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

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>

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index a4e3cd8971fc6e6043ee7ddf5b0f203c2042c52e..fd1a59af6cbbc20bcd466c820b339f2a217dd5c9 100644 (file)
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -1059,10 +1059,12 @@ xfs_create(
        prid = xfs_get_initial_prid(dp);
 
        /*
-        * Make sure that we have allocated dquot(s) on disk.
+        * Make sure that we have allocated dquot(s) on disk.  The uid/gid
+        * computation code must match what the VFS uses to assign i_[ug]id.
+        * INHERIT adjusts the gid computation for setgid/grpid systems.
         */
-       error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, &init_user_ns),
-                       mapped_fsgid(idmap, &init_user_ns), prid,
+       error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, i_user_ns(VFS_I(dp))),
+                       mapped_fsgid(idmap, i_user_ns(VFS_I(dp))), prid,
                        XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
                        &udqp, &gdqp, &pdqp);
        if (error)
@@ -1234,10 +1236,12 @@ xfs_create_tmpfile(
        prid = xfs_get_initial_prid(dp);
 
        /*
-        * Make sure that we have allocated dquot(s) on disk.
+        * Make sure that we have allocated dquot(s) on disk.  The uid/gid
+        * computation code must match what the VFS uses to assign i_[ug]id.
+        * INHERIT adjusts the gid computation for setgid/grpid systems.
         */
-       error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, &init_user_ns),
-                       mapped_fsgid(idmap, &init_user_ns), prid,
+       error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, i_user_ns(VFS_I(dp))),
+                       mapped_fsgid(idmap, i_user_ns(VFS_I(dp))), prid,
                        XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
                        &udqp, &gdqp, &pdqp);
        if (error)

diff --git a/fs/xfs/xfs_symlink.c b/fs/xfs/xfs_symlink.c
index 17aee806ec2e1c7296f255cd274326ca1015e88b..53ed512c6f21115c530e115d4446c07681484bfc 100644 (file)
--- a/fs/xfs/xfs_symlink.c
+++ b/fs/xfs/xfs_symlink.c
@@ -122,10 +122,12 @@ xfs_symlink(
        prid = xfs_get_initial_prid(dp);
 
        /*
-        * Make sure that we have allocated dquot(s) on disk.
+        * Make sure that we have allocated dquot(s) on disk.  The uid/gid
+        * computation code must match what the VFS uses to assign i_[ug]id.
+        * INHERIT adjusts the gid computation for setgid/grpid systems.
         */
-       error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, &init_user_ns),
-                       mapped_fsgid(idmap, &init_user_ns), prid,
+       error = xfs_qm_vop_dqalloc(dp, mapped_fsuid(idmap, i_user_ns(VFS_I(dp))),
+                       mapped_fsgid(idmap, i_user_ns(VFS_I(dp))), prid,
                        XFS_QMOPT_QUOTALL | XFS_QMOPT_INHERIT,
                        &udqp, &gdqp, &pdqp);
        if (error)