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debugfs: add mode, uid and gid options 

Cautious admins may want to restrict access to debugfs. Currently a
manual chown/chmod e.g. in an init script is needed to achieve that.
Distributions that want to make the mount options configurable need
to add extra config files. By allowing to set the root inode's uid,
gid and mode via mount options no such hacks are needed anymore.
Instead configuration becomes straight forward via fstab.

Signed-off-by: Ludwig Nussel <ludwig.nussel@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
hifive-unleashed-5.1
Ludwig Nussel 2012-01-25 11:52:28 +01:00 committed by Greg Kroah-Hartman
parent 9875bb480c
commit d6e486868c
2 changed files with 152 additions and 2 deletions
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5
Documentation/filesystems/debugfs.txt
View File

@ -14,7 +14,10 @@ Debugfs is typically mounted with a command like:
mount -t debugfs none /sys/kernel/debug
(Or an equivalent /etc/fstab line).
(Or an equivalent /etc/fstab line).
The debugfs root directory is accessible by anyone by default. To
restrict access to the tree the "uid", "gid" and "mode" mount
options can be used.
Note that the debugfs API is exported GPL-only to modules.

149
fs/debugfs/inode.c
View File

@ -23,9 +23,13 @@
#include <linux/debugfs.h>
#include <linux/fsnotify.h>
#include <linux/string.h>
#include <linux/seq_file.h>
#include <linux/parser.h>
#include <linux/magic.h>
#include <linux/slab.h>
#define DEBUGFS_DEFAULT_MODE 0755
static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;
static bool debugfs_registered;
@ -125,11 +129,154 @@ static inline int debugfs_positive(struct dentry *dentry)
return dentry->d_inode && !d_unhashed(dentry);
}
struct debugfs_mount_opts {
uid_t uid;
gid_t gid;
umode_t mode;
};
enum {
Opt_uid,
Opt_gid,
Opt_mode,
Opt_err
};
static const match_table_t tokens = {
{Opt_uid, "uid=%u"},
{Opt_gid, "gid=%u"},
{Opt_mode, "mode=%o"},
{Opt_err, NULL}
};
struct debugfs_fs_info {
struct debugfs_mount_opts mount_opts;
};
static int debugfs_parse_options(char *data, struct debugfs_mount_opts *opts)
{
substring_t args[MAX_OPT_ARGS];
int option;
int token;
char *p;
opts->mode = DEBUGFS_DEFAULT_MODE;
while ((p = strsep(&data, ",")) != NULL) {
if (!*p)
continue;
token = match_token(p, tokens, args);
switch (token) {
case Opt_uid:
if (match_int(&args[0], &option))
return -EINVAL;
opts->uid = option;
break;
case Opt_gid:
if (match_octal(&args[0], &option))
return -EINVAL;
opts->gid = option;
break;
case Opt_mode:
if (match_octal(&args[0], &option))
return -EINVAL;
opts->mode = option & S_IALLUGO;
break;
/*
* We might like to report bad mount options here;
* but traditionally debugfs has ignored all mount options
*/
}
}
return 0;
}
static int debugfs_apply_options(struct super_block *sb)
{
struct debugfs_fs_info *fsi = sb->s_fs_info;
struct inode *inode = sb->s_root->d_inode;
struct debugfs_mount_opts *opts = &fsi->mount_opts;
inode->i_mode &= ~S_IALLUGO;
inode->i_mode |= opts->mode;
inode->i_uid = opts->uid;
inode->i_gid = opts->gid;
return 0;
}
static int debugfs_remount(struct super_block *sb, int *flags, char *data)
{
int err;
struct debugfs_fs_info *fsi = sb->s_fs_info;
err = debugfs_parse_options(data, &fsi->mount_opts);
if (err)
goto fail;
debugfs_apply_options(sb);
fail:
return err;
}
static int debugfs_show_options(struct seq_file *m, struct dentry *root)
{
struct debugfs_fs_info *fsi = root->d_sb->s_fs_info;
struct debugfs_mount_opts *opts = &fsi->mount_opts;
if (opts->uid != 0)
seq_printf(m, ",uid=%u", opts->uid);
if (opts->gid != 0)
seq_printf(m, ",gid=%u", opts->gid);
if (opts->mode != DEBUGFS_DEFAULT_MODE)
seq_printf(m, ",mode=%o", opts->mode);
return 0;
}
static const struct super_operations debugfs_super_operations = {
.statfs = simple_statfs,
.remount_fs = debugfs_remount,
.show_options = debugfs_show_options,
};
static int debug_fill_super(struct super_block *sb, void *data, int silent)
{
static struct tree_descr debug_files[] = {{""}};
struct debugfs_fs_info *fsi;
int err;
return simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
save_mount_options(sb, data);
fsi = kzalloc(sizeof(struct debugfs_fs_info), GFP_KERNEL);
sb->s_fs_info = fsi;
if (!fsi) {
err = -ENOMEM;
goto fail;
}
err = debugfs_parse_options(data, &fsi->mount_opts);
if (err)
goto fail;
err = simple_fill_super(sb, DEBUGFS_MAGIC, debug_files);
if (err)
goto fail;
sb->s_op = &debugfs_super_operations;
debugfs_apply_options(sb);
return 0;
fail:
kfree(fsi);
sb->s_fs_info = NULL;
return err;
}
static struct dentry *debug_mount(struct file_system_type *fs_type,