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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 [1]
Fixes: bd303368b7 ("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>
This commit is contained in:
Christian Brauner 2022-04-19 15:14:23 +02:00 committed by Linus Torvalds
parent b2d229d4dd
commit 705191b03d
3 changed files with 18 additions and 2 deletions
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10
fs/posix_acl.c
View File

@ -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,

6
fs/xattr.c
View File

@ -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) {

4
include/linux/posix_acl_xattr.h
View File

@ -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)
{
}