From 3a28cff3bd4bf43f02be0c4e7933aebf3dc8197e Mon Sep 17 00:00:00 2001 From: Stephen Smalley Date: Wed, 12 Dec 2018 10:10:55 -0500 Subject: selinux: avoid silent denials in permissive mode under RCU walk commit 0dc1ba24f7fff6 ("SELINUX: Make selinux cache VFS RCU walks safe") results in no audit messages at all if in permissive mode because the cache is updated during the rcu walk and thus no denial occurs on the subsequent ref walk. Fix this by not updating the cache when performing a non-blocking permission check. This only affects search and symlink read checks during rcu walk. Fixes: 0dc1ba24f7fff6 ("SELINUX: Make selinux cache VFS RCU walks safe") Reported-by: BMK Signed-off-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/hooks.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'security/selinux/hooks.c') diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index f0e36c3492ba..7f6068489a02 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2982,7 +2982,9 @@ static int selinux_inode_permission(struct inode *inode, int mask) return PTR_ERR(isec); rc = avc_has_perm_noaudit(&selinux_state, - sid, isec->sid, isec->sclass, perms, 0, &avd); + sid, isec->sid, isec->sclass, perms, + (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0, + &avd); audited = avc_audit_required(perms, &avd, rc, from_access ? FILE__AUDIT_ACCESS : 0, &denied); -- cgit v1.2.3 From e46e01eebbbcf2ff6d28ee7cae9f117e9d1572c8 Mon Sep 17 00:00:00 2001 From: Stephen Smalley Date: Wed, 12 Dec 2018 10:10:56 -0500 Subject: selinux: stop passing MAY_NOT_BLOCK to the AVC upon follow_link commit bda0be7ad9948 ("security: make inode_follow_link RCU-walk aware") switched selinux_inode_follow_link() to use avc_has_perm_flags() and pass down the MAY_NOT_BLOCK flag if called during RCU walk. However, the only test of MAY_NOT_BLOCK occurs during slow_avc_audit() and only if passing an inode as audit data (LSM_AUDIT_DATA_INODE). Since selinux_inode_follow_link() passes a dentry directly, passing MAY_NOT_BLOCK here serves no purpose. Switch selinux_inode_follow_link() to use avc_has_perm() and drop avc_has_perm_flags() since there are no other users. Signed-off-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/avc.c | 24 ++---------------------- security/selinux/hooks.c | 5 ++--- security/selinux/include/avc.h | 5 ----- 3 files changed, 4 insertions(+), 30 deletions(-) (limited to 'security/selinux/hooks.c') diff --git a/security/selinux/avc.c b/security/selinux/avc.c index 5de18a6d5c3f..9b63d8ee1687 100644 --- a/security/selinux/avc.c +++ b/security/selinux/avc.c @@ -867,9 +867,8 @@ static int avc_update_node(struct selinux_avc *avc, * permissive mode that only appear when in enforcing mode. * * See the corresponding handling in slow_avc_audit(), and the - * logic in selinux_inode_follow_link and selinux_inode_permission - * for the VFS MAY_NOT_BLOCK flag, which is transliterated into - * AVC_NONBLOCKING for avc_has_perm_noaudit(). + * logic in selinux_inode_permission for the MAY_NOT_BLOCK flag, + * which is transliterated into AVC_NONBLOCKING. */ if (flags & AVC_NONBLOCKING) return 0; @@ -1209,25 +1208,6 @@ int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass, return rc; } -int avc_has_perm_flags(struct selinux_state *state, - u32 ssid, u32 tsid, u16 tclass, u32 requested, - struct common_audit_data *auditdata, - int flags) -{ - struct av_decision avd; - int rc, rc2; - - rc = avc_has_perm_noaudit(state, ssid, tsid, tclass, requested, - (flags & MAY_NOT_BLOCK) ? AVC_NONBLOCKING : 0, - &avd); - - rc2 = avc_audit(state, ssid, tsid, tclass, requested, &avd, rc, - auditdata, flags); - if (rc2) - return rc2; - return rc; -} - u32 avc_policy_seqno(struct selinux_state *state) { return state->avc->avc_cache.latest_notif; diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 7f6068489a02..f08a0f201967 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2925,9 +2925,8 @@ static int selinux_inode_follow_link(struct dentry *dentry, struct inode *inode, if (IS_ERR(isec)) return PTR_ERR(isec); - return avc_has_perm_flags(&selinux_state, - sid, isec->sid, isec->sclass, FILE__READ, &ad, - rcu ? MAY_NOT_BLOCK : 0); + return avc_has_perm(&selinux_state, + sid, isec->sid, isec->sclass, FILE__READ, &ad); } static noinline int audit_inode_permission(struct inode *inode, diff --git a/security/selinux/include/avc.h b/security/selinux/include/avc.h index 74ea50977c20..7be0e1e90e8b 100644 --- a/security/selinux/include/avc.h +++ b/security/selinux/include/avc.h @@ -153,11 +153,6 @@ int avc_has_perm(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass, u32 requested, struct common_audit_data *auditdata); -int avc_has_perm_flags(struct selinux_state *state, - u32 ssid, u32 tsid, - u16 tclass, u32 requested, - struct common_audit_data *auditdata, - int flags); int avc_has_extended_perms(struct selinux_state *state, u32 ssid, u32 tsid, u16 tclass, u32 requested, -- cgit v1.2.3 From a83d6ddaebe541570291205cb538e35ad4ff94f9 Mon Sep 17 00:00:00 2001 From: Ondrej Mosnacek Date: Fri, 21 Dec 2018 21:18:52 +0100 Subject: 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: d5f3a5f6e7e7 ("selinux: add security in-core xattr support for pstore and debugfs") Signed-off-by: Ondrej Mosnacek Reviewed-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/hooks.c | 40 +++++++++++++++++++++++++++++++--------- 1 file changed, 31 insertions(+), 9 deletions(-) (limited to 'security/selinux/hooks.c') diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index f08a0f201967..f8931c5d252a 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -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; -- cgit v1.2.3 From 53e0c2aa9a59a48e3798ef193d573ade85aa80f5 Mon Sep 17 00:00:00 2001 From: Ondrej Mosnacek Date: Fri, 21 Dec 2018 21:18:53 +0100 Subject: selinux: do not override context on context mounts Ignore all selinux_inode_notifysecctx() calls on mounts with SBLABEL_MNT flag unset. This is achived by returning -EOPNOTSUPP for this case in selinux_inode_setsecurtity() (because that function should not be called in such case anyway) and translating this error to 0 in selinux_inode_notifysecctx(). This fixes behavior of kernfs-based filesystems when mounted with the 'context=' option. Before this patch, if a node's context had been explicitly set to a non-default value and later the filesystem has been remounted with the 'context=' option, then this node would show up as having the manually-set context and not the mount-specified one. Steps to reproduce: # mount -t cgroup2 cgroup2 /sys/fs/cgroup/unified # chcon unconfined_u:object_r:user_home_t:s0 /sys/fs/cgroup/unified/cgroup.stat # ls -lZ /sys/fs/cgroup/unified total 0 -r--r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Dec 13 10:41 cgroup.controllers -rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Dec 13 10:41 cgroup.max.depth -rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Dec 13 10:41 cgroup.max.descendants -rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Dec 13 10:41 cgroup.procs -r--r--r--. 1 root root unconfined_u:object_r:user_home_t:s0 0 Dec 13 10:41 cgroup.stat -rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Dec 13 10:41 cgroup.subtree_control -rw-r--r--. 1 root root system_u:object_r:cgroup_t:s0 0 Dec 13 10:41 cgroup.threads # umount /sys/fs/cgroup/unified # mount -o context=system_u:object_r:tmpfs_t:s0 -t cgroup2 cgroup2 /sys/fs/cgroup/unified Result before: # ls -lZ /sys/fs/cgroup/unified total 0 -r--r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.controllers -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.max.depth -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.max.descendants -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.procs -r--r--r--. 1 root root unconfined_u:object_r:user_home_t:s0 0 Dec 13 10:41 cgroup.stat -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.subtree_control -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.threads Result after: # ls -lZ /sys/fs/cgroup/unified total 0 -r--r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.controllers -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.max.depth -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.max.descendants -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.procs -r--r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.stat -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.subtree_control -rw-r--r--. 1 root root system_u:object_r:tmpfs_t:s0 0 Dec 13 10:41 cgroup.threads Signed-off-by: Ondrej Mosnacek Reviewed-by: Stephen Smalley Signed-off-by: Paul Moore --- security/selinux/hooks.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'security/selinux/hooks.c') diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index f8931c5d252a..81e012c66d95 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -3264,12 +3264,16 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags) { struct inode_security_struct *isec = inode_security_novalidate(inode); + struct superblock_security_struct *sbsec = inode->i_sb->s_security; u32 newsid; int rc; if (strcmp(name, XATTR_SELINUX_SUFFIX)) return -EOPNOTSUPP; + if (!(sbsec->flags & SBLABEL_MNT)) + return -EOPNOTSUPP; + if (!value || !size) return -EACCES; @@ -6415,7 +6419,10 @@ static void selinux_inode_invalidate_secctx(struct inode *inode) */ static int selinux_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen) { - return selinux_inode_setsecurity(inode, XATTR_SELINUX_SUFFIX, ctx, ctxlen, 0); + int rc = selinux_inode_setsecurity(inode, XATTR_SELINUX_SUFFIX, + ctx, ctxlen, 0); + /* Do not return error when suppressing label (SBLABEL_MNT not set). */ + return rc == -EOPNOTSUPP ? 0 : rc; } /* -- cgit v1.2.3