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Message-Id: <20230711222025.never.220-kees@kernel.org>
Date: Tue, 11 Jul 2023 15:20:28 -0700
From: Kees Cook <keescook@...omium.org>
To: Carlos Maiolino <cem@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
"Darrick J. Wong" <djwong@...nel.org>,
Dave Chinner <david@...morbit.com>,
Jeff Layton <jlayton@...nel.org>,
Eric Biggers <ebiggers@...nel.org>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
linux-xfs@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] libxfs: Redefine 1-element arrays as flexible arrays
To allow for code bases that include libxfs (e.g. the Linux kernel) and
build with strict flexible array handling (-fstrict-flex-arrays=3),
FORTIFY_SOURCE, and/or UBSAN bounds checking, redefine the remaining
1-element trailing arrays as true flexible arrays, but without changing
their structure sizes. This is done via a union to retain a single element
(named "legacy_padding"). As not all distro headers may yet have the
UAPI stddef.h __DECLARE_FLEX_ARRAY macro, include it explicitly in
platform_defs.h.in.
Addresses the warnings being seen under Linux:
https://lore.kernel.org/all/20230710170243.GF11456@frogsfrogsfrogs
Signed-off-by: Kees Cook <keescook@...omium.org>
---
include/platform_defs.h.in | 18 ++++++++++++++++++
libxfs/xfs_da_format.h | 38 ++++++++++++++++++++++++++++----------
libxfs/xfs_fs.h | 12 ++++++++++--
3 files changed, 56 insertions(+), 12 deletions(-)
diff --git a/include/platform_defs.h.in b/include/platform_defs.h.in
index 315ad77cfb78..a55965ce050d 100644
--- a/include/platform_defs.h.in
+++ b/include/platform_defs.h.in
@@ -134,6 +134,24 @@ static inline size_t __ab_c_size(size_t a, size_t b, size_t c)
# define fallthrough do {} while (0) /* fallthrough */
#endif
+#ifndef __DECLARE_FLEX_ARRAY
+/**
+ * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
+ *
+ * @type: The type of each flexible array element
+ * @name: The name of the flexible array member
+ *
+ * In order to have a flexible array member in a union or alone in a
+ * struct, it needs to be wrapped in an anonymous struct with at least 1
+ * named member, but that member can be empty.
+ */
+#define __DECLARE_FLEX_ARRAY(type, name) \
+ struct { \
+ struct { } __empty_ ## name; \
+ type name[]; \
+ }
+#endif
+
/* Only needed for the kernel. */
#define __init
diff --git a/libxfs/xfs_da_format.h b/libxfs/xfs_da_format.h
index 25e2841084e1..4af92f16d5cd 100644
--- a/libxfs/xfs_da_format.h
+++ b/libxfs/xfs_da_format.h
@@ -580,18 +580,23 @@ xfs_dir2_block_leaf_p(struct xfs_dir2_block_tail *btp)
/*
* Entries are packed toward the top as tight as possible.
*/
+struct xfs_attr_sf_entry {
+ uint8_t namelen; /* actual length of name (no NULL) */
+ uint8_t valuelen; /* actual length of value (no NULL) */
+ uint8_t flags; /* flags bits (see xfs_attr_leaf.h) */
+ uint8_t nameval[]; /* name & value bytes concatenated */
+};
+
struct xfs_attr_shortform {
struct xfs_attr_sf_hdr { /* constant-structure header block */
__be16 totsize; /* total bytes in shortform list */
__u8 count; /* count of active entries */
__u8 padding;
} hdr;
- struct xfs_attr_sf_entry {
- uint8_t namelen; /* actual length of name (no NULL) */
- uint8_t valuelen; /* actual length of value (no NULL) */
- uint8_t flags; /* flags bits (see xfs_attr_leaf.h) */
- uint8_t nameval[]; /* name & value bytes concatenated */
- } list[1]; /* variable sized array */
+ union {
+ struct xfs_attr_sf_entry legacy_padding;
+ __DECLARE_FLEX_ARRAY(struct xfs_attr_sf_entry, list);
+ };
};
typedef struct xfs_attr_leaf_map { /* RLE map of free bytes */
@@ -620,19 +625,29 @@ 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 */
+ union {
+ __u8 legacy_padding;
+ __DECLARE_FLEX_ARRAY(__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 */
+ union {
+ __u8 legacy_padding;
+ __DECLARE_FLEX_ARRAY(__u8, name); /* name bytes */
+ };
} xfs_attr_leaf_name_remote_t;
typedef struct xfs_attr_leafblock {
xfs_attr_leaf_hdr_t hdr; /* constant-structure header block */
- xfs_attr_leaf_entry_t entries[1]; /* sorted on key, not name */
+ union {
+ xfs_attr_leaf_entry_t legacy_padding;
+ /* sorted on key, not name */
+ __DECLARE_FLEX_ARRAY(xfs_attr_leaf_entry_t, entries);
+ };
/*
* The rest of the block contains the following structures after the
* leaf entries, growing from the bottom up. The variables are never
@@ -664,7 +679,10 @@ struct xfs_attr3_leaf_hdr {
struct xfs_attr3_leafblock {
struct xfs_attr3_leaf_hdr hdr;
- struct xfs_attr_leaf_entry entries[1];
+ union {
+ struct xfs_attr_leaf_entry legacy_padding;
+ __DECLARE_FLEX_ARRAY(struct xfs_attr_leaf_entry, entries);
+ };
/*
* The rest of the block contains the following structures after the
diff --git a/libxfs/xfs_fs.h b/libxfs/xfs_fs.h
index 1cfd5bc6520a..d6ec66ef0194 100644
--- a/libxfs/xfs_fs.h
+++ b/libxfs/xfs_fs.h
@@ -590,12 +590,20 @@ typedef struct xfs_attrlist_cursor {
struct xfs_attrlist {
__s32 al_count; /* number of entries in attrlist */
__s32 al_more; /* T/F: more attrs (do call again) */
- __s32 al_offset[1]; /* byte offsets of attrs [var-sized] */
+ union {
+ __s32 legacy_padding;
+ /* byte offsets of attrs [var-sized] */
+ __DECLARE_FLEX_ARRAY(__s32, al_offset);
+ };
};
struct xfs_attrlist_ent { /* data from attr_list() */
__u32 a_valuelen; /* number bytes in value of attr */
- char a_name[1]; /* attr name (NULL terminated) */
+ union {
+ char legacy_padding;
+ /* attr name (NULL terminated) */
+ __DECLARE_FLEX_ARRAY(char, a_name);
+ };
};
typedef struct xfs_fsop_attrlist_handlereq {
--
2.34.1
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