From: Al Viro Date: Tue, 6 Apr 2021 16:33:07 +0000 (-0400) Subject: Make sure nd->path.mnt and nd->path.dentry are always valid pointers X-Git-Tag: v5.10.162~58 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0cf0ce8fb5b10d669072345ea855de112d0e0a43;p=thirdparty%2Fkernel%2Fstable.git Make sure nd->path.mnt and nd->path.dentry are always valid pointers [ Upstream commit 7d01ef7585c07afaf487759a48486228cd065726 ] Initialize them in set_nameidata() and make sure that terminate_walk() clears them once the pointers become potentially invalid (i.e. we leave RCU mode or drop them in non-RCU one). Currently we have "path_init() always initializes them and nobody accesses them outside of path_init()/terminate_walk() segments", which is asking for trouble. With that change we would have nd->path.{mnt,dentry} 1) always valid - NULL or pointing to currently allocated objects. 2) non-NULL while we are successfully walking 3) NULL when we are not walking at all 4) contributing to refcounts whenever non-NULL outside of RCU mode. Fixes: 6c6ec2b0a3e0 ("fs: add support for LOOKUP_CACHED") Reported-by: syzbot+c88a7030da47945a3cc3@syzkaller.appspotmail.com Tested-by: Christian Brauner Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman --- diff --git a/fs/namei.c b/fs/namei.c index ec6121fb21d87..fc7d562115aea 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -529,6 +529,8 @@ static void set_nameidata(struct nameidata *p, int dfd, struct filename *name) p->stack = p->internal; p->dfd = dfd; p->name = name; + p->path.mnt = NULL; + p->path.dentry = NULL; p->total_link_count = old ? old->total_link_count : 0; p->saved = old; current->nameidata = p; @@ -602,6 +604,8 @@ static void terminate_walk(struct nameidata *nd) rcu_read_unlock(); } nd->depth = 0; + nd->path.mnt = NULL; + nd->path.dentry = NULL; } /* path_put is needed afterwards regardless of success or failure */ @@ -2243,8 +2247,6 @@ static const char *path_init(struct nameidata *nd, unsigned flags) } nd->root.mnt = NULL; - nd->path.mnt = NULL; - nd->path.dentry = NULL; /* Absolute pathname -- fetch the root (LOOKUP_IN_ROOT uses nd->dfd). */ if (*s == '/' && !(flags & LOOKUP_IN_ROOT)) {