Re: d_path() and overlay fs

From: Miklos Szeredi
Date: Fri Mar 20 2015 - 12:01:37 EST

On Fri, Mar 20, 2015 at 09:41:25AM -0400, Josh Boyer wrote:
> On Fri, Mar 20, 2015 at 9:29 AM, Karel Zak <kzak@xxxxxxxxxx> wrote:
> >
> > Hi,
> >
> > kernel-4.0.0-0.rc4.git1.3.fc23 (I have nothing more recent right now,
> > sorry it the problem is already fixed).
>
> That equates to Linux v4.0-rc4-88-g7b09ac704bac upstream.
>
> Fedora has Linux v4.0-rc4-199-gb314acaccd7e queued to build today,
> which does include an overlayfs fix pull but I have no idea if it
> solves the issue.

It does not.

However the following patch should. It's not much tested and I understand that
it doesn't solve the whole problem that dhowells is working on (selinux in
particular)

But it does take care of the majority of f_path users that actually want the
covering path.

Comments, testing welcome.

Thanks,
Miklos

---
arch/arc/kernel/troubleshoot.c | 10 ++------
arch/blackfin/kernel/trace.c | 2 -
arch/tile/kernel/stack.c | 2 -
arch/tile/mm/elf.c | 2 -
drivers/block/loop.c | 2 -
drivers/md/bitmap.c | 4 +--
drivers/md/md.c | 2 -
drivers/usb/gadget/function/f_mass_storage.c | 2 -
drivers/usb/gadget/function/storage_common.c | 2 -
fs/binfmt_elf.c | 4 +--
fs/coredump.c | 2 -
fs/ext4/super.c | 2 -
fs/file_table.c | 1
fs/open.c | 32 +++++++++++++++++++++++----
fs/proc/base.c | 6 ++---
fs/proc/fd.c | 9 +++++--
fs/proc/nommu.c | 2 -
fs/proc/task_mmu.c | 4 +--
fs/proc/task_nommu.c | 2 -
fs/seq_file.c | 17 ++++++++++++++
include/linux/fs.h | 4 +++
include/linux/seq_file.h | 1
kernel/events/core.c | 2 -
mm/memory.c | 2 -
mm/swapfile.c | 2 -
25 files changed, 83 insertions(+), 37 deletions(-)

--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -219,6 +219,7 @@ static void __fput(struct file *file)
put_write_access(inode);
__mnt_drop_write(mnt);
}
+ path_put(&file->f_covering_path);
file->f_path.dentry = NULL;
file->f_path.mnt = NULL;
file->f_inode = NULL;
--- a/fs/open.c
+++ b/fs/open.c
@@ -849,6 +849,24 @@ struct file *dentry_open(const struct pa
}
EXPORT_SYMBOL(dentry_open);

+void f_covering_path(struct file *filp, struct path *path)
+{
+ if (filp->f_covering_path.dentry)
+ *path = filp->f_covering_path;
+ else
+ *path = filp->f_path;
+}
+EXPORT_SYMBOL(f_covering_path);
+
+char *file_path(struct file *filp, char *buf, int buflen)
+{
+ struct path path;
+
+ f_covering_path(filp, &path);
+ return d_path(&path, buf, buflen);
+}
+EXPORT_SYMBOL(file_path);
+
/**
* vfs_open - open the file at the given path
* @path: path to open
@@ -859,13 +877,19 @@ int vfs_open(const struct path *path, st
const struct cred *cred)
{
struct inode *inode = path->dentry->d_inode;
+ int err;

- if (inode->i_op->dentry_open)
- return inode->i_op->dentry_open(path->dentry, filp, cred);
- else {
+ if (inode->i_op->dentry_open) {
+ err = inode->i_op->dentry_open(path->dentry, filp, cred);
+ if (!err && filp->f_path.dentry != path->dentry) {
+ filp->f_covering_path = *path;
+ path_get(&filp->f_covering_path);
+ }
+ } else {
filp->f_path = *path;
- return do_dentry_open(filp, NULL, cred);
+ err = do_dentry_open(filp, NULL, cred);
}
+ return err;
}
EXPORT_SYMBOL(vfs_open);

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1363,8 +1363,8 @@ static int proc_exe_link(struct dentry *
exe_file = get_mm_exe_file(mm);
mmput(mm);
if (exe_file) {
- *exe_path = exe_file->f_path;
- path_get(&exe_file->f_path);
+ f_covering_path(exe_file, exe_path);
+ path_get(exe_path);
fput(exe_file);
return 0;
} else
@@ -1735,7 +1735,7 @@ static int proc_map_files_get_link(struc
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;
+ f_covering_path(vma->vm_file, path);
path_get(path);
rc = 0;
}
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -49,9 +49,12 @@ static int seq_show(struct seq_file *m,
}

if (!ret) {
+ struct path path;
+
+ f_covering_path(file, &path);
seq_printf(m, "pos:\t%lli\nflags:\t0%o\nmnt_id:\t%i\n",
(long long)file->f_pos, f_flags,
- real_mount(file->f_path.mnt)->mnt_id);
+ real_mount(path.mnt)->mnt_id);
if (file->f_op->show_fdinfo)
file->f_op->show_fdinfo(m, file);
ret = seq_has_overflowed(m);
@@ -157,8 +160,8 @@ static int proc_fd_link(struct dentry *d
spin_lock(&files->file_lock);
fd_file = fcheck_files(files, fd);
if (fd_file) {
- *path = fd_file->f_path;
- path_get(&fd_file->f_path);
+ f_covering_path(fd_file, path);
+ path_get(path);
ret = 0;
}
spin_unlock(&files->file_lock);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -833,6 +833,7 @@ struct file {
struct list_head f_tfile_llink;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
+ struct path f_covering_path;
} __attribute__((aligned(4))); /* lest something weird decides that 2 is OK */

struct file_handle {
@@ -2466,6 +2467,9 @@ extern struct file * open_exec(const cha
extern int is_subdir(struct dentry *, struct dentry *);
extern int path_is_under(struct path *, struct path *);

+extern char *file_path(struct file *, char *, int);
+extern void f_covering_path(struct file *, struct path *);
+
#include <linux/err.h>

/* needed for stackable file system support */
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -620,7 +620,7 @@ static ssize_t loop_attr_backing_file_sh

spin_lock_irq(&lo->lo_lock);
if (lo->lo_backing_file)
- p = d_path(&lo->lo_backing_file->f_path, buf, PAGE_SIZE - 1);
+ p = file_path(lo->lo_backing_file, buf, PAGE_SIZE - 1);
spin_unlock_irq(&lo->lo_lock);

if (IS_ERR_OR_NULL(p))
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -123,6 +123,7 @@ __printf(2, 3) int seq_printf(struct seq
__printf(2, 0) int seq_vprintf(struct seq_file *, const char *, va_list args);

int seq_path(struct seq_file *, const struct path *, const char *);
+int seq_file_path(struct seq_file *, struct file *, const char *);
int seq_dentry(struct seq_file *, struct dentry *, const char *);
int seq_path_root(struct seq_file *m, const struct path *path,
const struct path *root, const char *esc);
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -487,6 +487,23 @@ int seq_path(struct seq_file *m, const s
}
EXPORT_SYMBOL(seq_path);

+/**
+ * seq_file_path - seq_file interface to print a pathname of a file
+ * @m: the seq_file handle
+ * @file: the struct file to print
+ * @esc: set of characters to escape in the output
+ *
+ * return the absolute path to the file.
+ */
+int seq_file_path(struct seq_file *m, struct file *file, const char *esc)
+{
+ struct path path;
+
+ f_covering_path(file, &path);
+ return seq_path(m, &path, esc);
+}
+EXPORT_SYMBOL(seq_file_path);
+
/*
* Same as seq_path, but relative to supplied root.
*/
--- a/fs/proc/nommu.c
+++ b/fs/proc/nommu.c
@@ -64,7 +64,7 @@ static int nommu_region_show(struct seq_

if (file) {
seq_pad(m, ' ');
- seq_path(m, &file->f_path, "");
+ seq_file_path(m, file, "");
}

seq_putc(m, '\n');
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -310,7 +310,7 @@ show_map_vma(struct seq_file *m, struct
*/
if (file) {
seq_pad(m, ' ');
- seq_path(m, &file->f_path, "\n");
+ seq_file_path(m, file, "\n");
goto done;
}

@@ -1509,7 +1509,7 @@ static int show_numa_map(struct seq_file

if (file) {
seq_puts(m, " file=");
- seq_path(m, &file->f_path, "\n\t= ");
+ seq_file_path(m, file, "\n\t= ");
} else if (vma->vm_start <= mm->brk && vma->vm_end >= mm->start_brk) {
seq_puts(m, " heap");
} else {
--- a/fs/proc/task_nommu.c
+++ b/fs/proc/task_nommu.c
@@ -180,7 +180,7 @@ static int nommu_vma_show(struct seq_fil

if (file) {
seq_pad(m, ' ');
- seq_path(m, &file->f_path, "");
+ seq_file_path(m, file, "");
} else if (mm) {
pid_t tid = pid_of_stack(priv, vma, is_pid);

--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2032,7 +2032,7 @@ static int swap_show(struct seq_file *sw
}

file = si->swap_file;
- len = seq_path(swap, &file->f_path, " \t\n\\");
+ len = seq_file_path(swap, file, " \t\n\\");
seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
len < 40 ? 40 - len : 1, " ",
S_ISBLK(file_inode(file)->i_mode) ?
--- a/arch/arc/kernel/troubleshoot.c
+++ b/arch/arc/kernel/troubleshoot.c
@@ -67,15 +67,12 @@ void print_task_path_n_nm(struct task_st
mmput(mm);

if (exe_file) {
- path = exe_file->f_path;
- path_get(&exe_file->f_path);
+ path_nm = file_path(exe_file, buf, 255);
fput(exe_file);
- path_nm = d_path(&path, buf, 255);
- path_put(&path);
}

done:
- pr_info("Path: %s\n", path_nm);
+ pr_info("Path: %s\n", !IS_ERR(path_nm) ? path_nm : "?");
}
EXPORT_SYMBOL(print_task_path_n_nm);

@@ -100,8 +97,7 @@ static void show_faulting_vma(unsigned l
if (vma && (vma->vm_start <= address)) {
struct file *file = vma->vm_file;
if (file) {
- struct path *path = &file->f_path;
- nm = d_path(path, buf, PAGE_SIZE - 1);
+ nm = file_path(file, buf, PAGE_SIZE - 1);
inode = file_inode(vma->vm_file);
dev = inode->i_sb->s_dev;
ino = inode->i_ino;
--- a/arch/blackfin/kernel/trace.c
+++ b/arch/blackfin/kernel/trace.c
@@ -136,7 +136,7 @@ void decode_address(char *buf, unsigned
struct file *file = vma->vm_file;

if (file) {
- char *d_name = d_path(&file->f_path, _tmpbuf,
+ char *d_name = file_path(file, _tmpbuf,
sizeof(_tmpbuf));
if (!IS_ERR(d_name))
name = d_name;
--- a/arch/tile/kernel/stack.c
+++ b/arch/tile/kernel/stack.c
@@ -333,7 +333,7 @@ static void describe_addr(struct KBacktr
}

if (vma->vm_file) {
- p = d_path(&vma->vm_file->f_path, buf, bufsize);
+ p = file_path(vma->vm_file, buf, bufsize);
if (IS_ERR(p))
p = "?";
name = kbasename(p);
--- a/arch/tile/mm/elf.c
+++ b/arch/tile/mm/elf.c
@@ -59,7 +59,7 @@ static int notify_exec(struct mm_struct
if (buf == NULL)
return 0;

- path = d_path(&mm->exe_file->f_path, buf, PAGE_SIZE);
+ path = file_path(mm->exe_file, buf, PAGE_SIZE);
if (IS_ERR(path)) {
free_page((unsigned long)buf);
return 0;
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -785,7 +785,7 @@ static void bitmap_file_kick(struct bitm
if (bitmap->storage.file) {
path = kmalloc(PAGE_SIZE, GFP_KERNEL);
if (path)
- ptr = d_path(&bitmap->storage.file->f_path,
+ ptr = file_path(bitmap->storage.file,
path, PAGE_SIZE);

printk(KERN_ALERT
@@ -1786,7 +1786,7 @@ void bitmap_status(struct seq_file *seq,
chunk_kb ? "KB" : "B");
if (bitmap->storage.file) {
seq_printf(seq, ", file: ");
- seq_path(seq, &bitmap->storage.file->f_path, " \t\n");
+ seq_file_path(seq, bitmap->storage.file, " \t\n");
}

seq_printf(seq, "\n");
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5660,7 +5660,7 @@ static int get_bitmap_file(struct mddev
/* bitmap disabled, zero the first byte and copy out */
if (!mddev->bitmap_info.file)
file->pathname[0] = '\0';
- else if ((ptr = d_path(&mddev->bitmap_info.file->f_path,
+ else if ((ptr = file_path(mddev->bitmap_info.file,
file->pathname, sizeof(file->pathname))),
IS_ERR(ptr))
err = PTR_ERR(ptr);
--- a/drivers/usb/gadget/function/f_mass_storage.c
+++ b/drivers/usb/gadget/function/f_mass_storage.c
@@ -2973,7 +2973,7 @@ int fsg_common_create_lun(struct fsg_com
if (fsg_lun_is_open(lun)) {
p = "(error)";
if (pathbuf) {
- p = d_path(&lun->filp->f_path, pathbuf, PATH_MAX);
+ p = file_path(lun->filp, pathbuf, PATH_MAX);
if (IS_ERR(p))
p = "(error)";
}
--- a/drivers/usb/gadget/function/storage_common.c
+++ b/drivers/usb/gadget/function/storage_common.c
@@ -341,7 +341,7 @@ ssize_t fsg_show_file(struct fsg_lun *cu

down_read(filesem);
if (fsg_lun_is_open(curlun)) { /* Get the complete pathname */
- p = d_path(&curlun->filp->f_path, buf, PAGE_SIZE - 1);
+ p = file_path(curlun->filp, buf, PAGE_SIZE - 1);
if (IS_ERR(p))
rc = PTR_ERR(p);
else {
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1535,7 +1535,7 @@ static int fill_files_note(struct memelf
file = vma->vm_file;
if (!file)
continue;
- filename = d_path(&file->f_path, name_curpos, remaining);
+ filename = file_path(file, name_curpos, remaining);
if (IS_ERR(filename)) {
if (PTR_ERR(filename) == -ENAMETOOLONG) {
vfree(data);
@@ -1545,7 +1545,7 @@ static int fill_files_note(struct memelf
continue;
}

- /* d_path() fills at the end, move name down */
+ /* file_path() fills at the end, move name down */
/* n = strlen(filename) + 1: */
n = (name_curpos + remaining) - filename;
remaining = filename - name_curpos;
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -138,7 +138,7 @@ static int cn_print_exe_file(struct core
goto put_exe_file;
}

- path = d_path(&exe_file->f_path, pathbuf, PATH_MAX);
+ path = file_path(exe_file, pathbuf, PATH_MAX);
if (IS_ERR(path)) {
ret = PTR_ERR(path);
goto free_buf;
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -466,7 +466,7 @@ void __ext4_error_file(struct file *file
es = EXT4_SB(inode->i_sb)->s_es;
es->s_last_error_ino = cpu_to_le32(inode->i_ino);
if (ext4_error_ratelimit(inode->i_sb)) {
- path = d_path(&(file->f_path), pathname, sizeof(pathname));
+ path = file_path(file, pathname, sizeof(pathname));
if (IS_ERR(path))
path = "(unknown)";
va_start(args, fmt);
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5594,7 +5594,7 @@ static void perf_event_mmap_event(struct
* need to add enough zero bytes after the string to handle
* the 64bit alignment we do later.
*/
- name = d_path(&file->f_path, buf, PATH_MAX - sizeof(u64));
+ name = file_path(file, buf, PATH_MAX - sizeof(u64));
if (IS_ERR(name)) {
name = "//toolong";
goto cpy_name;
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3627,7 +3627,7 @@ void print_vma_addr(char *prefix, unsign
if (buf) {
char *p;

- p = d_path(&f->f_path, buf, PAGE_SIZE);
+ p = file_path(f, buf, PAGE_SIZE);
if (IS_ERR(p))
p = "?";
printk("%s%s[%lx+%lx]", prefix, kbasename(p),

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