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| author | Al Viro <viro@zeniv.linux.org.uk> | 2009-05-08 16:05:57 -0400 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2009-05-09 10:51:34 -0400 |
| commit | 2a32cebd6cbcc43996c3e2d114fa32ba1e71192a (patch) | |
| tree | 0ad94849a7bc3e97cd19978005d1898c8bb44b36 /fs/namespace.c | |
| parent | f9dbd05bc97d1d4f17c2057612f6a8e4dbd039e0 (diff) | |
| download | lwn-2a32cebd6cbcc43996c3e2d114fa32ba1e71192a.tar.gz lwn-2a32cebd6cbcc43996c3e2d114fa32ba1e71192a.zip | |
Fix races around the access to ->s_options
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>
Diffstat (limited to 'fs/namespace.c')
| -rw-r--r-- | fs/namespace.c | 21 |
1 files changed, 18 insertions, 3 deletions
diff --git a/fs/namespace.c b/fs/namespace.c index 0d2003fb4377..134d494158d9 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -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) |