On 04/03/2014 04:09 PM, J. Bruce Fields wrote:
> 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;
>> +
Addressing Bruce concern, perhaps you would like to
also stricmp the names, so to not lstat on all export
entries.
+ if (stricmp(p, parent) =! 0)
+ return 0;
>> + 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;
Hard links on directories any one ? ;-)
Thanks
Boaz
>> + 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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