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bh=bSXp7nzHYoO7ZnW+cTkiuZUZNBEqxN/Ogh463B22eJA=; b=QRcboZUJwnLMPUZoUoPnhCDbLqM70DLhWRQdOaAIQNv7t8rvy5xsDb4hQTR6iUjUyEtFvg CZAILvl8vYPPGKIp8Z9zzoaBKIrbSiSeuiZFk0zRZCklwt3VqLM7W6ePgiANW67EKVr4It 53Qor4HKqnM/S8mcM+EBL57td/GVhyM= X-MC-Unique: tU-yYX4WPsexLt4GDpZE5Q-1 From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, vgoyal@redhat.com, stefanha@redhat.com, virtio-fs@redhat.com Subject: [PATCH v2 3/6] tools/virtiofsd: xattr name mappings: Add option Date: Thu, 27 Aug 2020 16:36:54 +0100 Message-Id: <20200827153657.111098-4-dgilbert@redhat.com> In-Reply-To: <20200827153657.111098-1-dgilbert@redhat.com> References: <20200827153657.111098-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0.001 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" From: "Dr. David Alan Gilbert" Add an option to define mappings of xattr names so that the client and server filesystems see different views. This can be used to have different SELinux mappings as seen by the guest, to run the virtiofsd with less privileges (e.g. in a case where it can't set trusted/system/security xattrs but you want the guest to be able to), or to isolate multiple users of the same name; e.g. trusted attributes used by stacking overlayfs. A mapping engine is used wit 3 simple rules; the rules can be combined to allow most useful mapping scenarios. The ruleset is defined by -o xattrmap=3D'rules...'. This patch doesn't use the rule maps yet. Signed-off-by: Dr. David Alan Gilbert --- docs/tools/virtiofsd.rst | 55 ++++++++++++ tools/virtiofsd/passthrough_ll.c | 148 +++++++++++++++++++++++++++++++ 2 files changed, 203 insertions(+) diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst index 824e713491..2efa16d3c5 100644 --- a/docs/tools/virtiofsd.rst +++ b/docs/tools/virtiofsd.rst @@ -107,6 +107,60 @@ Options performance. ``auto`` acts similar to NFS with a 1 second metadata cache timeout. ``always`` sets a long cache lifetime at the expense of cohere= ncy. =20 +xattr-mapping +------------- + +By default the name of xattr's used by the client are passed through to th= e server +file system. This can be a problem where either those xattr names are used +by something on the server (e.g. selinux client/server confusion) or if the +virtiofsd is running in a container with restricted priviliges where it ca= nnot +access some attributes. + +A mapping of xattr names can be made using -o xattrmap=3Dmapping where the= ``mapping`` +string consists of a series of rules. + +The first matching rule terminates the mapping. + +Each rule consists of a number of fields separated with a separator that i= s the +first non-white space character in the rule. This separator must then be = used +for the whole rule. +White space may be added before and after each rule. +Using ':' as the separator a rule is of the form: + +``:scope:type:key:prepend:`` + +**scope** is: + +- 'client' - match 'key' against a xattr name from the client for + setxattr/getxattr/removexattr +- 'server' - match 'prepend' against a xattr name from the server + for listxattr +- 'all' - can be used to match both cases. + +**type** is one of: + +- 'prefix' - If 'key' matches the client then the 'prepend' + is added before the name is passed to the server. + For a server case, the prepend is tested and stripped + if matching. + +- 'ok' - The attribute name is OK and passed through to + the server unchanged. + +- 'bad' - If a client tries to use this name it's + denied using EPERM; when the server passes an attribute + name matching it's hidden. + +**key** is a string tested as a prefix on an attribute name originating +on the client. It maybe empty in which case a 'client' rule +will always match on client names. + +**prepend** is a string tested as a prefix on an attribute name originiati= ng +on the server, and used as a new prefix. It maybe empty +in which case a 'server' rule will always match on all names from +the server. + + Examples -------- =20 @@ -123,3 +177,4 @@ Export ``/var/lib/fs/vm001/`` on vhost-user UNIX domain= socket -numa node,memdev=3Dmem \ ... guest# mount -t virtiofs myfs /mnt + diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough= _ll.c index 083d17a960..00e96a10cd 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -64,6 +64,7 @@ #include #include =20 +#include "qemu/cutils.h" #include "passthrough_helpers.h" #include "passthrough_seccomp.h" =20 @@ -144,6 +145,7 @@ struct lo_data { int flock; int posix_lock; int xattr; + char *xattrmap; char *source; char *modcaps; double timeout; @@ -171,6 +173,7 @@ static const struct fuse_opt lo_opts[] =3D { { "no_posix_lock", offsetof(struct lo_data, posix_lock), 0 }, { "xattr", offsetof(struct lo_data, xattr), 1 }, { "no_xattr", offsetof(struct lo_data, xattr), 0 }, + { "xattrmap=3D%s", offsetof(struct lo_data, xattrmap), 0 }, { "modcaps=3D%s", offsetof(struct lo_data, modcaps), 0 }, { "timeout=3D%lf", offsetof(struct lo_data, timeout), 0 }, { "timeout=3D", offsetof(struct lo_data, timeout_set), 1 }, @@ -2003,6 +2006,146 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino= , struct fuse_file_info *fi, fuse_reply_err(req, res =3D=3D -1 ? errno : 0); } =20 +typedef struct xattr_map_entry { + const char *key; + const char *prepend; + unsigned int flags; +} XattrMapEntry; + +/* + * Exit; process attribute unmodified if matched. + * An empty key applies to all. + */ +#define XATTR_MAP_FLAG_END_OK (1 << 0) +/* + * The attribute is unwanted; + * EPERM on write hidden on read. + */ +#define XATTR_MAP_FLAG_END_BAD (1 << 1) +/* + * For attr that start with 'key' prepend 'prepend' + * 'key' maybe empty to prepend for all attrs + * key is defined from set/remove point of view. + * Automatically reversed on read + */ +#define XATTR_MAP_FLAG_PREFIX (1 << 2) +/* Apply rule to get/set/remove */ +#define XATTR_MAP_FLAG_CLIENT (1 << 16) +/* Apply rule to list */ +#define XATTR_MAP_FLAG_SERVER (1 << 17) +/* Apply rule to all */ +#define XATTR_MAP_FLAG_ALL (XATTR_MAP_FLAG_SERVER | XATTR_MAP_FLAG_CLIEN= T) + +static XattrMapEntry *xattr_map_list; + +static XattrMapEntry *parse_xattrmap(const char *map) +{ + XattrMapEntry *res =3D NULL; + size_t nentries =3D 0; + const char *tmp; + + while (*map) { + char sep; + + if (isspace(*map)) { + map++; + continue; + } + /* The separator is the first non-space of the rule */ + sep =3D *map++; + if (!sep) { + break; + } + + /* Allocate some space for the rule */ + res =3D g_realloc_n(res, ++nentries, sizeof(XattrMapEntry)); + res[nentries - 1].flags =3D 0; + + if (strstart(map, "client", &map)) { + res[nentries - 1].flags |=3D XATTR_MAP_FLAG_CLIENT; + } else if (strstart(map, "server", &map)) { + res[nentries - 1].flags |=3D XATTR_MAP_FLAG_SERVER; + } else if (strstart(map, "all", &map)) { + res[nentries - 1].flags |=3D XATTR_MAP_FLAG_ALL; + } else { + fuse_log(FUSE_LOG_ERR, + "%s: Unexpected scope;" + " Expecting 'client', 'server', or 'all', in rule %zu= \n", + __func__, nentries); + exit(1); + } + + + if (*map !=3D sep) { + fuse_log(FUSE_LOG_ERR, + "%s: Expecting '%c' found '%c'" + " after scope in rule %zu\n", + __func__, sep, *map, nentries + 1); + exit(1); + } + /* Skip the separator, now at the start of the 'type' */ + map++; + + /* Start of 'type' */ + if (strstart(map, "prefix", &map)) { + res[nentries - 1].flags |=3D XATTR_MAP_FLAG_PREFIX; + } else if (strstart(map, "ok", &map)) { + res[nentries - 1].flags |=3D XATTR_MAP_FLAG_END_OK; + } else if (strstart(map, "bad", &map)) { + res[nentries - 1].flags |=3D XATTR_MAP_FLAG_END_BAD; + } else { + fuse_log(FUSE_LOG_ERR, + "%s: Unexpected type;" + "Expecting 'prefix', 'ok', or 'bad' in rule %zu\n", + __func__, nentries); + exit(1); + } + + if (*map++ !=3D sep) { + fuse_log(FUSE_LOG_ERR, + "%s: Missing '%c' at end of type field of rule %zu\n", + __func__, sep, nentries); + exit(1); + } + + /* At start of 'key' field */ + tmp =3D strchr(map, sep); + if (!tmp) { + fuse_log(FUSE_LOG_ERR, + "%s: Missing '%c' at end of key field of rule %zu", + __func__, sep, nentries); + exit(1); + } + res[nentries - 1].key =3D g_strndup(map, tmp - map); + map =3D tmp + 1; + + /* At start of 'prepend' field */ + tmp =3D strchr(map, sep); + if (!tmp) { + fuse_log(FUSE_LOG_ERR, + "%s: Missing '%c' at end of prepend field of rule %zu= ", + __func__, sep, nentries); + exit(1); + } + res[nentries - 1].prepend =3D g_strndup(map, tmp - map); + map =3D tmp + 1; + /* End of rule - go around again for another rule */ + } + + if (!nentries) { + fuse_log(FUSE_LOG_ERR, "Empty xattr map\n"); + exit(1); + } + + /* Add a terminator to error in cases the user hasn't specified */ + res =3D g_realloc_n(res, ++nentries, sizeof(XattrMapEntry)); + res[nentries - 1].flags =3D XATTR_MAP_FLAG_ALL | XATTR_MAP_FLAG_END_BA= D; + res[nentries - 1].key =3D g_strdup(""); + res[nentries - 1].prepend =3D g_strdup(""); + + return res; +} + static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name, size_t size) { @@ -2909,6 +3052,11 @@ int main(int argc, char *argv[]) } else { lo.source =3D strdup("/"); } + + if (lo.xattrmap) { + xattr_map_list =3D parse_xattrmap(lo.xattrmap); + } + if (!lo.timeout_set) { switch (lo.cache) { case CACHE_NONE: --=20 2.26.2