> On May 6, 2021, at 9:48 PM, NeilBrown <neilb@xxxxxxx> wrote:
>
>
> [[This is a proposed fix. It seems to work. I'd like
> some review comments before it is committed.
> Petr: it would be great if you could test it to confirm
> it actually works in your case.
> ]]
>
> Some filesystems cannot be exported without an fsid or uuid.
> tmpfs is the main example.
>
> When mountd creates nfsv4 pseudo-root exports for the path leading down
> to an export point it exports each directory without any fsid or uuid.
> If one of these directories is on tmp, that will fail.
>
> The net result is that exporting a subdirectory of a tmpfs filesystem
> will not work over NFSv4 as the parents within the filesystem cannot be
> exported. It will either fail, or fall-back to NFSv3 (depending on the
> version of the mount.nfs program).
>
> To fix this we need to provide an fsid or uuid for these pseudo-root
> exports. This patch does that by creating a UUID with the first 4 bytes
> 0xFFFFFFFF and the remaining 12 bytes form from the path name, xoring
> bytes together if the path is longer than 12 characters.
> Hopefully no filesystem uses a UUID like this....
That's not really a UUID, as per RFC 4122. I'm guessing it's possible
for a collision to occur pretty quickly, for instance. It would be nicer
if a conformant UUID could be used here.
Is there a problem with specifying the export's fsid in /etc/exports?
> The patch borrows some code from exportfs. Maybe that code should be
> move to a library..
>
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> support/export/v4root.c | 57 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 57 insertions(+)
>
> diff --git a/support/export/v4root.c b/support/export/v4root.c
> index 3654bd7c10c0..fd36eb704441 100644
> --- a/support/export/v4root.c
> +++ b/support/export/v4root.c
> @@ -11,6 +11,7 @@
> #include <config.h>
> #endif
>
> +#include <fcntl.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <sys/queue.h>
> @@ -21,6 +22,7 @@
> #include <unistd.h>
> #include <errno.h>
>
> +#include "nfsd_path.h"
> #include "xlog.h"
> #include "exportfs.h"
> #include "nfslib.h"
> @@ -73,6 +75,38 @@ set_pseudofs_security(struct exportent *pseudo)
> }
> }
>
> +static ssize_t exportfs_write(int fd, const char *buf, size_t len)
> +{
> + return nfsd_path_write(fd, buf, len);
> +}
> +
> +static int test_export(struct exportent *eep, int with_fsid)
> +{
> + char *path = eep->e_path;
> + int flags = eep->e_flags | (with_fsid ? NFSEXP_FSID : 0);
> + /* beside max path, buf size should take protocol str into account */
> + char buf[NFS_MAXPATHLEN+1+64] = { 0 };
> + char *bp = buf;
> + int len = sizeof(buf);
> + int fd, n;
> +
> + n = snprintf(buf, len, "-test-client- ");
> + bp += n;
> + len -= n;
> + qword_add(&bp, &len, path);
> + if (len < 1)
> + return 0;
> + snprintf(bp, len, " 3 %d 65534 65534 0\n", flags);
> + fd = open("/proc/net/rpc/nfsd.export/channel", O_WRONLY);
> + if (fd < 0)
> + return 0;
> + n = exportfs_write(fd, buf, strlen(buf));
> + close(fd);
> + if (n < 0)
> + return 0;
> + return 1;
> +}
> +
> /*
> * Create a pseudo export
> */
> @@ -82,6 +116,7 @@ v4root_create(char *path, nfs_export *export)
> nfs_export *exp;
> struct exportent eep;
> struct exportent *curexp = &export->m_export;
> + char uuid[33];
>
> dupexportent(&eep, &pseudo_root.m_export);
> eep.e_ttl = default_ttl;
> @@ -89,6 +124,28 @@ v4root_create(char *path, nfs_export *export)
> strncpy(eep.e_path, path, sizeof(eep.e_path)-1);
> if (strcmp(path, "/") != 0)
> eep.e_flags &= ~NFSEXP_FSID;
> + if (strcmp(path, "/") != 0 &&
> + !test_export(&eep, 0)) {
> + /* Need a uuid - base it on path */
> + char buf[12], *pp = path;
> + unsigned int i = 0;
> +
> + memset(buf, 0, sizeof(buf));
> + while (*pp) {
> + buf[i] ^= *pp++;
> + i += 1;
> + if (i >= sizeof(buf))
> + i = 0;
> + }
> + memset(uuid, 'F', 32);
> + uuid[32] = '\0';
> + pp = uuid + 32 - sizeof(buf) * 2;
> + for (i = 0; i < sizeof(buf); i++) {
> + snprintf(pp, 3, "%02X", buf[i]);
> + pp += 2;
> + }
> + eep.e_uuid = uuid;
> + }
> set_pseudofs_security(&eep);
> exp = export_create(&eep, 0);
> if (exp == NULL)
> --
> 2.31.1
>
--
Chuck Lever
