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fix setuid sometimes wouldn't

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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: Hugh Dickins <hugh@veritas.com>
Cc: stable@kernel.org
___

 fs/proc/base.c |   50 +++++++++++++++--------------------------------
 1 file changed, 16 insertions(+), 34 deletions(-)
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2009-03-28 23:21:27 +00:00 committed by Linus Torvalds
parent e426b64c41
commit 7c2c7d9930
1 changed files with 16 additions and 34 deletions
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50
fs/proc/base.c
View file

@ -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)