xfs: use consistent uid/gid when grabbing dquots for inodes

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[ Upstream commit  24a4e1cb32 ]

[ 6.1: resolved conflicts in xfs_inode.c and xfs_symlink.c due to 6.1
not having switched to idmap yet ]

I noticed that callers of xfs_qm_vop_dqalloc use the following code to
compute the anticipated uid of the new file:

	mapped_fsuid(idmap, &init_user_ns);

whereas the VFS uses a slightly different computation for actually
assigning i_uid:

	mapped_fsuid(idmap, i_user_ns(inode));

Technically, these are not the same things.  According to Christian
Brauner, the only time that inode->i_sb->s_user_ns != &init_user_ns is
when the filesystem was mounted in a new mount namespace by an
unpriviledged user.  XFS does not allow this, which is why we've never
seen bug reports about quotas being incorrect or the uid checks in
xfs_qm_vop_create_dqattach tripping debug assertions.

However, this /is/ a logic bomb, so let's make the code consistent.

Link: https://lore.kernel.org/linux-fsdevel/20240617-weitblick-gefertigt-4a41f37119fa@brauner/
Fixes: c14329d39f ("fs: port fs{g,u}id helpers to mnt_idmap")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

...

This commit is contained in:

Darrick J. Wong 2025-06-11 14:01:15 -07:00 • committed by Greg Kroah-Hartman

parent 5c646ec784

commit bfaa06ea81

2 changed files with 15 additions and 9 deletions

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16

fs/xfs/xfs_inode.c

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8

fs/xfs/xfs_symlink.c

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