Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map_files/directory v6

[Cyrill Gorcunov]

On Wed, Sep 07, 2011 at 03:23:01PM +0400, Vasiliy Kulikov wrote:
> Hi,
> 
> On Wed, Sep 07, 2011 at 02:33 +0900, Tejun Heo wrote:
> > On Tue, Sep 06, 2011 at 09:29:52PM +0400, Vasiliy Kulikov wrote:
> > > I agree with you.  I don't think that showing system-global debug
> > > information to all users by default is the right thing.  But some people
> > > doesn't agree with this point of view:
> > > 
> > > http://thread.gmane.org/gmane.linux.kernel/1108378
> > 
> > Yeap, I know there are two sides of the discussion but if one takes
> > the position that hiding such global debug info is more harmful, it's
> > only crazier to hide such information from each individual users of
> > the said global facility.  So, let's just forget about information
> > leak via freeing or not freeing here.  It's the wrong battle field.
> 
> Andrew, are you OK with closing the hole with pid_no_revalidate()
> and 0600 /proc/slabinfo?  If so, I feel I have to start this discussion
> with people participating in the discussion above: Theodore, Dan, Linus, etc.
> 
> Thanks,

Since kernel.org is still down (and Andrew, I can't download -mm bundle
as well for this very reason), here is an updated version for review.
I've updated map_files_d_revalidate to include ptrace hook, and switched
to flex_array. So while there is uncertainty in would we use pid_no_revalidate
or we wouldn't (seems calling ptrace hook there instead would help) i remain
the get/setattr untouched for a while. Also I hope an updated changelog
would make it more clear why we need this feature.

> By Andrew Morton
>
> But do we *really* need to do it in two passes?  Avoiding the temporary
> storage would involve doing more work under mmap_sem, and a put_filp()
> under mmap_sem might be problematic.

I fear we still need to use two passes in proc_map_files_readdir, I found no way
to escape lockdep complains when doing all work in one pass with mmap_sem taken.
The /maps does the same thing -- ie it fills maps file with mmap_sem taken to produce
robust data. And I'm not really sure what you mean with problematic put_filp?

	Cyrill
---
fs, proc: Introduce the /proc/<pid>/map_files/ directory v10

From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>

This one behaves similarly to the /proc/<pid>/fd/ one - it contains symlinks
one for each mapping with file, the name of a symlink is "vma->vm_start-vma->vm_end",
the target is the file. Opening a symlink results in a file that point exactly
to the same inode as them vma's one.

For example the ls -l of some arbitrary /proc/<pid>/map_files/

 | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
 | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
 | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
 | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
 | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so

This *helps* checkpointing process in three ways:

1. When dumping a task mappings we do know exact file that is mapped by particular
   region. We do this by opening /proc/$pid/map_files/address symlink the way we do
   with file descriptors.

2. This also helps in determining which anonymous shared mappings are shared with
   each other by comparing the inodes of them.

3. When restoring a set of process in case two of them has a mapping shared, we map
   the memory by the 1st one and then open its /proc/$pid/map_files/address file and
   map it by the 2nd task.

Using /proc/$pid/maps for this is quite inconvenient since it brings repeatable
re-reading and reparsing for this text file which slows down restore procesure
significantly. Also as being pointed in (3) it is a way easier to use top level
shared mapping in children as /proc/$pid/map_files/address when needed.

v2: (spotted by Tejun Heo)
 - /proc/<pid>/mfd changed to /proc/<pid>/map_files
 - find_vma helper is used instead of linear search
 - routines are re-grouped
 - d_revalidate is set now

v3:
 - d_revalidate reworked, now it should drops no longer valid dentries (Tejun Heo)
 - ptrace_may_access added into proc_map_files_lookup (Vasiliy Kulikov)
 - because of filldir (which eventually might need to lock mmap_sem)
   the proc_map_files_readdir() was reworked to call proc_fill_cache()
   with unlocked mmap_sem

v4: (feedback by Tejun Heo and Vasiliy Kulikov)
 - instead of saving data in proc_inode we rather make a dentry name
   to keep both vm_start and vm_end accordingly
 - d_revalidate now honor task credentials

v5: (feedback by Kirill A. Shutemov)
 - don't forget to release mmap_sem on error path

v6:
 - sizeof get used in map_files_info which shrink member a bit on
   x86-32 (by Kirill A. Shutemov)
 - map_name_to_addr returns -EINVAL instead of -1
   which is more appropriate (by Tejun Heo)

v7:
 - add [get/set]attr handlers for
   proc_map_files_inode_operations (by Vasiliy Kulikov)

v8:
 - Kirill A. Shutemov spotted a parasite semicolon
   which ruined the ptrace_check call, fixed.

v9: (feedback by Andrew Morton)
 - find_exact_vma moved into include/linux/mm.h as an inline helper
 - proc_map_files_setattr uses either kmalloc or vmalloc depending
   on how many ojects are to be allocated
 - no more map_name_to_addr but dname_to_vma_addr introduced instead
   and it uses sscanf because in one case the find_exact_vma() is used
   only to confirm existence of vma area the boolean flag is used
 - fancy justification dropped
 - still the proc_map_files_get/setattr leaved untouched
   until additional fd/ patches applied first.

v10: (feedback by Andrew Morton)
 - flex_arrays are used instead of kmalloc/vmalloc calls
 - map_files_d_revalidate use ptrace_may_access for
   security reason (by Vasiliy Kulikov)

Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
CC: Tejun Heo <tj@xxxxxxxxxx>
CC: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
CC: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx>
CC: Alexey Dobriyan <adobriyan@xxxxxxxxx>
CC: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 fs/proc/base.c     |  366 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h |   12 +
 2 files changed, 378 insertions(+)

Index: linux-2.6.git/fs/proc/base.c
===================================================================
--- linux-2.6.git.orig/fs/proc/base.c
+++ linux-2.6.git/fs/proc/base.c
@@ -83,6 +83,7 @@
 #include <linux/pid_namespace.h>
 #include <linux/fs_struct.h>
 #include <linux/slab.h>
+#include <linux/flex_array.h>
 #ifdef CONFIG_HARDWALL
 #include <asm/hardwall.h>
 #endif
@@ -2171,6 +2172,370 @@ static const struct file_operations proc
 };
 
 /*
+ * dname_to_vma_addr - maps a dentry name into two unsigned longs
+ * which represent vma start and end addresses.
+ */
+static int dname_to_vma_addr(struct dentry *dentry,
+			     unsigned long *start, unsigned long *end)
+{
+	if (sscanf(dentry->d_name.name, "%lx-%lx", start, end) != 2)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int map_files_d_revalidate(struct dentry *dentry, struct nameidata *nd)
+{
+	unsigned long vm_start, vm_end;
+	bool exact_vma_exists = false;
+	struct task_struct *task;
+	const struct cred *cred;
+	struct mm_struct *mm;
+	struct inode *inode;
+
+	if (nd && nd->flags & LOOKUP_RCU)
+		return -ECHILD;
+
+	inode = dentry->d_inode;
+	task = get_proc_task(inode);
+	if (!task)
+		goto out;
+
+	if (!ptrace_may_access(task, PTRACE_MODE_READ))
+		goto out;
+
+	mm = get_task_mm(task);
+	put_task_struct(task);
+	if (!mm)
+		goto out;
+
+	if (!dname_to_vma_addr(dentry, &vm_start, &vm_end)) {
+		down_read(&mm->mmap_sem);
+		exact_vma_exists = !!find_exact_vma(mm, vm_start, vm_end);
+		up_read(&mm->mmap_sem);
+	}
+
+	mmput(mm);
+
+	if (exact_vma_exists) {
+		if (task_dumpable(task)) {
+			rcu_read_lock();
+			cred = __task_cred(task);
+			inode->i_uid = cred->euid;
+			inode->i_gid = cred->egid;
+			rcu_read_unlock();
+		} else {
+			inode->i_uid = 0;
+			inode->i_gid = 0;
+		}
+		security_task_to_inode(task, inode);
+		return 1;
+	}
+out:
+	d_drop(dentry);
+	return 0;
+}
+
+static const struct dentry_operations tid_map_files_dentry_operations = {
+	.d_revalidate	= map_files_d_revalidate,
+	.d_delete	= pid_delete_dentry,
+};
+
+static int proc_map_files_get_link(struct dentry *dentry, struct path *path)
+{
+	unsigned long vm_start, vm_end;
+	struct vm_area_struct *vma;
+	struct task_struct *task;
+	struct mm_struct *mm;
+	int rc = -ENOENT;
+
+	task = get_proc_task(dentry->d_inode);
+	if (!task)
+		goto out;
+
+	mm = get_task_mm(task);
+	put_task_struct(task);
+	if (!mm)
+		goto out;
+
+	rc = dname_to_vma_addr(dentry, &vm_start, &vm_end);
+	if (rc)
+		goto out_mmput;
+
+	down_read(&mm->mmap_sem);
+	vma = find_exact_vma(mm, vm_start, vm_end);
+	if (vma && vma->vm_file) {
+		*path = vma->vm_file->f_path;
+		path_get(path);
+		rc = 0;
+	}
+	up_read(&mm->mmap_sem);
+
+out_mmput:
+	mmput(mm);
+out:
+	return rc;
+}
+
+struct map_files_info {
+	struct file	*file;
+	unsigned long	len;
+	unsigned char	name[4*sizeof(long)+2]; /* max: %lx-%lx\0 */
+};
+
+static struct dentry *
+proc_map_files_instantiate(struct inode *dir, struct dentry *dentry,
+			   struct task_struct *task, const void *ptr)
+{
+	const struct file *file = ptr;
+	struct proc_inode *ei;
+	struct inode *inode;
+
+	if (!file)
+		return ERR_PTR(-ENOENT);
+
+	inode = proc_pid_make_inode(dir->i_sb, task);
+	if (!inode)
+		return ERR_PTR(-ENOENT);
+
+	ei = PROC_I(inode);
+	ei->op.proc_get_link = proc_map_files_get_link;
+
+	inode->i_op = &proc_pid_link_inode_operations;
+	inode->i_size = 64;
+	inode->i_mode = S_IFLNK;
+
+	if (file->f_mode & FMODE_READ)
+		inode->i_mode |= S_IRUSR | S_IXUSR;
+	if (file->f_mode & FMODE_WRITE)
+		inode->i_mode |= S_IWUSR | S_IXUSR;
+
+	d_set_d_op(dentry, &tid_map_files_dentry_operations);
+	d_add(dentry, inode);
+
+	return NULL;
+}
+
+static struct dentry *proc_map_files_lookup(struct inode *dir,
+		struct dentry *dentry, struct nameidata *nd)
+{
+	unsigned long vm_start, vm_end;
+	struct task_struct *task;
+	struct vm_area_struct *vma;
+	struct mm_struct *mm;
+	struct dentry *result;
+
+	result = ERR_PTR(-ENOENT);
+	task = get_proc_task(dir);
+	if (!task)
+		goto out_no_task;
+
+	result = ERR_PTR(-EPERM);
+	if (!ptrace_may_access(task, PTRACE_MODE_READ))
+		goto out_no_mm;
+
+	result = ERR_PTR(-ENOENT);
+	if (dname_to_vma_addr(dentry, &vm_start, &vm_end))
+		goto out_no_mm;
+
+	mm = get_task_mm(task);
+	if (!mm)
+		goto out_no_mm;
+
+	down_read(&mm->mmap_sem);
+	vma = find_exact_vma(mm, vm_start, vm_end);
+	if (!vma)
+		goto out_no_vma;
+
+	result = proc_map_files_instantiate(dir, dentry, task, vma->vm_file);
+
+out_no_vma:
+	up_read(&mm->mmap_sem);
+	mmput(mm);
+out_no_mm:
+	put_task_struct(task);
+out_no_task:
+	return result;
+}
+
+static int proc_map_files_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	struct inode *inode = dentry->d_inode;
+	struct task_struct *task;
+	int ret = -EACCES;
+
+	task = get_proc_task(inode);
+	if (!task)
+		return -ESRCH;
+
+	if (!lock_trace(task)) {
+		ret = proc_setattr(dentry, attr);
+		unlock_trace(task);
+	}
+
+	put_task_struct(task);
+	return ret;
+}
+
+static int proc_map_files_getattr(struct vfsmount *mnt, struct dentry *dentry,
+				  struct kstat *stat)
+{
+	struct inode *inode = dentry->d_inode;
+	struct task_struct *task;
+	int ret = -EACCES;
+
+	task = get_proc_task(inode);
+	if (!task)
+		return -ESRCH;
+
+	if (!lock_trace(task)) {
+		generic_fillattr(inode, stat);
+		unlock_trace(task);
+		ret = 0;
+	}
+
+	put_task_struct(task);
+	return ret;
+}
+
+static const struct inode_operations proc_map_files_inode_operations = {
+	.lookup		= proc_map_files_lookup,
+	.setattr	= proc_map_files_setattr,
+	.getattr	= proc_map_files_getattr,
+};
+
+static int proc_map_files_readdir(struct file *filp, void *dirent, filldir_t filldir)
+{
+	struct dentry *dentry = filp->f_path.dentry;
+	struct inode *inode = dentry->d_inode;
+	struct vm_area_struct *vma;
+	struct task_struct *task;
+	struct mm_struct *mm;
+	ino_t ino;
+	int ret;
+
+	ret = -ENOENT;
+	task = get_proc_task(inode);
+	if (!task)
+		goto out_no_task;
+
+	ret = -EPERM;
+	if (!ptrace_may_access(task, PTRACE_MODE_READ))
+		goto out;
+
+	ret = 0;
+	switch (filp->f_pos) {
+	case 0:
+		ino = inode->i_ino;
+		if (filldir(dirent, ".", 1, 0, ino, DT_DIR) < 0)
+			goto out;
+		filp->f_pos++;
+	case 1:
+		ino = parent_ino(dentry);
+		if (filldir(dirent, "..", 2, 1, ino, DT_DIR) < 0)
+			goto out;
+		filp->f_pos++;
+	default:
+	{
+		unsigned long nr_files, used, pos, i;
+		struct flex_array *fa = NULL;
+		struct map_files_info info;
+		struct map_files_info *p;
+
+		mm = get_task_mm(task);
+		if (!mm)
+			goto out;
+		down_read(&mm->mmap_sem);
+
+		nr_files = 0;
+		used = 0;
+
+		/*
+		 * We need two passes here:
+		 *
+		 *  1) Collect vmas of mapped files with mmap_sem taken
+		 *  2) Release mmap_sem and instantiate entries
+		 *
+		 * otherwise we get lockdep complained, since filldir()
+		 * routine might require mmap_sem taken in might_fault().
+		 */
+
+		for (vma = mm->mmap; vma; vma = vma->vm_next) {
+			if (vma->vm_file)
+				nr_files++;
+		}
+
+		if (nr_files) {
+			ret = -ENOMEM;
+			fa = flex_array_alloc(sizeof(info), nr_files, GFP_KERNEL);
+			if (!fa)
+				goto err;
+			if (flex_array_prealloc(fa, 0, nr_files, GFP_KERNEL))
+				goto err;
+			for (vma = mm->mmap, pos = 2; vma; vma = vma->vm_next) {
+				if (!vma->vm_file)
+					continue;
+				if (++pos <= filp->f_pos)
+					continue;
+
+				get_file(vma->vm_file);
+				info.file = vma->vm_file;
+				info.len = snprintf(info.name, sizeof(info.name),
+						    "%lx-%lx", vma->vm_start,
+						    vma->vm_end);
+				if (flex_array_put(fa, used, &info, GFP_KERNEL)) {
+					/*
+					 * This must never happen on preallocated array,
+					 * but just to be sure.
+					 */
+					WARN_ON_ONCE(1);
+					put_filp(vma->vm_file);
+					goto err;
+				}
+				used++;
+			}
+			ret = 0;
+		}
+err:
+		up_read(&mm->mmap_sem);
+
+		for (i = 0; i < used && !ret; i++) {
+			p = flex_array_get(fa, i);
+			ret = proc_fill_cache(filp, dirent, filldir,
+					      p->name, p->len,
+					      proc_map_files_instantiate,
+					      task, p->file);
+			if (ret)
+				break;
+			filp->f_pos++;
+			put_filp(p->file);
+		}
+
+		for (; i < used; i++) {
+			p = flex_array_get(fa, i);
+			put_filp(p->file);
+		}
+
+		if (fa)
+			flex_array_free(fa);
+
+		mmput(mm);
+	}
+	}
+
+out:
+	put_task_struct(task);
+out_no_task:
+	return ret;
+}
+
+static const struct file_operations proc_map_files_operations = {
+	.read		= generic_read_dir,
+	.readdir	= proc_map_files_readdir,
+	.llseek		= default_llseek,
+};
+
+/*
  * /proc/pid/fd needs a special permission handler so that a process can still
  * access /proc/self/fd after it has executed a setuid().
  */
@@ -2785,6 +3150,7 @@ static const struct inode_operations pro
 static const struct pid_entry tgid_base_stuff[] = {
 	DIR("task",       S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
 	DIR("fd",         S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
+	DIR("map_files",  S_IRUSR|S_IXUSR, proc_map_files_inode_operations, proc_map_files_operations),
 	DIR("fdinfo",     S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
 	DIR("ns",	  S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
 #ifdef CONFIG_NET
Index: linux-2.6.git/include/linux/mm.h
===================================================================
--- linux-2.6.git.orig/include/linux/mm.h
+++ linux-2.6.git/include/linux/mm.h
@@ -1491,6 +1491,18 @@ static inline unsigned long vma_pages(st
 	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
 }
 
+/* Look up the first VMA which exactly match the interval vm_start ... vm_end */
+static inline struct vm_area_struct *
+find_exact_vma(struct mm_struct *mm, unsigned long vm_start, unsigned long vm_end)
+{
+	struct vm_area_struct *vma = find_vma(mm, vm_start);
+
+	if (vma && (vma->vm_start != vm_start || vma->vm_end != vm_end))
+		vma = NULL;
+
+	return vma;
+}
+
 #ifdef CONFIG_MMU
 pgprot_t vm_get_page_prot(unsigned long vm_flags);
 #else
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/