From patchwork Fri Feb 3 01:24:50 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. 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R. Silva" To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org Subject: [PATCH][next] xfs: Replace one-element arrays with flexible-array members Message-ID: MIME-Version: 1.0 Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org One-element arrays are deprecated, and we are replacing them with flexible array members instead. So, replace one-element arrays with flexible-array members in structures xfs_attr_leaf_name_local and xfs_attr_leaf_name_remote. The only binary differences reported after the changes are all like these: fs/xfs/libxfs/xfs_attr_leaf.o _@@ -435,7 +435,7 @@ 3b8: movzbl 0x2(%rbx),%eax 3bc: rol $0x8,%bp 3c0: movzwl %bp,%ebp - 3c3: lea 0x2(%rax,%rbp,1),%ebx + 3c3: lea 0x3(%rax,%rbp,1),%ebx 3c7: call 3cc 3c8: R_X86_64_PLT32 __tsan_func_exit-0x4 3cc: or $0x3,%ebx _@@ -454,7 +454,7 @@ 3ea: movzbl 0x8(%rbx),%ebx 3ee: call 3f3 3ef: R_X86_64_PLT32 __tsan_func_exit-0x4 - 3f3: add $0xa,%ebx + 3f3: add $0xb,%ebx 3f6: or $0x3,%ebx 3f9: add $0x1,%ebx 3fc: mov %ebx,%eax similar changes in fs/xfs/scrub/attr.o and fs/xfs/xfs.o object files. And the reason for this is because of the round_up() macro called in functions xfs_attr_leaf_entsize_remote() and xfs_attr_leaf_entsize_local(), which is compensanting for the one-byte reduction in size (due to the flex-array transformation) of structures xfs_attr_leaf_name_remote and xfs_attr_leaf_name_local. So, sizes remain the same before and after changes. This helps with the ongoing efforts to tighten the FORTIFY_SOURCE routines on memcpy() and help us make progress towards globally enabling -fstrict-flex-arrays=3 [1]. Link: https://github.com/KSPP/linux/issues/79 Link: https://github.com/KSPP/linux/issues/251 Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1] Signed-off-by: Gustavo A. R. Silva Reviewed-by: Kees Cook --- fs/xfs/libxfs/xfs_da_format.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/xfs/libxfs/xfs_da_format.h b/fs/xfs/libxfs/xfs_da_format.h index 25e2841084e1..e1e62ebb0c44 100644 --- a/fs/xfs/libxfs/xfs_da_format.h +++ b/fs/xfs/libxfs/xfs_da_format.h @@ -620,14 +620,14 @@ typedef struct xfs_attr_leaf_entry { /* sorted on key, not name */ typedef struct xfs_attr_leaf_name_local { __be16 valuelen; /* number of bytes in value */ __u8 namelen; /* length of name bytes */ - __u8 nameval[1]; /* name/value bytes */ + __u8 nameval[]; /* name/value bytes */ } xfs_attr_leaf_name_local_t; typedef struct xfs_attr_leaf_name_remote { __be32 valueblk; /* block number of value bytes */ __be32 valuelen; /* number of bytes in value */ __u8 namelen; /* length of name bytes */ - __u8 name[1]; /* name bytes */ + __u8 name[]; /* name bytes */ } xfs_attr_leaf_name_remote_t; typedef struct xfs_attr_leafblock { @@ -747,13 +747,13 @@ xfs_attr3_leaf_name_local(xfs_attr_leafblock_t *leafp, int idx) */ static inline int xfs_attr_leaf_entsize_remote(int nlen) { - return round_up(sizeof(struct xfs_attr_leaf_name_remote) - 1 + + return round_up(sizeof(struct xfs_attr_leaf_name_remote) + nlen, XFS_ATTR_LEAF_NAME_ALIGN); } static inline int xfs_attr_leaf_entsize_local(int nlen, int vlen) { - return round_up(sizeof(struct xfs_attr_leaf_name_local) - 1 + + return round_up(sizeof(struct xfs_attr_leaf_name_local) + nlen + vlen, XFS_ATTR_LEAF_NAME_ALIGN); }