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security/selinux: allow security_sb_clone_mnt_opts to enable/disable native labeling behavior

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When an NFSv4 client performs a mount operation, it first mounts the
NFSv4 root and then does path walk to the exported path and performs a
submount on that, cloning the security mount options from the root's
superblock to the submount's superblock in the process.

Unless the NFS server has an explicit fsid=0 export with the
"security_label" option, the NFSv4 root superblock will not have
SBLABEL_MNT set, and neither will the submount superblock after cloning
the security mount options.  As a result, setxattr's of security labels
over NFSv4.2 will fail.  In a similar fashion, NFSv4.2 mounts mounted
with the context= mount option will not show the correct labels because
the nfs_server->caps flags of the cloned superblock will still have
NFS_CAP_SECURITY_LABEL set.

Allowing the NFSv4 client to enable or disable SECURITY_LSM_NATIVE_LABELS
behavior will ensure that the SBLABEL_MNT flag has the correct value
when the client traverses from an exported path without the
"security_label" option to one with the "security_label" option and
vice versa.  Similarly, checking to see if SECURITY_LSM_NATIVE_LABELS is
set upon return from security_sb_clone_mnt_opts() and clearing
NFS_CAP_SECURITY_LABEL if necessary will allow the correct labels to
be displayed for NFSv4.2 mounts mounted with the context= mount option.

Resolves: https://github.com/SELinuxProject/selinux-kernel/issues/35

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Tested-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Scott Mayhew 2017-06-05 11:45:04 -04:00 committed by Paul Moore
parent b4958c892e
commit 0b4d3452b8
5 changed files with 63 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
fs/nfs/super.c
View File

@ -2544,10 +2544,25 @@ EXPORT_SYMBOL_GPL(nfs_set_sb_security);
int nfs_clone_sb_security(struct super_block *s, struct dentry *mntroot,
struct nfs_mount_info *mount_info)
{
int error;
unsigned long kflags = 0, kflags_out = 0;
/* clone any lsm security options from the parent to the new sb */
if (d_inode(mntroot)->i_op != NFS_SB(s)->nfs_client->rpc_ops->dir_inode_ops)
return -ESTALE;
return security_sb_clone_mnt_opts(mount_info->cloned->sb, s);
if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL)
kflags |= SECURITY_LSM_NATIVE_LABELS;
error = security_sb_clone_mnt_opts(mount_info->cloned->sb, s, kflags,
&kflags_out);
if (error)
return error;
if (NFS_SB(s)->caps & NFS_CAP_SECURITY_LABEL &&
!(kflags_out & SECURITY_LSM_NATIVE_LABELS))
NFS_SB(s)->caps &= ~NFS_CAP_SECURITY_LABEL;
return 0;
}
EXPORT_SYMBOL_GPL(nfs_clone_sb_security);

4
include/linux/lsm_hooks.h
View File

@ -1409,7 +1409,9 @@ union security_list_options {
unsigned long kern_flags,
unsigned long *set_kern_flags);
int (*sb_clone_mnt_opts)(const struct super_block *oldsb,
struct super_block *newsb);
struct super_block *newsb,
unsigned long kern_flags,
unsigned long *set_kern_flags);
int (*sb_parse_opts_str)(char *options, struct security_mnt_opts *opts);
int (*dentry_init_security)(struct dentry *dentry, int mode,
const struct qstr *name, void **ctx,

8
include/linux/security.h
View File

@ -249,7 +249,9 @@ int security_sb_set_mnt_opts(struct super_block *sb,
unsigned long kern_flags,
unsigned long *set_kern_flags);
int security_sb_clone_mnt_opts(const struct super_block *oldsb,
struct super_block *newsb);
struct super_block *newsb,
unsigned long kern_flags,
unsigned long *set_kern_flags);
int security_sb_parse_opts_str(char *options, struct security_mnt_opts *opts);
int security_dentry_init_security(struct dentry *dentry, int mode,
const struct qstr *name, void **ctx,
@ -605,7 +607,9 @@ static inline int security_sb_set_mnt_opts(struct super_block *sb,
}
static inline int security_sb_clone_mnt_opts(const struct super_block *oldsb,
struct super_block *newsb)
struct super_block *newsb,
unsigned long kern_flags,
unsigned long *set_kern_flags)
{
return 0;
}

7
security/security.c
View File

@ -420,9 +420,12 @@ int security_sb_set_mnt_opts(struct super_block *sb,
EXPORT_SYMBOL(security_sb_set_mnt_opts);
int security_sb_clone_mnt_opts(const struct super_block *oldsb,
struct super_block *newsb)
struct super_block *newsb,
unsigned long kern_flags,
unsigned long *set_kern_flags)
{
return call_int_hook(sb_clone_mnt_opts, 0, oldsb, newsb);
return call_int_hook(sb_clone_mnt_opts, 0, oldsb, newsb,
kern_flags, set_kern_flags);
}
EXPORT_SYMBOL(security_sb_clone_mnt_opts);

35
security/selinux/hooks.c
View File

@ -525,8 +525,16 @@ static int sb_finish_set_opts(struct super_block *sb)
}
sbsec->flags |= SE_SBINITIALIZED;
/*
* Explicitly set or clear SBLABEL_MNT. It's not sufficient to simply
* leave the flag untouched because sb_clone_mnt_opts might be handing
* us a superblock that needs the flag to be cleared.
*/
if (selinux_is_sblabel_mnt(sb))
sbsec->flags |= SBLABEL_MNT;
else
sbsec->flags &= ~SBLABEL_MNT;
/* Initialize the root inode. */
rc = inode_doinit_with_dentry(root_inode, root);
@ -959,8 +967,11 @@ mismatch:
}
static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
struct super_block *newsb)
struct super_block *newsb,
unsigned long kern_flags,
unsigned long *set_kern_flags)
{
int rc = 0;
const struct superblock_security_struct *oldsbsec = oldsb->s_security;
struct superblock_security_struct *newsbsec = newsb->s_security;
@ -975,6 +986,13 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
if (!ss_initialized)
return 0;
/*
* Specifying internal flags without providing a place to
* place the results is not allowed.
*/
if (kern_flags && !set_kern_flags)
return -EINVAL;
/* how can we clone if the old one wasn't set up?? */
BUG_ON(!(oldsbsec->flags & SE_SBINITIALIZED));
@ -990,6 +1008,18 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
newsbsec->def_sid = oldsbsec->def_sid;
newsbsec->behavior = oldsbsec->behavior;
if (newsbsec->behavior == SECURITY_FS_USE_NATIVE &&
!(kern_flags & SECURITY_LSM_NATIVE_LABELS) && !set_context) {
rc = security_fs_use(newsb);
if (rc)
goto out;
}
if (kern_flags & SECURITY_LSM_NATIVE_LABELS && !set_context) {
newsbsec->behavior = SECURITY_FS_USE_NATIVE;
*set_kern_flags |= SECURITY_LSM_NATIVE_LABELS;
}
if (set_context) {
u32 sid = oldsbsec->mntpoint_sid;
@ -1009,8 +1039,9 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
}
sb_finish_set_opts(newsb);
out:
mutex_unlock(&newsbsec->lock);
return 0;
return rc;
}
static int selinux_parse_opts_str(char *options,