On Thu, Apr 03, 2014 at 04:46:52PM +1100, NeilBrown wrote:
>
> Hi,
> I came across an interesting issue recently.
>
> Suppose you have a filesystem which supports case-insensitive file names
> (like VFAT, but in this particular case 'NSS' - Novell Storage Services).
>
> And support you export some subdirectory (or sub-volume) using a
> non-canonical name.
> i.e. you "mkdir /path/export", the put "/path/EXPORT" in /etc/exports and
> mount server:/path/EXPORT from some client.
>
> This all works until the export cache times out and the kernel asks mountd
> if "/path/export" is exported. mountd says "no" and suddenly all accesses
> fail.
>
> I don't think much of case-insensitive file names, but I suspect we should
> either make this work, it issue a warning as to why it is failing.
> A simple work around is to export the canonical name and use it when
> mounting. But if the sysadmin doesn't know they need to, they are unlikely
> to guess.
>
> I don't think there is any API to test if a name is canonical, or to get the
> canonical name, so I cannot see any way in advance to see if this problem
> situation has arisen. So the only option I can think of is to fix it.
>
> The following patch (or something much like it for an older nfs-utils) seems
> to do the trick.
>
> What do people think? Is this a reasonable thing to do? Is it likely to
> have negative consequences that I haven't thought of?
Neat-o.
Are we adding a stat of every export in the export table where there
wasn't one before? But those should typically be cached, so maybe
there's no problem.
I'm not super-fond of the combining the comparison of two paths and
truncating of one into the same function, though I see why it's
convenient.
--b.
>
> Thanks,
> NeilBrown
>
>
>
> diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
> index 9a1bb2767ac2..2d91db76b867 100644
> --- a/utils/mountd/cache.c
> +++ b/utils/mountd/cache.c
> @@ -377,6 +377,28 @@ static char *next_mnt(void **v, char *p)
> return me->mnt_dir;
> }
>
> +static int same_path(char *child, char *parent, int len)
> +{
> + static char p[PATH_MAX];
> + struct stat sc, sp;
> + if (len <= 0)
> + len = strlen(child);
> + strncpy(p, child, len);
> + p[len] = 0;
> + if (strcmp(p, parent) == 0)
> + return 1;
> +
> + if (lstat(p, &sc) != 0)
> + return 0;
> + if (lstat(parent, &sp) != 0)
> + return 0;
> + if (sc.st_dev != sp.st_dev)
> + return 0;
> + if (sc.st_ino != sp.st_ino)
> + return 0;
> + return 1;
> +}
> +
> static int is_subdirectory(char *child, char *parent)
> {
> /* Check is child is strictly a subdirectory of
> @@ -387,7 +409,7 @@ static int is_subdirectory(char *child, char *parent)
> if (strcmp(parent, "/") == 0 && child[1] != 0)
> return 1;
>
> - return (strncmp(child, parent, l) == 0 && child[l] == '/');
> + return (same_path(child, parent, l) && child[l] == '/');
> }
>
> static int path_matches(nfs_export *exp, char *path)
> @@ -396,7 +418,7 @@ static int path_matches(nfs_export *exp, char *path)
> * exact match, or does the export have CROSSMOUNT, and path
> * is a descendant?
> */
> - return strcmp(path, exp->m_export.e_path) == 0
> + return same_path(path, exp->m_export.e_path, 0)
> || ((exp->m_export.e_flags & NFSEXP_CROSSMOUNT)
> && is_subdirectory(path, exp->m_export.e_path));
> }
--
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