diff options
author | Christian Brauner | 2022-08-29 14:38:43 +0200 |
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committer | Christian Brauner (Microsoft) | 2022-08-31 16:37:58 +0200 |
commit | 52edb4080eb9606536c34d5d642ccd9d35ad5d08 (patch) | |
tree | deb0a8a618fa6d40ff89201f5e223b43e5186d85 /security | |
parent | 6b70fe0601adb1396ad0b85cdf05d217500b49e7 (diff) |
acl: move idmapping handling into posix_acl_xattr_set()
The uapi POSIX ACL struct passed through the value argument during
setxattr() contains {g,u}id values encoded via ACL_{GROUP,USER} entries
that should actually be stored in the form of k{g,u}id_t (See [1] for a
long explanation of the issue.).
In 0c5fd887d2bb ("acl: move idmapped mount fixup into vfs_{g,s}etxattr()")
we took the mount's idmapping into account in order to let overlayfs
handle POSIX ACLs on idmapped layers correctly. The fixup is currently
performed directly in vfs_setxattr() which piles on top of the earlier
hackiness by handling the mount's idmapping and stuff the vfs{g,u}id_t
values into the uapi struct as well. While that is all correct and works
fine it's just ugly.
Now that we have introduced vfs_make_posix_acl() earlier move handling
idmapped mounts out of vfs_setxattr() and into the POSIX ACL handler
where it belongs.
Note that we also need to call vfs_make_posix_acl() for EVM which
interpretes POSIX ACLs during security_inode_setxattr(). Leave them a
longer comment for future reference.
All filesystems that support idmapped mounts via FS_ALLOW_IDMAP use the
standard POSIX ACL xattr handlers and are covered by this change. This
includes overlayfs which simply calls vfs_{g,s}etxattr().
The following filesystems use custom POSIX ACL xattr handlers: 9p, cifs,
ecryptfs, and ntfs3 (and overlayfs but we've covered that in the paragraph
above) and none of them support idmapped mounts yet.
Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org/ [1]
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Reviewed-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
Diffstat (limited to 'security')
-rw-r--r-- | security/integrity/evm/evm_main.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 2e6fb6e2ffd2..23d484e05e6f 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -457,10 +457,21 @@ static int evm_xattr_acl_change(struct user_namespace *mnt_userns, int rc; /* - * user_ns is not relevant here, ACL_USER/ACL_GROUP don't have impact - * on the inode mode (see posix_acl_equiv_mode()). + * An earlier comment here mentioned that the idmappings for + * ACL_{GROUP,USER} don't matter since EVM is only interested in the + * mode stored as part of POSIX ACLs. Nonetheless, if it must translate + * from the uapi POSIX ACL representation to the VFS internal POSIX ACL + * representation it should do so correctly. There's no guarantee that + * we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters + * for the mode at some point and it's difficult to keep track of all + * the LSM and integrity modules and what they do to POSIX ACLs. + * + * Frankly, EVM shouldn't try to interpret the uapi struct for POSIX + * ACLs it received. It requires knowledge that only the VFS is + * guaranteed to have. */ - acl = posix_acl_from_xattr(&init_user_ns, xattr_value, xattr_value_len); + acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode), + xattr_value, xattr_value_len); if (IS_ERR_OR_NULL(acl)) return 1; |