fs: fix acl translation

BugLink: https://bugs.launchpad.net/bugs/1986724
commit 705191b03d507744c7e097f78d583621c14988ac upstream.

Last cycle we extended the idmapped mounts infrastructure to support
idmapped mounts of idmapped filesystems (No such filesystem yet exist.).
Since then, the meaning of an idmapped mount is a mount whose idmapping
is different from the filesystems idmapping.

While doing that work we missed to adapt the acl translation helpers.
They still assume that checking for the identity mapping is enough.  But
they need to use the no_idmapping() helper instead.

Note, POSIX ACLs are always translated right at the userspace-kernel
boundary using the caller's current idmapping and the initial idmapping.
The order depends on whether we're coming from or going to userspace.
The filesystem's idmapping doesn't matter at the border.

Consequently, if a non-idmapped mount is passed we need to make sure to
always pass the initial idmapping as the mount's idmapping and not the
filesystem idmapping.  Since it's irrelevant here it would yield invalid
ids and prevent setting acls for filesystems that are mountable in a
userns and support posix acls (tmpfs and fuse).

I verified the regression reported in [1] and verified that this patch
fixes it.  A regression test will be added to xfstests in parallel.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=215849
Fixes: bd303368b776 ("fs: support mapped mounts of mapped filesystems")
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: <stable@vger.kernel.org> # 5.15+
Cc: <regressions@lists.linux.dev>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index d6c7b620fb8f7c7413239e1cf10bebfe413b4143..ceb1e3b868577ce9e535ab8a6a0507dd7ebddd3f 100644 (file)
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -760,9 +760,14 @@ static void posix_acl_fix_xattr_userns(
 }
 
 void posix_acl_fix_xattr_from_user(struct user_namespace *mnt_userns,
+                                  struct inode *inode,
                                   void *value, size_t size)
 {
        struct user_namespace *user_ns = current_user_ns();
+
+       /* Leave ids untouched on non-idmapped mounts. */
+       if (no_idmapping(mnt_userns, i_user_ns(inode)))
+               mnt_userns = &init_user_ns;
        if ((user_ns == &init_user_ns) && (mnt_userns == &init_user_ns))
                return;
        posix_acl_fix_xattr_userns(&init_user_ns, user_ns, mnt_userns, value,
@@ -770,9 +775,14 @@ void posix_acl_fix_xattr_from_user(struct user_namespace *mnt_userns,
 }
 
 void posix_acl_fix_xattr_to_user(struct user_namespace *mnt_userns,
+                                struct inode *inode,
                                 void *value, size_t size)
 {
        struct user_namespace *user_ns = current_user_ns();
+
+       /* Leave ids untouched on non-idmapped mounts. */
+       if (no_idmapping(mnt_userns, i_user_ns(inode)))
+               mnt_userns = &init_user_ns;
        if ((user_ns == &init_user_ns) && (mnt_userns == &init_user_ns))
                return;
        posix_acl_fix_xattr_userns(user_ns, &init_user_ns, mnt_userns, value,

diff --git a/fs/xattr.c b/fs/xattr.c
index 8cff77db8192c3c19b970ceff71f56422f7aab2d..d1407f5c289484d97134e4f4dcdfa47742dd162d 100644 (file)
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -594,7 +594,8 @@ setxattr(struct user_namespace *mnt_userns, struct dentry *d,
                }
                if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
                    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
-                       posix_acl_fix_xattr_from_user(mnt_userns, kvalue, size);
+                       posix_acl_fix_xattr_from_user(mnt_userns, d_inode(d),
+                                                     kvalue, size);
        }
 
        error = vfs_setxattr(mnt_userns, d, kname, kvalue, size, flags);
@@ -692,7 +693,8 @@ getxattr(struct user_namespace *mnt_userns, struct dentry *d,
        if (error > 0) {
                if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
                    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
-                       posix_acl_fix_xattr_to_user(mnt_userns, kvalue, error);
+                       posix_acl_fix_xattr_to_user(mnt_userns, d_inode(d),
+                                                   kvalue, error);
                if (size && copy_to_user(value, kvalue, error))
                        error = -EFAULT;
        } else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {

diff --git a/include/linux/posix_acl_xattr.h b/include/linux/posix_acl_xattr.h
index 060e8d2031814404175c8635c9a6184ed2d7e885..1766e1de695600968b9501c7d51d6a4db00b53a3 100644 (file)
--- a/include/linux/posix_acl_xattr.h
+++ b/include/linux/posix_acl_xattr.h
@@ -34,15 +34,19 @@ posix_acl_xattr_count(size_t size)
 
 #ifdef CONFIG_FS_POSIX_ACL
 void posix_acl_fix_xattr_from_user(struct user_namespace *mnt_userns,
+                                  struct inode *inode,
                                   void *value, size_t size);
 void posix_acl_fix_xattr_to_user(struct user_namespace *mnt_userns,
+                                  struct inode *inode,
                                 void *value, size_t size);
 #else
 static inline void posix_acl_fix_xattr_from_user(struct user_namespace *mnt_userns,
+                                                struct inode *inode,
                                                 void *value, size_t size)
 {
 }
 static inline void posix_acl_fix_xattr_to_user(struct user_namespace *mnt_userns,
+                                              struct inode *inode,
                                               void *value, size_t size)
 {
 }