From: Christian Brauner Date: Mon, 14 Apr 2025 20:13:33 +0000 (+0200) Subject: fs: add kern_path_locked_negative() X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=c86b300b1ea35959a6e2a63a6497226a6ea90b67;p=users%2Fhch%2Fmisc.git fs: add kern_path_locked_negative() The audit code relies on the fact that kern_path_locked() returned a path even for a negative dentry. If it doesn't find a valid dentry it immediately calls: audit_find_parent(d_backing_inode(parent_path.dentry)); which assumes that parent_path.dentry is still valid. But it isn't since kern_path_locked() has been changed to path_put() also for a negative dentry. Fix this by adding a helper that implements the required audit semantics and allows us to fix the immediate bleeding. We can find a unified solution for this afterwards. Link: https://lore.kernel.org/20250414-rennt-wimmeln-f186c3a780f1@brauner Fixes: 1c3cb50b58c3 ("VFS: change kern_path_locked() and user_path_locked_at() to never return negative dentry") Reported-and-tested-by: Vlastimil Babka Signed-off-by: Christian Brauner --- diff --git a/fs/namei.c b/fs/namei.c index 8510ff53f12e..267ac9c22dd2 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1665,27 +1665,20 @@ static struct dentry *lookup_dcache(const struct qstr *name, return dentry; } -/* - * Parent directory has inode locked exclusive. This is one - * and only case when ->lookup() gets called on non in-lookup - * dentries - as the matter of fact, this only gets called - * when directory is guaranteed to have no in-lookup children - * at all. - * Will return -ENOENT if name isn't found and LOOKUP_CREATE wasn't passed. - * Will return -EEXIST if name is found and LOOKUP_EXCL was passed. - */ -struct dentry *lookup_one_qstr_excl(const struct qstr *name, - struct dentry *base, - unsigned int flags) +static struct dentry *lookup_one_qstr_excl_raw(const struct qstr *name, + struct dentry *base, + unsigned int flags) { - struct dentry *dentry = lookup_dcache(name, base, flags); + struct dentry *dentry; struct dentry *old; - struct inode *dir = base->d_inode; + struct inode *dir; + dentry = lookup_dcache(name, base, flags); if (dentry) - goto found; + return dentry; /* Don't create child dentry for a dead directory. */ + dir = base->d_inode; if (unlikely(IS_DEADDIR(dir))) return ERR_PTR(-ENOENT); @@ -1698,7 +1691,24 @@ struct dentry *lookup_one_qstr_excl(const struct qstr *name, dput(dentry); dentry = old; } -found: + return dentry; +} + +/* + * Parent directory has inode locked exclusive. This is one + * and only case when ->lookup() gets called on non in-lookup + * dentries - as the matter of fact, this only gets called + * when directory is guaranteed to have no in-lookup children + * at all. + * Will return -ENOENT if name isn't found and LOOKUP_CREATE wasn't passed. + * Will return -EEXIST if name is found and LOOKUP_EXCL was passed. + */ +struct dentry *lookup_one_qstr_excl(const struct qstr *name, + struct dentry *base, unsigned int flags) +{ + struct dentry *dentry; + + dentry = lookup_one_qstr_excl_raw(name, base, flags); if (IS_ERR(dentry)) return dentry; if (d_is_negative(dentry) && !(flags & LOOKUP_CREATE)) { @@ -2762,6 +2772,29 @@ static struct dentry *__kern_path_locked(int dfd, struct filename *name, struct return d; } +struct dentry *kern_path_locked_negative(const char *name, struct path *path) +{ + struct filename *filename __free(putname) = getname_kernel(name); + struct dentry *d; + struct qstr last; + int type, error; + + error = filename_parentat(AT_FDCWD, filename, 0, path, &last, &type); + if (error) + return ERR_PTR(error); + if (unlikely(type != LAST_NORM)) { + path_put(path); + return ERR_PTR(-EINVAL); + } + inode_lock_nested(path->dentry->d_inode, I_MUTEX_PARENT); + d = lookup_one_qstr_excl_raw(&last, path->dentry, 0); + if (IS_ERR(d)) { + inode_unlock(path->dentry->d_inode); + path_put(path); + } + return d; +} + struct dentry *kern_path_locked(const char *name, struct path *path) { struct filename *filename = getname_kernel(name); diff --git a/include/linux/namei.h b/include/linux/namei.h index e3042176cdf4..bbaf55fb3101 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -62,6 +62,7 @@ extern struct dentry *kern_path_create(int, const char *, struct path *, unsigne extern struct dentry *user_path_create(int, const char __user *, struct path *, unsigned int); extern void done_path_create(struct path *, struct dentry *); extern struct dentry *kern_path_locked(const char *, struct path *); +extern struct dentry *kern_path_locked_negative(const char *, struct path *); extern struct dentry *user_path_locked_at(int , const char __user *, struct path *); int vfs_path_parent_lookup(struct filename *filename, unsigned int flags, struct path *parent, struct qstr *last, int *type, diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c index 367eaf2c78b7..0ebbbe37a60f 100644 --- a/kernel/audit_watch.c +++ b/kernel/audit_watch.c @@ -347,12 +347,17 @@ static void audit_remove_parent_watches(struct audit_parent *parent) /* Get path information necessary for adding watches. */ static int audit_get_nd(struct audit_watch *watch, struct path *parent) { - struct dentry *d = kern_path_locked(watch->path, parent); + struct dentry *d; + + d = kern_path_locked_negative(watch->path, parent); if (IS_ERR(d)) return PTR_ERR(d); - /* update watch filter fields */ - watch->dev = d->d_sb->s_dev; - watch->ino = d_backing_inode(d)->i_ino; + + if (d_is_positive(d)) { + /* update watch filter fields */ + watch->dev = d->d_sb->s_dev; + watch->ino = d_backing_inode(d)->i_ino; + } inode_unlock(d_backing_inode(parent->dentry)); dput(d); @@ -418,11 +423,10 @@ int audit_add_watch(struct audit_krule *krule, struct list_head **list) /* caller expects mutex locked */ mutex_lock(&audit_filter_mutex); - if (ret && ret != -ENOENT) { + if (ret) { audit_put_watch(watch); return ret; } - ret = 0; /* either find an old parent or attach a new one */ parent = audit_find_parent(d_backing_inode(parent_path.dentry));