing efforts to enable -Warray-bounds by
fixing the following warning:

  CC [M]  fs/hpfs/dir.o
fs/hpfs/dir.c: In function ‘hpfs_readdir’:
fs/hpfs/dir.c:163:41: warning: array subscript 1 is above array bounds of ‘u8[1]’ {aka ‘unsigned char[1]’} [-Warray-bounds]
  163 |         || de ->name[0] != 1 || de->name[1] != 1))
      |                                 ~~~~~~~~^~~

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 fs/hpfs/hpfs.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/hpfs/hpfs.h b/fs/hpfs/hpfs.h
index 302f45101a96..d92c4af3e1b4 100644
--- a/fs/hpfs/hpfs.h
+++ b/fs/hpfs/hpfs.h
@@ -356,7 +356,8 @@ struct hpfs_dirent {
   u8 no_of_acls;			/* number of ACL's (low 3 bits) */
   u8 ix;				/* code page index (of filename), see
 					   struct code_page_data */
-  u8 namelen, name[1];			/* file name */
+  u8 namelen;				/* file name length */
+  u8 name[];				/* file name */
   /* dnode_secno down;	  btree down pointer, if present,
      			  follows name on next word boundary, or maybe it
 			  precedes next dirent, which is on a word boundary. */
-- 
2.27.0