On Thu, Feb 23, 2017 at 9:34 PM, J. Bruce Fields <bfields@xxxxxxxxxx> wrote:
> On Thu, Feb 23, 2017 at 03:52:14PM +0100, Andreas Gruenbacher wrote:
>> When querying for the buffer size required, a filesystem's getxattr
>> xattr handler or listxattr iop may return a value bigger than the
>> maximum size limit. However, the VFS will never return oversize
>> buffers, so cast such values to -E2BIG.
>>
>> Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx>
>> ---
>> fs/xattr.c | 20 ++++++++++++--------
>> 1 file changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/xattr.c b/fs/xattr.c
>> index 7e3317c..c19a163 100644
>> --- a/fs/xattr.c
>> +++ b/fs/xattr.c
>> @@ -537,16 +537,18 @@ getxattr(struct dentry *d, const char __user *name, void __user *value,
>> }
>>
>> error = vfs_getxattr(d, kname, kvalue, size);
>
> We have this just above:
>
> if (size) {
> if (size > XATTR_SIZE_MAX)
> size = XATTR_SIZE_MAX;
>
> So this test:
>
>> + if (error > XATTR_SIZE_MAX ||
>> + (error == -ERANGE && size >= XATTR_SIZE_MAX)) {
>> + /* The file system tried to returned a value bigger
>> + than XATTR_SIZE_MAX bytes. Not possible. */
>> + error = -E2BIG;
>> + }
>
> is equivalent to:
>
> if (error > XATTR_SIZE_MAX ||
> (error = -ERANGE && size == XATTR_SIZE_MAX))
>
> That's kind of a subtle case.
True.
> I guess the idea is that ERANGE means
> "the xattr value doesn't fit into the buffer you gave me", and E2BIG
> means "the xattr value couldn't fit in any buffer you could possible
> give me". And if the filesystem isn't satisfied even with a
> maximum-sized buffer then clearly we're in the second case. OK, got it.
> Still, this is a little subtle. I don't see EF2BIG in my copy of
> getxattr(2).
It's not in any of my copies of getxattr(2) either yet, but it will be soon :)
> Anyway, feel free to add
>
> Reviewed-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>
> but I wouldn't say no to more documentation.
Thanks,
Andreas
