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H A Dxfs_symlink.cdiff ff627196ddc17a512d0c8db882fc2d4ef95b7217 Wed Dec 18 13:17:11 CST 2024 Darrick J. Wong <djwong@kernel.org> xfs: use consistent uid/gid when grabbing dquots for inodes

commit 24a4e1cb322e2bf0f3a1afd1978b610a23aa8f36 upstream.

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: c14329d39f2d ("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>
H A Dxfs_inode.cdiff ff627196ddc17a512d0c8db882fc2d4ef95b7217 Wed Dec 18 13:17:11 CST 2024 Darrick J. Wong <djwong@kernel.org> xfs: use consistent uid/gid when grabbing dquots for inodes

commit 24a4e1cb322e2bf0f3a1afd1978b610a23aa8f36 upstream.

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: c14329d39f2d ("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>