Btrfs devel - Oct 2011 - [PATCH] Btrfs: fix regression in re-setting a large xattr

Recently I changed the xattr stuff to unconditionally set the xattr first in
case the xattr didn''t exist yet.  This has introduced a regression when
setting
an xattr that already exists with a large value.  If we find the key we are
looking for split_leaf will assume that we''re extending that item.  The
problem
is the size we pass down to btrfs_search_slot includes the size of the item
already, so if we have the largest xattr we can possibly have plus the size of
the xattr item plus the xattr item that btrfs_search_slot we''d overflow
the
leaf.  Thankfully this is not what we''re doing, but split_leaf
doesn''t know this
so it just returns EOVERFLOW.  So in the xattr code we need to check and see if
we got back EOVERFLOW and treat it like EEXIST since that''s really what
happened.  Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
---
 fs/btrfs/xattr.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
index 69565e5..5bd7877 100644
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -127,7 +127,18 @@ static int do_setxattr(struct btrfs_trans_handle *trans,
 again:
 	ret = btrfs_insert_xattr_item(trans, root, path, btrfs_ino(inode),
 				      name, name_len, value, size);
-	if (ret == -EEXIST) {
+	/*
+	 * If we''re setting an xattr to a new value but the new value is say
+	 * exactly BTRFS_MAX_XATTR_SIZE, we could end up with EOVERFLOW getting
+	 * back from split_leaf.  This is because it thinks we''ll be
extending
+	 * the existing item size, but we''re asking for enough space to add
the
+	 * item itself.  So if we get EOVERFLOW just set ret to EEXIST and let
+	 * the rest of the function figure it out.
+	 */
+	if (ret == -EOVERFLOW)
+		ret = -EEXIST;
+
+	if (ret == -EEXIST || ret == -EOVERFLOW) {
 		if (flags & XATTR_CREATE)
 			goto out;
 		/*
-- 
1.7.5.2

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(2011/10/14 2:11), Josef Bacik wrote:
> Recently I changed the xattr stuff to unconditionally set the xattr first
in
> case the xattr didn''t exist yet.  This has introduced a regression
when setting
> an xattr that already exists with a large value.  If we find the key we are
> looking for split_leaf will assume that we''re extending that item.
The problem
> is the size we pass down to btrfs_search_slot includes the size of the item
> already, so if we have the largest xattr we can possibly have plus the size
of
> the xattr item plus the xattr item that btrfs_search_slot we''d
overflow the
> leaf.  Thankfully this is not what we''re doing, but split_leaf
doesn''t know this
> so it just returns EOVERFLOW.  So in the xattr code we need to check and
see if
> we got back EOVERFLOW and treat it like EEXIST since that''s really
what
> happened.  Thanks,
> 
> Signed-off-by: Josef Bacik <josef@redhat.com>
> ---
>  fs/btrfs/xattr.c |   13 ++++++++++++-
>  1 files changed, 12 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> index 69565e5..5bd7877 100644
> --- a/fs/btrfs/xattr.c
> +++ b/fs/btrfs/xattr.c
> @@ -127,7 +127,18 @@ static int do_setxattr(struct btrfs_trans_handle
*trans,
>  again:
>  	ret = btrfs_insert_xattr_item(trans, root, path, btrfs_ino(inode),
>  				      name, name_len, value, size);
> -	if (ret == -EEXIST) {
> +	/*
> +	 * If we''re setting an xattr to a new value but the new value is
say
> +	 * exactly BTRFS_MAX_XATTR_SIZE, we could end up with EOVERFLOW getting
> +	 * back from split_leaf.  This is because it thinks we''ll be
extending
> +	 * the existing item size, but we''re asking for enough space to
add the
> +	 * item itself.  So if we get EOVERFLOW just set ret to EEXIST and let
> +	 * the rest of the function figure it out.
> +	 */
> +	if (ret == -EOVERFLOW)
> +		ret = -EEXIST;
> +
> +	if (ret == -EEXIST || ret == -EOVERFLOW) {
Why tested again EOVERFLOW?

Thanks,
Tsutomu
>  		if (flags & XATTR_CREATE)
>  			goto out;
>  		/*
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On Fri, Oct 14, 2011 at 09:04:28AM +0900, Tsutomu Itoh
wrote:
> (2011/10/14 2:11), Josef Bacik wrote:
> > Recently I changed the xattr stuff to unconditionally set the xattr
first in
> > case the xattr didn''t exist yet.  This has introduced a
regression when setting
> > an xattr that already exists with a large value.  If we find the key
we are
> > looking for split_leaf will assume that we''re extending that
item.  The problem
> > is the size we pass down to btrfs_search_slot includes the size of the
item
> > already, so if we have the largest xattr we can possibly have plus the
size of
> > the xattr item plus the xattr item that btrfs_search_slot
we''d overflow the
> > leaf.  Thankfully this is not what we''re doing, but
split_leaf doesn''t know this
> > so it just returns EOVERFLOW.  So in the xattr code we need to check
and see if
> > we got back EOVERFLOW and treat it like EEXIST since that''s
really what
> > happened.  Thanks,
> > 
> > Signed-off-by: Josef Bacik <josef@redhat.com>
> > ---
> >  fs/btrfs/xattr.c |   13 ++++++++++++-
> >  1 files changed, 12 insertions(+), 1 deletions(-)
> > 
> > diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> > index 69565e5..5bd7877 100644
> > --- a/fs/btrfs/xattr.c
> > +++ b/fs/btrfs/xattr.c
> > @@ -127,7 +127,18 @@ static int do_setxattr(struct btrfs_trans_handle
*trans,
> >  again:
> >  	ret = btrfs_insert_xattr_item(trans, root, path, btrfs_ino(inode),
> >  				      name, name_len, value, size);
> > -	if (ret == -EEXIST) {
> > +	/*
> > +	 * If we''re setting an xattr to a new value but the new
value is say
> > +	 * exactly BTRFS_MAX_XATTR_SIZE, we could end up with EOVERFLOW
getting
> > +	 * back from split_leaf.  This is because it thinks we''ll
be extending
> > +	 * the existing item size, but we''re asking for enough
space to add the
> > +	 * item itself.  So if we get EOVERFLOW just set ret to EEXIST and
let
> > +	 * the rest of the function figure it out.
> > +	 */
> > +	if (ret == -EOVERFLOW)
> > +		ret = -EEXIST;
> > +
> > +	if (ret == -EEXIST || ret == -EOVERFLOW) {
> 
> Why tested again EOVERFLOW?
> 
Oops thats my fault, I had thought to check for eoverflow but then thought
better to just set it to eexist and didn''t fix the first thought. 
I''ll send out
a fix.  Thanks,

Josef
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