| Message ID | 20200916163553.GA39212@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | virtiofsd: Add support for FUSE_HANDLE_KILLPRIV_V2 | expand |
On Wed, Sep 16, 2020 at 12:35:53PM -0400, Vivek Goyal wrote: > This patch adds basic support for FUSE_HANDLE_KILLPRIV_V2. virtiofsd > can enable/disable this by specifying option "-o killpriv_v2/no_killpriv_v2". > By default this is enabled as long as client supports it. > > I have posted corresponding kernel patches here. > > https://www.redhat.com/archives/virtio-fs/2020-September/msg00054.html I have posted of V3 of kernel patches now. This patch remains unchanged. https://lore.kernel.org/linux-fsdevel/20201009181512.65496-1-vgoyal@redhat.com/T/#m4a6ba7d6bc9defdde0882cf21b89b768ce837663 Thanks Vivek > > Signed-off-by: Vivek Goyal <vgoyal@redhat.com> > --- > include/standard-headers/linux/fuse.h | 10 ++- > tools/virtiofsd/fuse_common.h | 10 +++ > tools/virtiofsd/fuse_lowlevel.c | 10 ++- > tools/virtiofsd/fuse_lowlevel.h | 1 + > tools/virtiofsd/passthrough_ll.c | 116 ++++++++++++++++++++++++-- > 5 files changed, 136 insertions(+), 11 deletions(-) > > diff --git a/include/standard-headers/linux/fuse.h b/include/standard-headers/linux/fuse.h > index 26e7de1b43..744498bc5a 100644 > --- a/include/standard-headers/linux/fuse.h > +++ b/include/standard-headers/linux/fuse.h > @@ -338,6 +338,7 @@ struct fuse_file_lock { > #define FUSE_NO_OPENDIR_SUPPORT (1 << 24) > #define FUSE_EXPLICIT_INVAL_DATA (1 << 25) > #define FUSE_MAP_ALIGNMENT (1 << 26) > +#define FUSE_HANDLE_KILLPRIV_V2 (1 << 27) > > /** > * CUSE INIT request/reply flags > @@ -413,6 +414,13 @@ struct fuse_file_lock { > */ > #define FUSE_FSYNC_FDATASYNC (1 << 0) > > +/** > + * Open flags > + * FUSE_OPEN_KILL_PRIV: Kill suid/sgid/security.capability. sgid is cleared > + * only if file has group execute permission. > + */ > +#define FUSE_OPEN_KILL_PRIV (1 << 0) > + > enum fuse_opcode { > FUSE_LOOKUP = 1, > FUSE_FORGET = 2, /* no reply */ > @@ -579,7 +587,7 @@ struct fuse_setattr_in { > > struct fuse_open_in { > uint32_t flags; > - uint32_t unused; > + uint32_t open_flags; > }; > > struct fuse_create_in { > diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h > index aa7e6ed31a..a8d8217687 100644 > --- a/tools/virtiofsd/fuse_common.h > +++ b/tools/virtiofsd/fuse_common.h > @@ -352,6 +352,16 @@ struct fuse_file_info { > */ > #define FUSE_CAP_NO_OPENDIR_SUPPORT (1 << 24) > > +/** > + * Indicates that the filesystem is responsible for unsetting > + * setuid and setgid bits when a file is written, truncated, or > + * its owner is changed. setuid/setgid is cleared on WRITE/truncate > + * only if caller does not have CAP_FSETID. For WRITE requests > + * this is communicated through write flag FUSE_WRITE_KILL_PRIV. > + * > + */ > +#define FUSE_CAP_HANDLE_KILLPRIV_V2 (1 << 27) > + > /** > * Ioctl flags > * > diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c > index a34a611a90..90afffd6de 100644 > --- a/tools/virtiofsd/fuse_lowlevel.c > +++ b/tools/virtiofsd/fuse_lowlevel.c > @@ -881,7 +881,7 @@ static void do_setattr(fuse_req_t req, fuse_ino_t nodeid, > FUSE_SET_ATTR_GID | FUSE_SET_ATTR_SIZE | > FUSE_SET_ATTR_ATIME | FUSE_SET_ATTR_MTIME | > FUSE_SET_ATTR_ATIME_NOW | FUSE_SET_ATTR_MTIME_NOW | > - FUSE_SET_ATTR_CTIME; > + FUSE_SET_ATTR_CTIME | FUSE_SET_ATTR_KILL_PRIV; > > req->se->op.setattr(req, nodeid, &stbuf, arg->valid, fi); > } else { > @@ -1118,6 +1118,7 @@ static void do_open(fuse_req_t req, fuse_ino_t nodeid, > > memset(&fi, 0, sizeof(fi)); > fi.flags = arg->flags; > + fi.kill_priv = arg->open_flags & FUSE_OPEN_KILL_PRIV; > > if (req->se->op.open) { > req->se->op.open(req, nodeid, &fi); > @@ -2081,6 +2082,9 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, > bufsize = max_bufsize; > } > } > + if (arg->flags & FUSE_HANDLE_KILLPRIV_V2) { > + se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV_V2; > + } > #ifdef HAVE_SPLICE > #ifdef HAVE_VMSPLICE > se->conn.capable |= FUSE_CAP_SPLICE_WRITE | FUSE_CAP_SPLICE_MOVE; > @@ -2218,6 +2222,10 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, > outarg.map_alignment = ffsl(sysconf(_SC_PAGE_SIZE)) - 1; > } > > + if (se->conn.want & FUSE_CAP_HANDLE_KILLPRIV_V2) { > + outarg.flags |= FUSE_HANDLE_KILLPRIV_V2; > + } > + > fuse_log(FUSE_LOG_DEBUG, " INIT: %u.%u\n", outarg.major, outarg.minor); > fuse_log(FUSE_LOG_DEBUG, " flags=0x%08x\n", outarg.flags); > fuse_log(FUSE_LOG_DEBUG, " max_readahead=0x%08x\n", outarg.max_readahead); > diff --git a/tools/virtiofsd/fuse_lowlevel.h b/tools/virtiofsd/fuse_lowlevel.h > index d488b88882..fdc256b5ce 100644 > --- a/tools/virtiofsd/fuse_lowlevel.h > +++ b/tools/virtiofsd/fuse_lowlevel.h > @@ -145,6 +145,7 @@ struct fuse_forget_data { > #define FUSE_SET_ATTR_ATIME_NOW (1 << 7) > #define FUSE_SET_ATTR_MTIME_NOW (1 << 8) > #define FUSE_SET_ATTR_CTIME (1 << 10) > +#define FUSE_SET_ATTR_KILL_PRIV (1 << 14) > > /* > * Request methods and replies > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index 6514674f04..33f74a1a46 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -170,6 +170,7 @@ struct lo_data { > > /* An O_PATH file descriptor to /proc/self/fd/ */ > int proc_self_fd; > + int user_killpriv_v2, killpriv_v2; > }; > > static const struct fuse_opt lo_opts[] = { > @@ -192,6 +193,8 @@ static const struct fuse_opt lo_opts[] = { > { "no_shared", offsetof(struct lo_data, shared), 0 }, > { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 }, > { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 }, > + { "killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 1 }, > + { "no_killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 0 }, > FUSE_OPT_END > }; > static bool use_syslog = false; > @@ -588,6 +591,30 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) > fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling readdirplus\n"); > conn->want &= ~FUSE_CAP_READDIRPLUS; > } > + > + if (lo->user_killpriv_v2 == 1) { > + /* User explicitly asked for this option. Enable it unconditionally. > + * If connection does not have this capability, it should fail > + * in fuse_lowlevel.c > + */ > + fuse_log(FUSE_LOG_DEBUG, "lo_init: enabling killpriv_v2\n"); > + conn->want |= FUSE_CAP_HANDLE_KILLPRIV_V2; > + lo->killpriv_v2 = 1; > + } else if (lo->user_killpriv_v2 == -1 && > + conn->capable & FUSE_CAP_HANDLE_KILLPRIV_V2) { > + /* User did not specify a value for killpriv_v2. By default enable it > + * if connection offers this capability */ > + fuse_log(FUSE_LOG_DEBUG, "lo_init: enabling killpriv_v2\n"); > + conn->want |= FUSE_CAP_HANDLE_KILLPRIV_V2; > + lo->killpriv_v2 = 1; > + } else { > + /* Either user specified to disable killpriv_v2, or connection does > + * not offer this capability. Disable killpriv_v2 in both the cases > + */ > + fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling killpriv_v2\n"); > + conn->want &= ~FUSE_CAP_HANDLE_KILLPRIV_V2; > + lo->killpriv_v2 = 0; > + } > } > > static int64_t *version_ptr(struct lo_data *lo, struct lo_inode *inode) > @@ -686,6 +713,14 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr, > uid_t uid = (valid & FUSE_SET_ATTR_UID) ? attr->st_uid : (uid_t)-1; > gid_t gid = (valid & FUSE_SET_ATTR_GID) ? attr->st_gid : (gid_t)-1; > > + /* if fc->killpriv_v2 is set, change of ownership should clear > + * suid/sgid/caps. > + * > + * TODO: On ext4/xfs above works with fchownat() call without > + * doing anything extra. If there are filesystem where this > + * does not work, virtiofsd needs to take care of this. > + */ > + > res = fchownat(ifd, "", uid, gid, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW); > if (res == -1) { > goto out_err; > @@ -693,7 +728,18 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr, > } > if (valid & FUSE_SET_ATTR_SIZE) { > int truncfd; > - > + bool kill_priv = lo->killpriv_v2 && (valid & FUSE_SET_ATTR_KILL_PRIV); > + bool cap_fsetid_dropped = false; > + > + /* if fc->killpriv_v2 is set, change of size should clear caps > + * always. suid should be cleared if FUSE_SETATTR_KILL_PRIV is > + * set. And sgid should be cleared if FUSE_SETATTR_KILL_PRIV is > + * set as well as group execute permission is on. > + * > + * TODO: On ext4/xfs above works with truncate() call without > + * doing anything extra. If there are filesystem where this > + * does not work, virtiofsd needs to take care of this. > + */ > if (fi) { > truncfd = fd; > } else { > @@ -704,12 +750,26 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr, > } > } > > + if (kill_priv) { > + res = drop_effective_cap("FSETID", &cap_fsetid_dropped); > + if (res != 0) { > + lo_inode_put(lo, &inode); > + fuse_reply_err(req, res); > + } > + } > res = ftruncate(truncfd, attr->st_size); > + saverr = errno; > + if (cap_fsetid_dropped) { > + res = gain_effective_cap("FSETID"); > + if(res) { > + fuse_log(FUSE_LOG_ERR, "Failed to gain CAP_FSETID\n"); > + } > + } > if (!fi) { > - saverr = errno; > close(truncfd); > - errno = saverr; > } > + > + errno = saverr; > if (res == -1) { > goto out_err; > } > @@ -1943,20 +2003,45 @@ static void lo_fsyncdir(fuse_req_t req, fuse_ino_t ino, int datasync, > > static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi) > { > - int fd; > + int fd, ret, saverr; > ssize_t fh; > char buf[64]; > struct lo_data *lo = lo_data(req); > + bool cap_fsetid_dropped = false; > > - fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino, > - fi->flags); > + fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d, kill_priv=%d)" > + "\n", ino, fi->flags, fi->kill_priv); > > update_open_flags(lo->writeback, fi); > > sprintf(buf, "%i", lo_fd(req, ino)); > + > + /* > + * fi->kill_priv is set if file server opted for killpriv_v2 feature > + * and client did open(O_TRUNC) and caller did not have CAP_FSETID. > + * In that case suid/sgid/security.capability needs to be killed > + * according to certain rules. Dropping capability does right thing > + * on ext4/xfs already. > + */ > + if (fi->kill_priv) { > + ret = drop_effective_cap("FSETID", &cap_fsetid_dropped); > + if (ret != 0) { > + fuse_reply_err(req, ret); > + return; > + } > + } > + > fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); > + saverr = errno; > + if (cap_fsetid_dropped) { > + ret = gain_effective_cap("FSETID"); > + if (ret) { > + fuse_log(FUSE_LOG_ERR, "Failed to gain CAP_FSETID\n"); > + } > + } > + > if (fd == -1) { > - return (void)fuse_reply_err(req, errno); > + return (void)fuse_reply_err(req, saverr); > } > > pthread_mutex_lock(&lo->mutex); > @@ -2091,8 +2176,20 @@ static void lo_write_buf(fuse_req_t req, fuse_ino_t ino, > out_buf.buf[0].pos = off; > > fuse_log(FUSE_LOG_DEBUG, > - "lo_write_buf(ino=%" PRIu64 ", size=%zd, off=%lu)\n", ino, > - out_buf.buf[0].size, (unsigned long)off); > + "lo_write_buf(ino=%" PRIu64 ", size=%zd, off=%lu kill_priv=%d)\n", > + ino, out_buf.buf[0].size, (unsigned long)off, fi->kill_priv); > + > + /* > + * If lo->killpriv_v2 is set, then we are supposed to kill caps > + * and also kill suid/sgid if fi->kill_priv is set. Current > + * common filesystem ext4/xfs already drop security.capability > + * on WRITE. So we don't have to do anything special. > + * > + * TODO: If we are running on to of a file system which does not > + * remove caps on WRITE, then we will have to remove it ourselves > + * explicitly. Same is true for removing SUID/SGID if CAP_FSETID > + * is not there. > + */ > > /* > * If kill_priv is set, drop CAP_FSETID which should lead to kernel > @@ -3210,6 +3307,7 @@ int main(int argc, char *argv[]) > .writeback = 0, > .posix_lock = 1, > .proc_self_fd = -1, > + .user_killpriv_v2 = -1, > }; > struct lo_map_elem *root_elem; > int ret = -1; > -- > 2.25.4 > > _______________________________________________ > Virtio-fs mailing list > Virtio-fs@redhat.com > https://www.redhat.com/mailman/listinfo/virtio-fs
diff --git a/include/standard-headers/linux/fuse.h b/include/standard-headers/linux/fuse.h index 26e7de1b43..744498bc5a 100644 --- a/include/standard-headers/linux/fuse.h +++ b/include/standard-headers/linux/fuse.h @@ -338,6 +338,7 @@ struct fuse_file_lock { #define FUSE_NO_OPENDIR_SUPPORT (1 << 24) #define FUSE_EXPLICIT_INVAL_DATA (1 << 25) #define FUSE_MAP_ALIGNMENT (1 << 26) +#define FUSE_HANDLE_KILLPRIV_V2 (1 << 27) /** * CUSE INIT request/reply flags @@ -413,6 +414,13 @@ struct fuse_file_lock { */ #define FUSE_FSYNC_FDATASYNC (1 << 0) +/** + * Open flags + * FUSE_OPEN_KILL_PRIV: Kill suid/sgid/security.capability. sgid is cleared + * only if file has group execute permission. + */ +#define FUSE_OPEN_KILL_PRIV (1 << 0) + enum fuse_opcode { FUSE_LOOKUP = 1, FUSE_FORGET = 2, /* no reply */ @@ -579,7 +587,7 @@ struct fuse_setattr_in { struct fuse_open_in { uint32_t flags; - uint32_t unused; + uint32_t open_flags; }; struct fuse_create_in { diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h index aa7e6ed31a..a8d8217687 100644 --- a/tools/virtiofsd/fuse_common.h +++ b/tools/virtiofsd/fuse_common.h @@ -352,6 +352,16 @@ struct fuse_file_info { */ #define FUSE_CAP_NO_OPENDIR_SUPPORT (1 << 24) +/** + * Indicates that the filesystem is responsible for unsetting + * setuid and setgid bits when a file is written, truncated, or + * its owner is changed. setuid/setgid is cleared on WRITE/truncate + * only if caller does not have CAP_FSETID. For WRITE requests + * this is communicated through write flag FUSE_WRITE_KILL_PRIV. + * + */ +#define FUSE_CAP_HANDLE_KILLPRIV_V2 (1 << 27) + /** * Ioctl flags * diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c index a34a611a90..90afffd6de 100644 --- a/tools/virtiofsd/fuse_lowlevel.c +++ b/tools/virtiofsd/fuse_lowlevel.c @@ -881,7 +881,7 @@ static void do_setattr(fuse_req_t req, fuse_ino_t nodeid, FUSE_SET_ATTR_GID | FUSE_SET_ATTR_SIZE | FUSE_SET_ATTR_ATIME | FUSE_SET_ATTR_MTIME | FUSE_SET_ATTR_ATIME_NOW | FUSE_SET_ATTR_MTIME_NOW | - FUSE_SET_ATTR_CTIME; + FUSE_SET_ATTR_CTIME | FUSE_SET_ATTR_KILL_PRIV; req->se->op.setattr(req, nodeid, &stbuf, arg->valid, fi); } else { @@ -1118,6 +1118,7 @@ static void do_open(fuse_req_t req, fuse_ino_t nodeid, memset(&fi, 0, sizeof(fi)); fi.flags = arg->flags; + fi.kill_priv = arg->open_flags & FUSE_OPEN_KILL_PRIV; if (req->se->op.open) { req->se->op.open(req, nodeid, &fi); @@ -2081,6 +2082,9 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, bufsize = max_bufsize; } } + if (arg->flags & FUSE_HANDLE_KILLPRIV_V2) { + se->conn.capable |= FUSE_CAP_HANDLE_KILLPRIV_V2; + } #ifdef HAVE_SPLICE #ifdef HAVE_VMSPLICE se->conn.capable |= FUSE_CAP_SPLICE_WRITE | FUSE_CAP_SPLICE_MOVE; @@ -2218,6 +2222,10 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid, outarg.map_alignment = ffsl(sysconf(_SC_PAGE_SIZE)) - 1; } + if (se->conn.want & FUSE_CAP_HANDLE_KILLPRIV_V2) { + outarg.flags |= FUSE_HANDLE_KILLPRIV_V2; + } + fuse_log(FUSE_LOG_DEBUG, " INIT: %u.%u\n", outarg.major, outarg.minor); fuse_log(FUSE_LOG_DEBUG, " flags=0x%08x\n", outarg.flags); fuse_log(FUSE_LOG_DEBUG, " max_readahead=0x%08x\n", outarg.max_readahead); diff --git a/tools/virtiofsd/fuse_lowlevel.h b/tools/virtiofsd/fuse_lowlevel.h index d488b88882..fdc256b5ce 100644 --- a/tools/virtiofsd/fuse_lowlevel.h +++ b/tools/virtiofsd/fuse_lowlevel.h @@ -145,6 +145,7 @@ struct fuse_forget_data { #define FUSE_SET_ATTR_ATIME_NOW (1 << 7) #define FUSE_SET_ATTR_MTIME_NOW (1 << 8) #define FUSE_SET_ATTR_CTIME (1 << 10) +#define FUSE_SET_ATTR_KILL_PRIV (1 << 14) /* * Request methods and replies diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c index 6514674f04..33f74a1a46 100644 --- a/tools/virtiofsd/passthrough_ll.c +++ b/tools/virtiofsd/passthrough_ll.c @@ -170,6 +170,7 @@ struct lo_data { /* An O_PATH file descriptor to /proc/self/fd/ */ int proc_self_fd; + int user_killpriv_v2, killpriv_v2; }; static const struct fuse_opt lo_opts[] = { @@ -192,6 +193,8 @@ static const struct fuse_opt lo_opts[] = { { "no_shared", offsetof(struct lo_data, shared), 0 }, { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 }, { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 }, + { "killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 1 }, + { "no_killpriv_v2", offsetof(struct lo_data, user_killpriv_v2), 0 }, FUSE_OPT_END }; static bool use_syslog = false; @@ -588,6 +591,30 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn) fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling readdirplus\n"); conn->want &= ~FUSE_CAP_READDIRPLUS; } + + if (lo->user_killpriv_v2 == 1) { + /* User explicitly asked for this option. Enable it unconditionally. + * If connection does not have this capability, it should fail + * in fuse_lowlevel.c + */ + fuse_log(FUSE_LOG_DEBUG, "lo_init: enabling killpriv_v2\n"); + conn->want |= FUSE_CAP_HANDLE_KILLPRIV_V2; + lo->killpriv_v2 = 1; + } else if (lo->user_killpriv_v2 == -1 && + conn->capable & FUSE_CAP_HANDLE_KILLPRIV_V2) { + /* User did not specify a value for killpriv_v2. By default enable it + * if connection offers this capability */ + fuse_log(FUSE_LOG_DEBUG, "lo_init: enabling killpriv_v2\n"); + conn->want |= FUSE_CAP_HANDLE_KILLPRIV_V2; + lo->killpriv_v2 = 1; + } else { + /* Either user specified to disable killpriv_v2, or connection does + * not offer this capability. Disable killpriv_v2 in both the cases + */ + fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling killpriv_v2\n"); + conn->want &= ~FUSE_CAP_HANDLE_KILLPRIV_V2; + lo->killpriv_v2 = 0; + } } static int64_t *version_ptr(struct lo_data *lo, struct lo_inode *inode) @@ -686,6 +713,14 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr, uid_t uid = (valid & FUSE_SET_ATTR_UID) ? attr->st_uid : (uid_t)-1; gid_t gid = (valid & FUSE_SET_ATTR_GID) ? attr->st_gid : (gid_t)-1; + /* if fc->killpriv_v2 is set, change of ownership should clear + * suid/sgid/caps. + * + * TODO: On ext4/xfs above works with fchownat() call without + * doing anything extra. If there are filesystem where this + * does not work, virtiofsd needs to take care of this. + */ + res = fchownat(ifd, "", uid, gid, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW); if (res == -1) { goto out_err; @@ -693,7 +728,18 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr, } if (valid & FUSE_SET_ATTR_SIZE) { int truncfd; - + bool kill_priv = lo->killpriv_v2 && (valid & FUSE_SET_ATTR_KILL_PRIV); + bool cap_fsetid_dropped = false; + + /* if fc->killpriv_v2 is set, change of size should clear caps + * always. suid should be cleared if FUSE_SETATTR_KILL_PRIV is + * set. And sgid should be cleared if FUSE_SETATTR_KILL_PRIV is + * set as well as group execute permission is on. + * + * TODO: On ext4/xfs above works with truncate() call without + * doing anything extra. If there are filesystem where this + * does not work, virtiofsd needs to take care of this. + */ if (fi) { truncfd = fd; } else { @@ -704,12 +750,26 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr, } } + if (kill_priv) { + res = drop_effective_cap("FSETID", &cap_fsetid_dropped); + if (res != 0) { + lo_inode_put(lo, &inode); + fuse_reply_err(req, res); + } + } res = ftruncate(truncfd, attr->st_size); + saverr = errno; + if (cap_fsetid_dropped) { + res = gain_effective_cap("FSETID"); + if(res) { + fuse_log(FUSE_LOG_ERR, "Failed to gain CAP_FSETID\n"); + } + } if (!fi) { - saverr = errno; close(truncfd); - errno = saverr; } + + errno = saverr; if (res == -1) { goto out_err; } @@ -1943,20 +2003,45 @@ static void lo_fsyncdir(fuse_req_t req, fuse_ino_t ino, int datasync, static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi) { - int fd; + int fd, ret, saverr; ssize_t fh; char buf[64]; struct lo_data *lo = lo_data(req); + bool cap_fsetid_dropped = false; - fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n", ino, - fi->flags); + fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d, kill_priv=%d)" + "\n", ino, fi->flags, fi->kill_priv); update_open_flags(lo->writeback, fi); sprintf(buf, "%i", lo_fd(req, ino)); + + /* + * fi->kill_priv is set if file server opted for killpriv_v2 feature + * and client did open(O_TRUNC) and caller did not have CAP_FSETID. + * In that case suid/sgid/security.capability needs to be killed + * according to certain rules. Dropping capability does right thing + * on ext4/xfs already. + */ + if (fi->kill_priv) { + ret = drop_effective_cap("FSETID", &cap_fsetid_dropped); + if (ret != 0) { + fuse_reply_err(req, ret); + return; + } + } + fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW); + saverr = errno; + if (cap_fsetid_dropped) { + ret = gain_effective_cap("FSETID"); + if (ret) { + fuse_log(FUSE_LOG_ERR, "Failed to gain CAP_FSETID\n"); + } + } + if (fd == -1) { - return (void)fuse_reply_err(req, errno); + return (void)fuse_reply_err(req, saverr); } pthread_mutex_lock(&lo->mutex); @@ -2091,8 +2176,20 @@ static void lo_write_buf(fuse_req_t req, fuse_ino_t ino, out_buf.buf[0].pos = off; fuse_log(FUSE_LOG_DEBUG, - "lo_write_buf(ino=%" PRIu64 ", size=%zd, off=%lu)\n", ino, - out_buf.buf[0].size, (unsigned long)off); + "lo_write_buf(ino=%" PRIu64 ", size=%zd, off=%lu kill_priv=%d)\n", + ino, out_buf.buf[0].size, (unsigned long)off, fi->kill_priv); + + /* + * If lo->killpriv_v2 is set, then we are supposed to kill caps + * and also kill suid/sgid if fi->kill_priv is set. Current + * common filesystem ext4/xfs already drop security.capability + * on WRITE. So we don't have to do anything special. + * + * TODO: If we are running on to of a file system which does not + * remove caps on WRITE, then we will have to remove it ourselves + * explicitly. Same is true for removing SUID/SGID if CAP_FSETID + * is not there. + */ /* * If kill_priv is set, drop CAP_FSETID which should lead to kernel @@ -3210,6 +3307,7 @@ int main(int argc, char *argv[]) .writeback = 0, .posix_lock = 1, .proc_self_fd = -1, + .user_killpriv_v2 = -1, }; struct lo_map_elem *root_elem; int ret = -1;
This patch adds basic support for FUSE_HANDLE_KILLPRIV_V2. virtiofsd can enable/disable this by specifying option "-o killpriv_v2/no_killpriv_v2". By default this is enabled as long as client supports it. I have posted corresponding kernel patches here. https://www.redhat.com/archives/virtio-fs/2020-September/msg00054.html Signed-off-by: Vivek Goyal <vgoyal@redhat.com> --- include/standard-headers/linux/fuse.h | 10 ++- tools/virtiofsd/fuse_common.h | 10 +++ tools/virtiofsd/fuse_lowlevel.c | 10 ++- tools/virtiofsd/fuse_lowlevel.h | 1 + tools/virtiofsd/passthrough_ll.c | 116 ++++++++++++++++++++++++-- 5 files changed, 136 insertions(+), 11 deletions(-)