Message ID | 20200201162645.GJ23230@ZenIV.linux.org.uk (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | fix do_last() regression | expand |
On Sat, Feb 1, 2020 at 8:26 AM Al Viro <viro@zeniv.linux.org.uk> wrote: > > Brown paperbag time: fetching ->i_uid/->i_mode really should've been > done from nd->inode. I'm assuming you want me to apply this directly as a patch, or was it meant as a heads-up with a future pull request? Linus
On Sat, Feb 01, 2020 at 10:29:17AM -0800, Linus Torvalds wrote: > On Sat, Feb 1, 2020 at 8:26 AM Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > Brown paperbag time: fetching ->i_uid/->i_mode really should've been > > done from nd->inode. > > I'm assuming you want me to apply this directly as a patch, or was it > meant as a heads-up with a future pull request? The former, actually, but I can throw it into #fixes and send a pull request if you prefer it that...
On Sat, Feb 1, 2020 at 10:32 AM Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > > I'm assuming you want me to apply this directly as a patch, or was it > > meant as a heads-up with a future pull request? > > The former, actually, but I can throw it into #fixes and send a pull > request if you prefer it that... I've applied it. I just wanted to check, since you end up doing both at times.. Linus
diff --git a/fs/namei.c b/fs/namei.c index 4167109297e0..db6565c99825 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -3333,8 +3333,8 @@ static int do_last(struct nameidata *nd, struct file *file, const struct open_flags *op) { struct dentry *dir = nd->path.dentry; - kuid_t dir_uid = dir->d_inode->i_uid; - umode_t dir_mode = dir->d_inode->i_mode; + kuid_t dir_uid = nd->inode->i_uid; + umode_t dir_mode = nd->inode->i_mode; int open_flag = op->open_flag; bool will_truncate = (open_flag & O_TRUNC) != 0; bool got_write = false;
Brown paperbag time: fetching ->i_uid/->i_mode really should've been done from nd->inode. I even suggested that, but the reason for that has slipped through the cracks and I went for dir->d_inode instead - made for more "obvious" patch. Analysis: at the entry into do_last() and all the way to step_into(): dir (aka nd->path.dentry) is known not to have been freed; so's nd->inode and it's equal to dir->d_inode unless we are already doomed to -ECHILD. inode of the file to get opened is not known. after step_into(): inode of the file to get opened is known; dir might be pointing to freed memory/be negative/etc. at the call of may_create_in_sticky(): guaranteed to be out of RCU mode; inode of the file to get opened is known and pinned; dir might be garbage. The last was the reason for the original patch. Except that at the do_last() entry we can be in RCU mode and it is possible that nd->path.dentry->d_inode has already changed under us. In that case we are going to fail with -ECHILD, but we need to be careful; nd->inode is pointing to valid struct inode and it's the same as nd->path.dentry->d_inode in "won't fail with -ECHILD" case, so we should use that. Reported-by: "Rantala, Tommi T. (Nokia - FI/Espoo)" <tommi.t.rantala@nokia.com> Reported-by: syzbot+190005201ced78a74ad6@syzkaller.appspotmail.com Wearing-brown-paperbag: Al Viro <viro@zeniv.linux.org.uk> Cc: stable@kernel.org Fixes: d0cb50185ae9 (do_last(): fetch directory ->i_mode and ->i_uid before it's too late) Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> ---