linux-ext4 - [PATCH 1/2] ext4: use XATTR_CREATE in ext4

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Date:   Thu, 26 Apr 2018 19:20:26 +0800
From:   Eryu Guan <guaneryu@...il.com>
To:     linux-ext4@...r.kernel.org
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        Theodore Ts'o <tytso@....edu>,
        Tahsin Erdogan <tahsin@...gle.com>,
        Eryu Guan <guaneryu@...il.com>
Subject: [PATCH 1/2] ext4: use XATTR_CREATE in ext4_initxattrs()

I hit ENOSPC error when creating new file in a newly created ext4
with ea_inode feature enabled, if selinux is enabled and ext4 is
mounted without any selinux context. e.g.

  mkfs -t ext4 -O ea_inode -F /dev/sda5
  mount /dev/sda5 /mnt/ext4
  touch /mnt/ext4/testfile  # got ENOSPC here

It turns out that we run out of journal credits in
ext4_xattr_set_handle() when creating new selinux label for the
newly created inode.

This is because that in __ext4_new_inode() we use
__ext4_xattr_set_credits() to calculate the reserved credits for new
xattr, with the 'is_create' argument being true, which implies less
credits in the ea_inode case. But we calculate the required credits
in ext4_xattr_set_handle() with 'is_create' being false, which means
we need more credits if ea_inode feature is enabled. So we don't
have enough credits and error out with ENOSPC.

Fix it by simply calling ext4_xattr_set_handle() with XATTR_CREATE
flag in ext4_initxattrs(), so we end up with requiring less credits
than reserved. The semantic of XATTR_CREATE is "Perform a pure
create, which fails if the named attribute exists already." (from
setxattr(2)), which is fine in this case, because we only call
ext4_initxattrs() on newly created inode.

Fixes: af65207c76ce ("ext4: fix __ext4_new_inode() journal credits calculation")
Cc: Tahsin Erdogan <tahsin@...gle.com>
Signed-off-by: Eryu Guan <guaneryu@...il.com>
---
 fs/ext4/xattr_security.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/xattr_security.c b/fs/ext4/xattr_security.c
index 629001b28632..197a9d8a15ef 100644
--- a/fs/ext4/xattr_security.c
+++ b/fs/ext4/xattr_security.c
@@ -43,7 +43,7 @@ ext4_initxattrs(struct inode *inode, const struct xattr *xattr_array,
 		err = ext4_xattr_set_handle(handle, inode,
 					    EXT4_XATTR_INDEX_SECURITY,
 					    xattr->name, xattr->value,
-					    xattr->value_len, 0);
+					    xattr->value_len, XATTR_CREATE);
 		if (err < 0)
 			break;
 	}
-- 
2.14.3