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Fix races around the access to ->s_options

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Put generic_show_options read access to s_options under rcu_read_lock,
split save_mount_options() into "we are setting it the first time"
(uses in foo_fill_super()) and "we are relacing and freeing the old one",
synchronize_rcu() before kfree() in the latter.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2009-05-08 16:05:57 -04:00
parent f9dbd05bc9
commit 2a32cebd6c
7 changed files with 25 additions and 13 deletions
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3
drivers/isdn/capi/capifs.c
View file

@ -75,8 +75,7 @@ static int capifs_remount(struct super_block *s, int *flags, char *data)
}
}
kfree(s->s_options);
s->s_options = new_opt;
replace_mount_options(s, new_opt);
config.setuid = setuid;
config.setgid = setgid;

3
fs/affs/super.c
View file

@ -507,8 +507,7 @@ affs_remount(struct super_block *sb, int *flags, char *data)
kfree(new_opts);
return -EINVAL;
}
kfree(sb->s_options);
sb->s_options = new_opts;
replace_mount_options(sb, new_opts);
sbi->s_flags = mount_flags;
sbi->s_mode = mode;

4
fs/afs/super.c
View file

@ -408,17 +408,17 @@ static int afs_get_sb(struct file_system_type *fs_type,
deactivate_locked_super(sb);
goto error;
}
sb->s_options = new_opts;
save_mount_options(sb, new_opts);
sb->s_flags |= MS_ACTIVE;
} else {
_debug("reuse");
kfree(new_opts);
ASSERTCMP(sb->s_flags, &, MS_ACTIVE);
}
simple_set_mnt(mnt, sb);
afs_put_volume(params.volume);
afs_put_cell(params.cell);
kfree(new_opts);
_leave(" = 0 [%p]", sb);
return 0;

3
fs/hpfs/super.c
View file

@ -423,8 +423,7 @@ static int hpfs_remount_fs(struct super_block *s, int *flags, char *data)
if (!(*flags & MS_RDONLY)) mark_dirty(s);
kfree(s->s_options);
s->s_options = new_opts;
replace_mount_options(s, new_opts);
return 0;

21
fs/namespace.c
View file

@ -695,12 +695,16 @@ static inline void mangle(struct seq_file *m, const char *s)
*/
int generic_show_options(struct seq_file *m, struct vfsmount *mnt)
{
const char *options = mnt->mnt_sb->s_options;
const char *options;
rcu_read_lock();
options = rcu_dereference(mnt->mnt_sb->s_options);
if (options != NULL && options[0]) {
seq_putc(m, ',');
mangle(m, options);
}
rcu_read_unlock();
return 0;
}
@ -721,11 +725,22 @@ EXPORT_SYMBOL(generic_show_options);
*/
void save_mount_options(struct super_block *sb, char *options)
{
kfree(sb->s_options);
sb->s_options = kstrdup(options, GFP_KERNEL);
BUG_ON(sb->s_options);
rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
}
EXPORT_SYMBOL(save_mount_options);
void replace_mount_options(struct super_block *sb, char *options)
{
char *old = sb->s_options;
rcu_assign_pointer(sb->s_options, options);
if (old) {
synchronize_rcu();
kfree(old);
}
}
EXPORT_SYMBOL(replace_mount_options);
#ifdef CONFIG_PROC_FS
/* iterator */
static void *m_start(struct seq_file *m, loff_t *pos)

3
fs/reiserfs/super.c
View file

@ -1316,8 +1316,7 @@ static int reiserfs_remount(struct super_block *s, int *mount_flags, char *arg)
}
out_ok:
kfree(s->s_options);
s->s_options = new_opts;
replace_mount_options(s, new_opts);
return 0;
out_err:

1
include/linux/fs.h
View file

@ -2368,6 +2368,7 @@ extern void file_update_time(struct file *file);
extern int generic_show_options(struct seq_file *m, struct vfsmount *mnt);
extern void save_mount_options(struct super_block *sb, char *options);
extern void replace_mount_options(struct super_block *sb, char *options);
static inline ino_t parent_ino(struct dentry *dentry)
{