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selinux: never allow relabeling on context mounts 

In the SECURITY_FS_USE_MNTPOINT case we never want to allow relabeling
files/directories, so we should never set the SBLABEL_MNT flag. The
'special handling' in selinux_is_sblabel_mnt() is only intended for when
the behavior is set to SECURITY_FS_USE_GENFS.

While there, make the logic in selinux_is_sblabel_mnt() more explicit
and add a BUILD_BUG_ON() to make sure that introducing a new
SECURITY_FS_USE_* forces a review of the logic.

Fixes: d5f3a5f6e7 ("selinux: add security in-core xattr support for pstore and debugfs")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Reviewed-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Ondrej Mosnacek 2018-12-21 21:18:52 +01:00 committed by Paul Moore
parent e46e01eebb
commit a83d6ddaeb
1 changed files with 31 additions and 9 deletions
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40
security/selinux/hooks.c
View File

@ -534,16 +534,10 @@ static int may_context_mount_inode_relabel(u32 sid,
return rc;
}
static int selinux_is_sblabel_mnt(struct super_block *sb)
static int selinux_is_genfs_special_handling(struct super_block *sb)
{
struct superblock_security_struct *sbsec = sb->s_security;
return sbsec->behavior == SECURITY_FS_USE_XATTR ||
sbsec->behavior == SECURITY_FS_USE_TRANS ||
sbsec->behavior == SECURITY_FS_USE_TASK ||
sbsec->behavior == SECURITY_FS_USE_NATIVE ||
/* Special handling. Genfs but also in-core setxattr handler */
!strcmp(sb->s_type->name, "sysfs") ||
/* Special handling. Genfs but also in-core setxattr handler */
return !strcmp(sb->s_type->name, "sysfs") ||
!strcmp(sb->s_type->name, "pstore") ||
!strcmp(sb->s_type->name, "debugfs") ||
!strcmp(sb->s_type->name, "tracefs") ||
@ -553,6 +547,34 @@ static int selinux_is_sblabel_mnt(struct super_block *sb)
!strcmp(sb->s_type->name, "cgroup2")));
}
static int selinux_is_sblabel_mnt(struct super_block *sb)
{
struct superblock_security_struct *sbsec = sb->s_security;
/*
* IMPORTANT: Double-check logic in this function when adding a new
* SECURITY_FS_USE_* definition!
*/
BUILD_BUG_ON(SECURITY_FS_USE_MAX != 7);
switch (sbsec->behavior) {
case SECURITY_FS_USE_XATTR:
case SECURITY_FS_USE_TRANS:
case SECURITY_FS_USE_TASK:
case SECURITY_FS_USE_NATIVE:
return 1;
case SECURITY_FS_USE_GENFS:
return selinux_is_genfs_special_handling(sb);
/* Never allow relabeling on context mounts */
case SECURITY_FS_USE_MNTPOINT:
case SECURITY_FS_USE_NONE:
default:
return 0;
}
}
static int sb_finish_set_opts(struct super_block *sb)
{
struct superblock_security_struct *sbsec = sb->s_security;