5.10-stable review patch. If anyone has any objections, please let me know.
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From: Gustavo A. R. Silva gustavoars@kernel.org
[ Upstream commit c0a744dcaa29e9537e8607ae9c965ad936124a4d ]
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].
Use an anonymous union with a couple of anonymous structs in order to keep userspace unchanged:
$ pahole -C nfs_fhbase_new fs/nfsd/nfsfh.o struct nfs_fhbase_new { union { struct { __u8 fb_version_aux; /* 0 1 */ __u8 fb_auth_type_aux; /* 1 1 */ __u8 fb_fsid_type_aux; /* 2 1 */ __u8 fb_fileid_type_aux; /* 3 1 */ __u32 fb_auth[1]; /* 4 4 */ }; /* 0 8 */ struct { __u8 fb_version; /* 0 1 */ __u8 fb_auth_type; /* 1 1 */ __u8 fb_fsid_type; /* 2 1 */ __u8 fb_fileid_type; /* 3 1 */ __u32 fb_auth_flex[0]; /* 4 0 */ }; /* 0 4 */ }; /* 0 8 */
/* size: 8, cachelines: 1, members: 1 */ /* last cacheline: 8 bytes */ };
Also, this helps with the ongoing efforts to enable -Warray-bounds by fixing the following warnings:
fs/nfsd/nfsfh.c: In function ‘nfsd_set_fh_dentry’: fs/nfsd/nfsfh.c:191:41: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds] 191 | ntohl((__force __be32)fh->fh_fsid[1]))); | ~~~~~~~~~~~^~~ ./include/linux/kdev_t.h:12:46: note: in definition of macro ‘MKDEV’ 12 | #define MKDEV(ma,mi) (((ma) << MINORBITS) | (mi)) | ^~ ./include/uapi/linux/byteorder/little_endian.h:40:26: note: in expansion of macro ‘__swab32’ 40 | #define __be32_to_cpu(x) __swab32((__force __u32)(__be32)(x)) | ^~~~~~~~ ./include/linux/byteorder/generic.h:136:21: note: in expansion of macro ‘__be32_to_cpu’ 136 | #define ___ntohl(x) __be32_to_cpu(x) | ^~~~~~~~~~~~~ ./include/linux/byteorder/generic.h:140:18: note: in expansion of macro ‘___ntohl’ 140 | #define ntohl(x) ___ntohl(x) | ^~~~~~~~ fs/nfsd/nfsfh.c:191:8: note: in expansion of macro ‘ntohl’ 191 | ntohl((__force __be32)fh->fh_fsid[1]))); | ^~~~~ fs/nfsd/nfsfh.c:192:32: warning: array subscript 2 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds] 192 | fh->fh_fsid[1] = fh->fh_fsid[2]; | ~~~~~~~~~~~^~~ fs/nfsd/nfsfh.c:192:15: warning: array subscript 1 is above array bounds of ‘__u32[1]’ {aka ‘unsigned int[1]’} [-Warray-bounds] 192 | fh->fh_fsid[1] = fh->fh_fsid[2]; | ~~~~~~~~~~~^~~
[1] https://en.wikipedia.org/wiki/Flexible_array_member [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-an...
Link: https://github.com/KSPP/linux/issues/79 Link: https://github.com/KSPP/linux/issues/109 Signed-off-by: Gustavo A. R. Silva gustavoars@kernel.org Signed-off-by: Chuck Lever chuck.lever@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- include/uapi/linux/nfsd/nfsfh.h | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/include/uapi/linux/nfsd/nfsfh.h b/include/uapi/linux/nfsd/nfsfh.h index ff0ca88b1c8f6..427294dd56a1b 100644 --- a/include/uapi/linux/nfsd/nfsfh.h +++ b/include/uapi/linux/nfsd/nfsfh.h @@ -64,13 +64,24 @@ struct nfs_fhbase_old { * in include/linux/exportfs.h for currently registered values. */ struct nfs_fhbase_new { - __u8 fb_version; /* == 1, even => nfs_fhbase_old */ - __u8 fb_auth_type; - __u8 fb_fsid_type; - __u8 fb_fileid_type; - __u32 fb_auth[1]; -/* __u32 fb_fsid[0]; floating */ -/* __u32 fb_fileid[0]; floating */ + union { + struct { + __u8 fb_version_aux; /* == 1, even => nfs_fhbase_old */ + __u8 fb_auth_type_aux; + __u8 fb_fsid_type_aux; + __u8 fb_fileid_type_aux; + __u32 fb_auth[1]; + /* __u32 fb_fsid[0]; floating */ + /* __u32 fb_fileid[0]; floating */ + }; + struct { + __u8 fb_version; /* == 1, even => nfs_fhbase_old */ + __u8 fb_auth_type; + __u8 fb_fsid_type; + __u8 fb_fileid_type; + __u32 fb_auth_flex[]; /* flexible-array member */ + }; + }; };
struct knfsd_fh { @@ -97,7 +108,7 @@ struct knfsd_fh { #define fh_fsid_type fh_base.fh_new.fb_fsid_type #define fh_auth_type fh_base.fh_new.fb_auth_type #define fh_fileid_type fh_base.fh_new.fb_fileid_type -#define fh_fsid fh_base.fh_new.fb_auth +#define fh_fsid fh_base.fh_new.fb_auth_flex
/* Do not use, provided for userspace compatiblity. */ #define fh_auth fh_base.fh_new.fb_auth