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selinux: try security xattr after genfs for kernfs filesystems

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Since kernfs supports the security xattr handlers, we can simply use
these to determine the inode's context, dropping the need to update it
from kernfs explicitly using a security_inode_notifysecctx() call.

We achieve this by setting a new sbsec flag SE_SBGENFS_XATTR to all
mounts that are known to use kernfs under the hood and then fetching the
xattrs after determining the fallback genfs sid in
inode_doinit_with_dentry() when this flag is set.

This will allow implementing full security xattr support in kernfs and
removing the ...notifysecctx() call in a subsequent patch.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: more manual merge fixups]
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Ondrej Mosnacek 2019-02-22 15:57:14 +01:00 committed by Paul Moore
parent d0c9c153b4
commit b754026bd9
2 changed files with 85 additions and 73 deletions
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157
security/selinux/hooks.c
View File

@ -751,11 +751,13 @@ static int selinux_set_mnt_opts(struct super_block *sb,
if (!strcmp(sb->s_type->name, "debugfs") ||
!strcmp(sb->s_type->name, "tracefs") ||
!strcmp(sb->s_type->name, "sysfs") ||
!strcmp(sb->s_type->name, "pstore") ||
!strcmp(sb->s_type->name, "pstore"))
sbsec->flags |= SE_SBGENFS;
if (!strcmp(sb->s_type->name, "sysfs") ||
!strcmp(sb->s_type->name, "cgroup") ||
!strcmp(sb->s_type->name, "cgroup2"))
sbsec->flags |= SE_SBGENFS;
sbsec->flags |= SE_SBGENFS | SE_SBGENFS_XATTR;
if (!sbsec->behavior) {
/*
@ -1354,6 +1356,67 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
return rc;
}
static int inode_doinit_use_xattr(struct inode *inode, struct dentry *dentry,
u32 def_sid, u32 *sid)
{
#define INITCONTEXTLEN 255
char *context;
unsigned int len;
int rc;
len = INITCONTEXTLEN;
context = kmalloc(len + 1, GFP_NOFS);
if (!context)
return -ENOMEM;
context[len] = '\0';
rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
if (rc == -ERANGE) {
kfree(context);
/* Need a larger buffer. Query for the right size. */
rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, NULL, 0);
if (rc < 0)
return rc;
len = rc;
context = kmalloc(len + 1, GFP_NOFS);
if (!context)
return -ENOMEM;
context[len] = '\0';
rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX,
context, len);
}
if (rc < 0) {
kfree(context);
if (rc != -ENODATA) {
pr_warn("SELinux: %s: getxattr returned %d for dev=%s ino=%ld\n",
__func__, -rc, inode->i_sb->s_id, inode->i_ino);
return rc;
}
*sid = def_sid;
return 0;
}
rc = security_context_to_sid_default(&selinux_state, context, rc, sid,
def_sid, GFP_NOFS);
if (rc) {
char *dev = inode->i_sb->s_id;
unsigned long ino = inode->i_ino;
if (rc == -EINVAL) {
pr_notice_ratelimited("SELinux: inode=%lu on dev=%s was found to have an invalid context=%s. This indicates you may need to relabel the inode or the filesystem in question.\n",
ino, dev, context);
} else {
pr_warn("SELinux: %s: context_to_sid(%s) returned %d for dev=%s ino=%ld\n",
__func__, context, -rc, dev, ino);
}
}
kfree(context);
return 0;
}
/* The inode's security attributes must be initialized before first use. */
static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dentry)
{
@ -1362,9 +1425,6 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
u32 task_sid, sid = 0;
u16 sclass;
struct dentry *dentry;
#define INITCONTEXTLEN 255
char *context = NULL;
unsigned len = 0;
int rc = 0;
if (isec->initialized == LABEL_INITIALIZED)
@ -1432,72 +1492,11 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
goto out;
}
len = INITCONTEXTLEN;
context = kmalloc(len+1, GFP_NOFS);
if (!context) {
rc = -ENOMEM;
dput(dentry);
goto out;
}
context[len] = '\0';
rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
if (rc == -ERANGE) {
kfree(context);
/* Need a larger buffer. Query for the right size. */
rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, NULL, 0);
if (rc < 0) {
dput(dentry);
goto out;
}
len = rc;
context = kmalloc(len+1, GFP_NOFS);
if (!context) {
rc = -ENOMEM;
dput(dentry);
goto out;
}
context[len] = '\0';
rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
}
rc = inode_doinit_use_xattr(inode, dentry, sbsec->def_sid,
&sid);
dput(dentry);
if (rc < 0) {
if (rc != -ENODATA) {
pr_warn("SELinux: %s: getxattr returned "
"%d for dev=%s ino=%ld\n", __func__,
-rc, inode->i_sb->s_id, inode->i_ino);
kfree(context);
goto out;
}
/* Map ENODATA to the default file SID */
sid = sbsec->def_sid;
rc = 0;
} else {
rc = security_context_to_sid_default(&selinux_state,
context, rc, &sid,
sbsec->def_sid,
GFP_NOFS);
if (rc) {
char *dev = inode->i_sb->s_id;
unsigned long ino = inode->i_ino;
if (rc == -EINVAL) {
if (printk_ratelimit())
pr_notice("SELinux: inode=%lu on dev=%s was found to have an invalid "
"context=%s. This indicates you may need to relabel the inode or the "
"filesystem in question.\n", ino, dev, context);
} else {
pr_warn("SELinux: %s: context_to_sid(%s) "
"returned %d for dev=%s ino=%ld\n",
__func__, context, -rc, dev, ino);
}
kfree(context);
/* Leave with the unlabeled SID */
rc = 0;
break;
}
}
kfree(context);
if (rc)
goto out;
break;
case SECURITY_FS_USE_TASK:
sid = task_sid;
@ -1548,9 +1547,21 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
goto out;
rc = selinux_genfs_get_sid(dentry, sclass,
sbsec->flags, &sid);
dput(dentry);
if (rc)
if (rc) {
dput(dentry);
goto out;
}
if ((sbsec->flags & SE_SBGENFS_XATTR) &&
(inode->i_opflags & IOP_XATTR)) {
rc = inode_doinit_use_xattr(inode, dentry,
sid, &sid);
if (rc) {
dput(dentry);
goto out;
}
}
dput(dentry);
}
break;
}

1
security/selinux/include/security.h
View File

@ -58,6 +58,7 @@
#define SE_SBINITIALIZED 0x0100
#define SE_SBPROC 0x0200
#define SE_SBGENFS 0x0400
#define SE_SBGENFS_XATTR 0x0800
#define CONTEXT_STR "context"
#define FSCONTEXT_STR "fscontext"