On Jul 22, 2015, at 11:59 PM, Eric Sandeen <sandeen@xxxxxxxxxx> wrote:
>
> It's entirely possible for userspace to ask for an xattr which
> does not exist.
>
> Normally, there is no problem whatsoever when we ask for such
> a thing, but when we look at an obfuscated metadump image
> on a debug kernel with selinux, we trip over this ASSERT in
> xfs_da3_path_shift():
>
> *result = -ENOENT; /* we're out of our tree */
> ASSERT(args->op_flags & XFS_DA_OP_OKNOENT);
>
> It (more or less) only shows up in the above scenario, because
> xfs_metadump obfuscates attr names, but chooses names which
> keep the same hash value - and xfs_da3_node_lookup_int does:
>
> if (((retval == -ENOENT) || (retval == -ENOATTR)) &&
> (blk->hashval == args->hashval)) {
> error = xfs_da3_path_shift(state, &state->path, 1, 1,
> &retval);
Oh, and add: thanks to dchinner for spotting the above conditional that got us there ;)
-Eric
> IOWS, we only get down to the xfs_da3_path_shift() ASSERT
> if we are looking for an xattr which doesn't exist, but we
> find xattrs on disk which have the same hash, and so might be
> a hash collision, so we try the path shift. When *that*
> fails to find what we're looking for, we hit the assert about
> XFS_DA_OP_OKNOENT.
>
> Simply setting XFS_DA_OP_OKNOENT in xfs_attr_get solves this
> rather corner-case problem with no ill side effects. It's
> fine for an attr name lookup to fail.
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
>
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index 3349c9a..ff06557 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -139,6 +139,8 @@ xfs_attr_get(
>
> args.value = value;
> args.valuelen = *valuelenp;
> + /* Entirely possible to look up a name which doesn't exist */
> + args.op_flags = XFS_DA_OP_OKNOENT;
>
> lock_mode = xfs_ilock_attr_map_shared(ip);
> if (!xfs_inode_hasattr(ip))
>
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>
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