fs: fix acl translation

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: 92dfa4fb006d ("fs: support mapped mounts of mapped filesystems")
Cc: Seth Forshee <sforshee@digitalocean.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: <stable@vger.kernel.org> # 5.17
Cc: <regressions@lists.linux.dev>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 80acb6885cf90b6fce2aa5b64d7b6c3b10d6687a..962d32468eb487afd42a14da7afd7589aaeaac98 100644 (file)
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -759,9 +759,14 @@ 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,
@@ -769,9 +774,14 @@ 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 5c8c5175b385c274eaac9a239ba0749b9372ff98..998045165916edcd1f5d4215011dea8f8cb08d7b 100644 (file)
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -569,7 +569,8 @@ 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);
@@ -667,7 +668,8 @@ 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)
 {
 }