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mount_subtree() pointless use-after-free

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d'oh... we'd carefully pinned mnt->mnt_sb down, dropped mnt and attempt
to grab s_umount on mnt->mnt_sb.  The trouble is, *mnt might've been
overwritten by now...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2011-11-22 12:31:21 -05:00
parent b464133679
commit d31da0f0ba
1 changed files with 4 additions and 2 deletions
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6
fs/namespace.c
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@ -2493,6 +2493,7 @@ EXPORT_SYMBOL(create_mnt_ns);
struct dentry *mount_subtree(struct vfsmount *mnt, const char *name) struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
{ {
struct mnt_namespace *ns; struct mnt_namespace *ns;
struct super_block *s;
struct path path; struct path path;
int err; int err;
@ -2509,10 +2510,11 @@ struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
return ERR_PTR(err); return ERR_PTR(err);
/* trade a vfsmount reference for active sb one */ /* trade a vfsmount reference for active sb one */
atomic_inc(&path.mnt->mnt_sb->s_active); s = path.mnt->mnt_sb;
atomic_inc(&s->s_active);
mntput(path.mnt); mntput(path.mnt);
/* lock the sucker */ /* lock the sucker */
down_write(&path.mnt->mnt_sb->s_umount); down_write(&s->s_umount);
/* ... and return the root of (sub)tree on it */ /* ... and return the root of (sub)tree on it */
return path.dentry; return path.dentry;
} }