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lsm,selinux: add new hook to compare new mount to an existing mount

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Add a new hook that takes an existing super block and a new mount
with new options and determines if new options confict with an
existing mount or not.

A filesystem can use this new hook to determine if it can share
the an existing superblock with a new superblock for the new mount.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
Acked-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
[PM: tweak the subject line, fix tab/space problems]
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Olga Kornievskaia 2021-02-26 22:37:55 -05:00 committed by Paul Moore
parent 431c3be16b
commit 69c4a42d72
5 changed files with 78 additions and 0 deletions
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1
include/linux/lsm_hook_defs.h
View File

@ -62,6 +62,7 @@ LSM_HOOK(int, 0, sb_alloc_security, struct super_block *sb)
LSM_HOOK(void, LSM_RET_VOID, sb_free_security, struct super_block *sb)
LSM_HOOK(void, LSM_RET_VOID, sb_free_mnt_opts, void *mnt_opts)
LSM_HOOK(int, 0, sb_eat_lsm_opts, char *orig, void **mnt_opts)
LSM_HOOK(int, 0, sb_mnt_opts_compat, struct super_block *sb, void *mnt_opts)
LSM_HOOK(int, 0, sb_remount, struct super_block *sb, void *mnt_opts)
LSM_HOOK(int, 0, sb_kern_mount, struct super_block *sb)
LSM_HOOK(int, 0, sb_show_options, struct seq_file *m, struct super_block *sb)

6
include/linux/lsm_hooks.h
View File

@ -142,6 +142,12 @@
* @orig the original mount data copied from userspace.
* @copy copied data which will be passed to the security module.
* Returns 0 if the copy was successful.
* @sb_mnt_opts_compat:
* Determine if the new mount options in @mnt_opts are allowed given
* the existing mounted filesystem at @sb.
* @sb superblock being compared
* @mnt_opts new mount options
* Return 0 if options are compatible.
* @sb_remount:
* Extracts security system specific mount options and verifies no changes
* are being made to those options.

8
include/linux/security.h
View File

@ -294,6 +294,7 @@ int security_sb_alloc(struct super_block *sb);
void security_sb_free(struct super_block *sb);
void security_free_mnt_opts(void **mnt_opts);
int security_sb_eat_lsm_opts(char *options, void **mnt_opts);
int security_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts);
int security_sb_remount(struct super_block *sb, void *mnt_opts);
int security_sb_kern_mount(struct super_block *sb);
int security_sb_show_options(struct seq_file *m, struct super_block *sb);
@ -646,6 +647,13 @@ static inline int security_sb_remount(struct super_block *sb,
return 0;
}
static inline int security_sb_mnt_opts_compat(struct super_block *sb,
void *mnt_opts)
{
return 0;
}
static inline int security_sb_kern_mount(struct super_block *sb)
{
return 0;

7
security/security.c
View File

@ -890,6 +890,13 @@ int security_sb_eat_lsm_opts(char *options, void **mnt_opts)
}
EXPORT_SYMBOL(security_sb_eat_lsm_opts);
int security_sb_mnt_opts_compat(struct super_block *sb,
void *mnt_opts)
{
return call_int_hook(sb_mnt_opts_compat, 0, sb, mnt_opts);
}
EXPORT_SYMBOL(security_sb_mnt_opts_compat);
int security_sb_remount(struct super_block *sb,
void *mnt_opts)
{

56
security/selinux/hooks.c
View File

@ -2685,6 +2685,61 @@ free_opt:
return rc;
}
static int selinux_sb_mnt_opts_compat(struct super_block *sb, void *mnt_opts)
{
struct selinux_mnt_opts *opts = mnt_opts;
struct superblock_security_struct *sbsec = sb->s_security;
u32 sid;
int rc;
/*
* Superblock not initialized (i.e. no options) - reject if any
* options specified, otherwise accept.
*/
if (!(sbsec->flags & SE_SBINITIALIZED))
return opts ? 1 : 0;
/*
* Superblock initialized and no options specified - reject if
* superblock has any options set, otherwise accept.
*/
if (!opts)
return (sbsec->flags & SE_MNTMASK) ? 1 : 0;
if (opts->fscontext) {
rc = parse_sid(sb, opts->fscontext, &sid);
if (rc)
return 1;
if (bad_option(sbsec, FSCONTEXT_MNT, sbsec->sid, sid))
return 1;
}
if (opts->context) {
rc = parse_sid(sb, opts->context, &sid);
if (rc)
return 1;
if (bad_option(sbsec, CONTEXT_MNT, sbsec->mntpoint_sid, sid))
return 1;
}
if (opts->rootcontext) {
struct inode_security_struct *root_isec;
root_isec = backing_inode_security(sb->s_root);
rc = parse_sid(sb, opts->rootcontext, &sid);
if (rc)
return 1;
if (bad_option(sbsec, ROOTCONTEXT_MNT, root_isec->sid, sid))
return 1;
}
if (opts->defcontext) {
rc = parse_sid(sb, opts->defcontext, &sid);
if (rc)
return 1;
if (bad_option(sbsec, DEFCONTEXT_MNT, sbsec->def_sid, sid))
return 1;
}
return 0;
}
static int selinux_sb_remount(struct super_block *sb, void *mnt_opts)
{
struct selinux_mnt_opts *opts = mnt_opts;
@ -7078,6 +7133,7 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
LSM_HOOK_INIT(sb_free_mnt_opts, selinux_free_mnt_opts),
LSM_HOOK_INIT(sb_mnt_opts_compat, selinux_sb_mnt_opts_compat),
LSM_HOOK_INIT(sb_remount, selinux_sb_remount),
LSM_HOOK_INIT(sb_kern_mount, selinux_sb_kern_mount),
LSM_HOOK_INIT(sb_show_options, selinux_sb_show_options),