From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 22A771CC8BC; Tue, 19 Nov 2024 12:51:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732020701; cv=none; b=ZjJYzYOArInMATxKwsVqXb98VVv1K/iu/qB7A/i+/T0pX7t6S0xLqV/gbCLfMdOp4aFQ2zhslJLhJt0ECuWvBhAAPuRtj5JULxHdf/odtPJ8Ii5SajLEcvWY593H5lybN1QTNpcnSXYpw9ZuP/cRcnGhGjr46BMU6HlhVYUJN5c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732020701; c=relaxed/simple; bh=CYlciGdisAmlcyRDW/E/lbRtufVuEm6swslvY0z5xng=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=MiIjp2zJBWxIE0wRJbLsmccGrQtzJzz471eUHxlsohQkfZ9Dv6FmMOB1YX8oppqoTmTkGMdrlxHCoiK2fN+n63HXIeluNx8dK8tgFIS9TQT8+oaCmubk3/dieiIo6MrOkivmnc7OUrFaKi1Ge7362MHXh6tS8MRfDjB0IY0aNzE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PTC3urpe; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PTC3urpe" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 05427C4CECF; Tue, 19 Nov 2024 12:51:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732020700; bh=CYlciGdisAmlcyRDW/E/lbRtufVuEm6swslvY0z5xng=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=PTC3urpeNTEGb8tEoqpxg/9ULLhej78qKZTA4xzMPwHcTKZ+yt/h8H7kkxxG68qJj p3t0igMOOSjr9Rm1EgpdKUn7QqQ/Sc9cicVpiJpbksiuzgcWILIKr1vaWklb77XhMo dRPXyy4jbW+45uFnaQuGz77qMRExVNkiY/EiuoKu+UL0+OtEd3vaWJuRDnJSjJKZwd 70SncVbEYGbexsPDgOUO0RHRIFEN0PY/0+bnZixUlc5WIjoFKIGgyt2gmOSDftHvzk 1XO6sj8z2EklPcUbc8tGBDP7q02mqVl8RJ/QwnhQDv2z3IMp9QipYHLZ0oS4gWNg1W C1p0/0IkU+jMg== Message-ID: Subject: Re: [PATCH] fs/ceph/mds_client: give up on paths longer than PATH_MAX From: Jeff Layton To: Ilya Dryomov , Max Kellermann , Patrick Donnelly , Venky Shankar Cc: xiubli@redhat.com, ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org, dario@cure53.de, stable@vger.kernel.org Date: Tue, 19 Nov 2024 07:51:38 -0500 In-Reply-To: References: <20241118222828.240530-1-max.kellermann@ionos.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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11:28=E2=80=AFPM Max Kellermann > wrote: > >=20 > > If the full path to be built by ceph_mdsc_build_path() happens to be > > longer than PATH_MAX, then this function will enter an endless (retry) > > loop, effectively blocking the whole task. Most of the machine > > becomes unusable, making this a very simple and effective DoS > > vulnerability. > >=20 > > I cannot imagine why this retry was ever implemented, but it seems > > rather useless and harmful to me. Let's remove it and fail with > > ENAMETOOLONG instead. >=20 > Hi Max, >=20 > When this was put in place in 2009, I think the idea of a retry was > copied from CIFS. Jeff preserved the retry when he massaged this code > to not warn in case a rename race is detected [1]. CIFS got rid of it > only a couple of years ago [2][3]. >=20 > Adding Patrick and Venky as well, please chime in. >=20 > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co= mmit/?id=3Df5946bcc5e79038f9f7cb66ec25bd3b2d39b2775 > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co= mmit/?id=3Df6a9bc336b600e1266e6eebb0972d75d5b93aea9 > [3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co= mmit/?id=3D991e72eb0e99764219865b9a3a07328695148e14 >=20 > Thanks, >=20 > Ilya >=20 > >=20 > > Cc: stable@vger.kernel.org > > Reported-by: Dario Wei=C3=9Fer > > Signed-off-by: Max Kellermann > > --- > > fs/ceph/mds_client.c | 9 ++++----- > > 1 file changed, 4 insertions(+), 5 deletions(-) > >=20 > > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c > > index c4a5fd94bbbb..4f6ac015edcd 100644 > > --- a/fs/ceph/mds_client.c > > +++ b/fs/ceph/mds_client.c > > @@ -2808,12 +2808,11 @@ char *ceph_mdsc_build_path(struct ceph_mds_clie= nt *mdsc, struct dentry *dentry, > >=20 > > if (pos < 0) { > > /* > > - * A rename didn't occur, but somehow we didn't end up = where > > - * we thought we would. Throw a warning and try again. > > + * The path is longer than PATH_MAX and this function > > + * cannot ever succeed. Creating paths that long is > > + * possible with Ceph, but Linux cannot use them. > > */ > > - pr_warn_client(cl, "did not end path lookup where expec= ted (pos =3D %d)\n", > > - pos); > > - goto retry; > > + return ERR_PTR(-ENAMETOOLONG); > > } > >=20 > > *pbase =3D base; > > -- > > 2.45.2 > >=20 I think the idea was that if we ended up with a path longer than PATH_MAX that something must have changed in the middle of the reverse pathwalk to make it too long a path, and we should just go and try it again. At the very least, this code should cap the retries to a certain number if you don't just return an error here. -ENAMETOOLONG could be problematic there. This function is often called when we have a dentry and need to build a path to it to send to the MDS in a call. The system call that caused us to generate this path probably doesn't involve a pathname itself, so the caller may be confused by an -ENAMETOOLONG return. You may want to go with a more generic error code here -- -EIO or something. It might also be worthwhile to leave in a pr_warn_once or something since there may be users confused by this error return. --=20 Jeff Layton