From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792594705; b=1w4NQWoO7iiRJsSWrm2SGhULJujH7+yoHpJdASUO3OfMCbbFlx59RuJ2piPwvBAzvd0T ELklUEdNZCMmgX8K2lME+jLaNHrfHEIEcHdcB6VhobfFpp20HgUj/ZKCnZw1TCylfdKlP VZ1orRYCgleR3/o+nwkDM1xUjQYX+qBFgJ5g3T4g7Py5t7BI8u2aNui0m4x8NSHahANj7 BPyS3H3WzETYcxhEbFv4RNpK1RfalFIi+65khivlzUntDZipvgAfnuia1GqII5t7cBh82 Mm1GnaBSikVa7ivzkNXk8wtuBK/NFKvy2uxGrz3s6FLBOcvQuXQ0HIKuMB5LJXDX95g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792594705; h=Received:DKIM-Signature:Message-ID:Subject:From:To:Cc:Date: In-Reply-To:References:Autocrypt:Content-Type: Content-Transfer-Encoding:User-Agent:MIME-Version; bh=6fabmKq1+kcDZhL8Hn5LKRXfQ76KTEVC4iI6TGVv4vg=; b=Ie6GtFEBjMWFTMW6+J0ZksXUBIAdVrS0X0/uigF5sFxwSB75DvjSvMY/CwySNehBmEjM 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In-Reply-To: <20261021023715.315727-1-muumthf@gmail.com> References: <20261021023715.315727-1-muumthf@gmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn VluJH0/RcxEeFbnSaswVChNSGa7mXJrTR22lRL6ZPjdMgS2Km90haWPRc8Wolcz07Y2se0xpGVLEQ cDEsvv5IMmeMe1/qLZ6NaVkNuL3WOXvxaVT9USW1+/SGipO2IpKJjeDZfehlB/kpfF24+RrK+seQf CBYyUE8QJpvTZyfUHNYldXlrjO6n5MdOempLqWpfOmcGkwnyNRBR46g/jf8KnPRwXs509yAqDB6sE LZH+yWr9LQZEwARAQABtCVKZWZmIExheXRvbiA8amxheXRvbkBwb29jaGllcmVkcy5uZXQ+iQI7BB 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aEZCiDOq0anx6FmOzs5E6Jqdpo/mtI8beK+BE7Va6ni7YrQlnT0i3vaTVMTiCThbqsB20VrbMjlhp f8lfK1XVNbRq/R7GZ9zHESlsa35ha60yd/j3pu5hT2xyy8krV8vGhHvnJ1XRMJBAB/UYb6FyC7S+m QZIQXVeAA+smfTT0tDrisj1U5x6ZB9b3nBg65kc= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-2.fc44) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Wed, 2026-10-21 at 11:37 +0900, Hyunsol Mun wrote: > nfsd4_encode_listxattrs() reserves 12 bytes for the reply cookie and > array count before it starts encoding attribute names. If the first user > attribute name does not fit in the client's maxcount, the encoder returns > NFS4ERR_TOOSMALL without initializing the reservation. >=20 > The generic COMPOUND encoder does not truncate replies for this error, so > the reserved bytes are transmitted after the operation status and can > disclose stale reply-buffer contents. >=20 > Save the XDR length on entry and restore it whenever the LISTXATTRS > encoder returns an error. This also discards partial output from other > errors after encoding has started. >=20 > Validation used nfsd-testing b4e06bef3884. On the unpatched x86_64 > kernel, all 1,000 NFS4ERR_TOOSMALL replies contained the extra 12-byte > body. The leaked windows reconstructed another client's exact session ID > and enabled cached OPEN replay, stateid use, creation of a new session > for the victim client, and callback-state modification. >=20 > With this patch, two runs totaling 2,000 NFS4ERR_TOOSMALL replies > contained no extra body or leak window, so session reconstruction > failed. The victim's cached OPEN completed normally in both runs. >=20 > A patched-kernel smoke run also completed a successful LISTXATTRS > through an NFSv4.2 mount. NFSv4.2 and NFSv3 read/write/unmount tests > passed. All test kernels built with GCC 13.3 and CONFIG_WERROR, and no > kernel warning, Oops, or panic occurred. The reproducer and complete > logs are available privately on request. >=20 > The vulnerability research and validation were conducted by members of > the Tobabz team as part of the Best of the Best 15th program. >=20 > Fixes: 23e50fe3a5e6 ("nfsd: implement the xattr functions and en/decode l= ogic") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Hyunsol Mun > --- > fs/nfsd/nfs4xdr.c | 3 +++ > 1 file changed, 3 insertions(+) >=20 > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c > index c4fd840da4d9..c7c2be555b59 100644 > --- a/fs/nfsd/nfs4xdr.c > +++ b/fs/nfsd/nfs4xdr.c > @@ -6438,6 +6438,7 @@ nfsd4_encode_listxattrs(struct nfsd4_compoundres *r= esp, __be32 nfserr, > { > struct nfsd4_listxattrs *listxattrs =3D &u->listxattrs; > struct xdr_stream *xdr =3D resp->xdr; > + unsigned int starting_len =3D xdr->buf->len; > u32 cookie_offset, count_offset, eof; > u32 left, xdrleft, slen, count; > u32 xdrlen, offset; > @@ -6545,6 +6546,8 @@ nfsd4_encode_listxattrs(struct nfsd4_compoundres *r= esp, __be32 nfserr, > out: > if (listxattrs->lsxa_len) > kvfree(listxattrs->lsxa_buf); > + if (status) > + xdr_truncate_encode(xdr, starting_len); > return status; > } > =20 >=20 > base-commit: b4e06bef38843c8b909d0b4317dfaaf87dba6d72 Reviewed-by: Jeff Layton