From e76227950e70ac5f97fe6e7c21f8152a0f924087 Mon Sep 17 00:00:00 2001 From: Tom Marshall Date: Wed, 25 Jan 2017 18:01:03 +0100 Subject: [PATCH] kernel: Only expose su when daemon is running It has been claimed that the PG implementation of 'su' has security vulnerabilities even when disabled. Unfortunately, the people that find these vulnerabilities often like to keep them private so they can profit from exploits while leaving users exposed to malicious hackers. In order to reduce the attack surface for vulnerabilites, it is therefore necessary to make 'su' completely inaccessible when it is not in use (except by the root and system users). Change-Id: I79716c72f74d0b7af34ec3a8054896c6559a181d --- fs/exec.c | 5 +++++ fs/namei.c | 9 +++++++++ fs/readdir.c | 15 +++++++++++++++ include/linux/dcache.h | 6 ++++++ include/linux/fs.h | 1 + include/linux/sched.h | 8 ++++++++ include/linux/uidgid.h | 1 + kernel/exit.c | 4 ++++ kernel/fork.c | 2 ++ kernel/sched/core.c | 32 ++++++++++++++++++++++++++++++++ 10 files changed, 83 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index 0428c34d4773..9497f4430c5e 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1636,6 +1636,11 @@ static int do_execveat_common(int fd, struct filename *filename, if (retval < 0) goto out; + if (d_is_su(file->f_path.dentry) && capable(CAP_SYS_ADMIN)) { + current->flags |= PF_SU; + su_exec(); + } + /* execve succeeded */ current->fs->in_exec = 0; current->in_execve = 0; diff --git a/fs/namei.c b/fs/namei.c index ea6050b6134a..94e792fa5e6b 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2164,6 +2164,15 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path if (!err && nd->flags & LOOKUP_DIRECTORY) if (!d_can_lookup(nd->path.dentry)) err = -ENOTDIR; + + if (!err) { + struct super_block *sb = nd->inode->i_sb; + if (sb->s_flags & MS_RDONLY) { + if (d_is_su(nd->path.dentry) && !su_visible()) + err = -ENOENT; + } + } + if (!err) { *path = nd->path; nd->path.mnt = NULL; diff --git a/fs/readdir.c b/fs/readdir.c index ced679179cac..91918f79e1db 100644 --- a/fs/readdir.c +++ b/fs/readdir.c @@ -39,6 +39,7 @@ int iterate_dir(struct file *file, struct dir_context *ctx) res = -ENOENT; if (!IS_DEADDIR(inode)) { ctx->pos = file->f_pos; + ctx->romnt = (inode->i_sb->s_flags & MS_RDONLY); res = file->f_op->iterate(file, ctx); file->f_pos = ctx->pos; fsnotify_access(file); @@ -50,6 +51,14 @@ out: } EXPORT_SYMBOL(iterate_dir); +static bool hide_name(const char *name, int namlen) +{ + if (namlen == 2 && !memcmp(name, "su", 2)) + if (!su_visible()) + return true; + return false; +} + /* * Traditional linux readdir() handling.. * @@ -89,6 +98,8 @@ static int fillonedir(struct dir_context *ctx, const char *name, int namlen, buf->result = -EOVERFLOW; return -EOVERFLOW; } + if (hide_name(name, namlen) && buf->ctx.romnt) + return 0; buf->result++; dirent = buf->dirent; if (!access_ok(VERIFY_WRITE, dirent, @@ -167,6 +178,8 @@ static int filldir(struct dir_context *ctx, const char *name, int namlen, buf->error = -EOVERFLOW; return -EOVERFLOW; } + if (hide_name(name, namlen) && buf->ctx.romnt) + return 0; dirent = buf->previous; if (dirent) { if (__put_user(offset, &dirent->d_off)) @@ -246,6 +259,8 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen, buf->error = -EINVAL; /* only used if we fail.. */ if (reclen > buf->count) return -EINVAL; + if (hide_name(name, namlen) && buf->ctx.romnt) + return 0; dirent = buf->previous; if (dirent) { if (__put_user(offset, &dirent->d_off)) diff --git a/include/linux/dcache.h b/include/linux/dcache.h index c066f6b56e58..d57e8a6c2f2c 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -522,6 +522,12 @@ static inline bool d_is_fallthru(const struct dentry *dentry) return dentry->d_flags & DCACHE_FALLTHRU; } +static inline bool d_is_su(const struct dentry *dentry) +{ + return dentry && + dentry->d_name.len == 2 && + !memcmp(dentry->d_name.name, "su", 2); +} extern int sysctl_vfs_cache_pressure; diff --git a/include/linux/fs.h b/include/linux/fs.h index f5f4e7871865..dd5d9a2b74a8 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1653,6 +1653,7 @@ typedef int (*filldir_t)(struct dir_context *, const char *, int, loff_t, u64, struct dir_context { const filldir_t actor; loff_t pos; + bool romnt; }; struct block_device_operations; diff --git a/include/linux/sched.h b/include/linux/sched.h index 8ea2ea1061ef..52c2aa842022 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -63,6 +63,12 @@ struct sched_param { #include +int su_instances(void); +bool su_running(void); +bool su_visible(void); +void su_exec(void); +void su_exit(void); + #define SCHED_ATTR_SIZE_VER0 48 /* sizeof first published struct */ /* @@ -2412,6 +2418,8 @@ extern void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, #define PF_FREEZER_SKIP 0x40000000 /* Freezer should not count it as freezable */ #define PF_SUSPEND_TASK 0x80000000 /* this thread called freeze_processes and should not be frozen */ +#define PF_SU 0x10000000 /* task is su */ + /* * Only the _current_ task can read/write to tsk->flags, but other * tasks can access tsk->flags in readonly mode for example diff --git a/include/linux/uidgid.h b/include/linux/uidgid.h index 54d41acb6974..421978a56414 100644 --- a/include/linux/uidgid.h +++ b/include/linux/uidgid.h @@ -55,6 +55,7 @@ static inline gid_t __kgid_val(kgid_t gid) #define GLOBAL_ROOT_GID KGIDT_INIT(0) //huruihuan add for cgroup control #define GLOBAL_SYSTEM_UID KUIDT_INIT(1000) +#define GLOBAL_SYSTEM_GID KGIDT_INIT(1000) #define INVALID_UID KUIDT_INIT(-1) #define INVALID_GID KGIDT_INIT(-1) diff --git a/kernel/exit.c b/kernel/exit.c index fc82e495b729..27fd06ee2104 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -717,6 +717,10 @@ void do_exit(long code) sched_exit(tsk); schedtune_exit_task(tsk); + if (tsk->flags & PF_SU) { + su_exit(); + } + /* * tsk->flags are checked in the futex code to protect against * an exiting task cleaning up the robust pi futexes. diff --git a/kernel/fork.c b/kernel/fork.c index caa23ca489bb..f1a53fbe6f46 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -365,6 +365,8 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) err = kaiser_map_thread_stack(tsk->stack); if (err) goto free_stack; + + tsk->flags &= ~PF_SU; #ifdef CONFIG_SECCOMP /* * We must handle setting up seccomp filters once we're under diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 6a5671bdb792..d507932f3908 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -98,6 +98,38 @@ #define CREATE_TRACE_POINTS #include +static atomic_t __su_instances; + +int su_instances(void) +{ + return atomic_read(&__su_instances); +} + +bool su_running(void) +{ + return su_instances() > 0; +} + +bool su_visible(void) +{ + kuid_t uid = current_uid(); + if (su_running()) + return true; + if (uid_eq(uid, GLOBAL_ROOT_UID) || uid_eq(uid, GLOBAL_SYSTEM_UID)) + return true; + return false; +} + +void su_exec(void) +{ + atomic_inc(&__su_instances); +} + +void su_exit(void) +{ + atomic_dec(&__su_instances); +} + ATOMIC_NOTIFIER_HEAD(load_alert_notifier_head); DEFINE_MUTEX(sched_domains_mutex);