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Commit 7c2c7d99 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

fix setuid sometimes wouldn't 



check_unsafe_exec() also notes whether the fs_struct is being
shared by more threads than will get killed by the exec, and if so
sets LSM_UNSAFE_SHARE to make bprm_set_creds() careful about euid.
But /proc/<pid>/cwd and /proc/<pid>/root lookups make transient
use of get_fs_struct(), which also raises that sharing count.

This might occasionally cause a setuid program not to change euid,
in the same way as happened with files->count (check_unsafe_exec
also looks at sighand->count, but /proc doesn't raise that one).

We'd prefer exec not to unshare fs_struct: so fix this in procfs,
replacing get_fs_struct() by get_fs_path(), which does path_get
while still holding task_lock, instead of raising fs->count.

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Cc: stable@kernel.org
___

 fs/proc/base.c |   50 +++++++++++++++--------------------------------
 1 file changed, 16 insertions(+), 34 deletions(-)
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e426b64c

fs/proc/base.c

+16 −34
Original line number Diff line number Diff line
@@ -146,15 +146,22 @@ static unsigned int pid_entry_count_dirs(const struct pid_entry *entries, 
	return count;

}



static struct fs_struct *get_fs_struct(struct task_struct *task)

static int get_fs_path(struct task_struct *task, struct path *path, bool root)

{

	struct fs_struct *fs;

	int result = -ENOENT;



	task_lock(task);

	fs = task->fs;

	if(fs)

		atomic_inc(&fs->count);

	if (fs) {

		read_lock(&fs->lock);

		*path = root ? fs->root : fs->pwd;

		path_get(path);

		read_unlock(&fs->lock);

		result = 0;

	}

	task_unlock(task);

	return fs;

	return result;

}



static int get_nr_threads(struct task_struct *tsk)
@@ -172,42 +179,24 @@ static int get_nr_threads(struct task_struct *tsk) 
static int proc_cwd_link(struct inode *inode, struct path *path)

{

	struct task_struct *task = get_proc_task(inode);

	struct fs_struct *fs = NULL;

	int result = -ENOENT;



	if (task) {

		fs = get_fs_struct(task);

		result = get_fs_path(task, path, 0);

		put_task_struct(task);

	}

	if (fs) {

		read_lock(&fs->lock);

		*path = fs->pwd;

		path_get(&fs->pwd);

		read_unlock(&fs->lock);

		result = 0;

		put_fs_struct(fs);

	}

	return result;

}



static int proc_root_link(struct inode *inode, struct path *path)

{

	struct task_struct *task = get_proc_task(inode);

	struct fs_struct *fs = NULL;

	int result = -ENOENT;



	if (task) {

		fs = get_fs_struct(task);

		result = get_fs_path(task, path, 1);

		put_task_struct(task);

	}

	if (fs) {

		read_lock(&fs->lock);

		*path = fs->root;

		path_get(&fs->root);

		read_unlock(&fs->lock);

		result = 0;

		put_fs_struct(fs);

	}

	return result;

}
@@ -596,7 +585,6 @@ static int mounts_open_common(struct inode *inode, struct file *file, 
	struct task_struct *task = get_proc_task(inode);

	struct nsproxy *nsp;

	struct mnt_namespace *ns = NULL;

	struct fs_struct *fs = NULL;

	struct path root;

	struct proc_mounts *p;

	int ret = -EINVAL;
@@ -610,22 +598,16 @@ static int mounts_open_common(struct inode *inode, struct file *file, 
				get_mnt_ns(ns);

		}

		rcu_read_unlock();

		if (ns)

			fs = get_fs_struct(task);

		if (ns && get_fs_path(task, &root, 1) == 0)

			ret = 0;

		put_task_struct(task);

	}



	if (!ns)

		goto err;

	if (!fs)

	if (ret)

		goto err_put_ns;



	read_lock(&fs->lock);

	root = fs->root;

	path_get(&root);

	read_unlock(&fs->lock);

	put_fs_struct(fs);



	ret = -ENOMEM;

	p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL);

	if (!p)