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([2600:1700:6476:1430:ae19:b6b2:5990:ed2a]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7ea20ea8191sm39278017b3.8.2026.06.04.12.54.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Jun 2026 12:54:39 -0700 (PDT) Message-ID: Subject: Re: [PATCH 2/4] ceph: bound MDSCapAuth path and fs_name decode in handle_session() From: Viacheslav Dubeyko To: Michael Bommarito , Ilya Dryomov , Alex Markuze Cc: ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 04 Jun 2026 12:54:37 -0700 In-Reply-To: <54eb585e03930ade4d11d9a103eff5f737d65251.1780596023.git.michael.bommarito@gmail.com> References: <54eb585e03930ade4d11d9a103eff5f737d65251.1780596023.git.michael.bommarito@gmail.com> Autocrypt: addr=slava@dubeyko.com; prefer-encrypt=mutual; keydata=mQINBGgaTLYBEADaJc/WqWTeunGetXyyGJ5Za7b23M/ozuDCWCp+yWUa2GqQKH40dxRIR zshgOmAue7t9RQJU9lxZ4ZHWbi1Hzz85+0omefEdAKFmxTO6+CYV0g/sapU0wPJws3sC2Pbda9/eJ ZcvScAX2n/PlhpTnzJKf3JkHh3nM1ACO3jzSe2/muSQJvqMLG2D71ccekr1RyUh8V+OZdrPtfkDam V6GOT6IvyE+d+55fzmo20nJKecvbyvdikWwZvjjCENsG9qOf3TcCJ9DDYwjyYe1To8b+mQM9nHcxp jUsUuH074BhISFwt99/htZdSgp4csiGeXr8f9BEotRB6+kjMBHaiJ6B7BIlDmlffyR4f3oR/5hxgy dvIxMocqyc03xVyM6tA4ZrshKkwDgZIFEKkx37ec22ZJczNwGywKQW2TGXUTZVbdooiG4tXbRBLxe ga/NTZ52ZdEkSxAUGw/l0y0InTtdDIWvfUT+WXtQcEPRBE6HHhoeFehLzWL/o7w5Hog+0hXhNjqte fzKpI2fWmYzoIb6ueNmE/8sP9fWXo6Av9m8B5hRvF/hVWfEysr/2LSqN+xjt9NEbg8WNRMLy/Y0MS p5fgf9pmGF78waFiBvgZIQNuQnHrM+0BmYOhR0JKoHjt7r5wLyNiKFc8b7xXndyCDYfniO3ljbr0j tXWRGxx4to6FwARAQABtCZWaWFjaGVzbGF2IER1YmV5a28gPHNsYXZhQGR1YmV5a28uY29tPokCVw QTAQoAQQIbAQUJA8JnAAULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBFXDC2tnzsoLQtrbBDlc2cL fhEB1BQJoGl5PAhkBAAoJEDlc2cLfhEB17DsP/jy/Dx19MtxWOniPqpQf2s65enkDZuMIQ94jSg7B F2qTKIbNR9SmsczjyjC+/J7m7WZRmcqnwFYMOyNfh12aF2WhjT7p5xEAbvfGVYwUpUrg/lcacdT0D Yk61GGc5ZB89OAWHLr0FJjI54bd7kn7E/JRQF4dqNsxU8qcPXQ0wLHxTHUPZu/w5Zu/cO+lQ3H0Pj pSEGaTAh+tBYGSvQ4YPYBcV8+qjTxzeNwkw4ARza8EjTwWKP2jWAfA/ay4VobRfqNQ2zLoo84qDtN Uxe0zPE2wobIXELWkbuW/6hoQFPpMlJWz+mbvVms57NAA1HO8F5c1SLFaJ6dN0AQbxrHi45/cQXla 9hSEOJjxcEnJG/ZmcomYHFneM9K1p1K6HcGajiY2BFWkVet9vuHygkLWXVYZ0lr1paLFR52S7T+cf 6dkxOqu1ZiRegvFoyzBUzlLh/elgp3tWUfG2VmJD3lGpB3m5ZhwQ3rFpK8A7cKzgKjwPp61Me0o9z HX53THoG+QG+o0nnIKK7M8+coToTSyznYoq9C3eKeM/J97x9+h9tbizaeUQvWzQOgG8myUJ5u5Dr4 6tv9KXrOJy0iy/dcyreMYV5lwODaFfOeA4Lbnn5vRn9OjuMg1PFhCi3yMI4lA4umXFw0V2/OI5rgW BQELhfvW6mxkihkl6KLZX8m1zcHitCpWaWFjaGVzbGF2IER1YmV5a28gPFNsYXZhLkR1YmV5a29Aa WJtLmNvbT6JAlQEEwEKAD4WIQRVwwtrZ87KC0La2wQ5XNnC34RAdQUCaBpd7AIbAQUJA8JnAAULCQ gHAgYVCgkICwIEFgIDAQIeAQIXgAAKCRA5XNnC34RAdYjFEACiWBEybMt1xjRbEgaZ3UP5i2bSway DwYDvgWW5EbRP7JcqOcZ2vkJwrK3gsqC3FKpjOPh7ecE0I4vrabH1Qobe2N8B2Y396z24mGnkTBbb 16Uz3PC93nFN1BA0wuOjlr1/oOTy5gBY563vybhnXPfSEUcXRd28jI7z8tRyzXh2tL8ZLdv1u4vQ8 E0O7lVJ55p9yGxbwgb5vXU4T2irqRKLxRvU80rZIXoEM7zLf5r7RaRxgwjTKdu6rYMUOfoyEQQZTD 4Xg9YE/X8pZzcbYFs4IlscyK6cXU0pjwr2ssjearOLLDJ7ygvfOiOuCZL+6zHRunLwq2JH/RmwuLV mWWSbgosZD6c5+wu6DxV15y7zZaR3NFPOR5ErpCFUorKzBO1nA4dwOAbNym9OGkhRgLAyxwpea0V0 ZlStfp0kfVaSZYo7PXd8Bbtyjali0niBjPpEVZdgtVUpBlPr97jBYZ+L5GF3hd6WJFbEYgj+5Af7C UjbX9DHweGQ/tdXWRnJHRzorxzjOS3003ddRnPtQDDN3Z/XzdAZwQAs0RqqXrTeeJrLppFUbAP+HZ TyOLVJcAAlVQROoq8PbM3ZKIaOygjj6Yw0emJi1D9OsN2UKjoe4W185vamFWX4Ba41jmCPrYJWAWH fAMjjkInIPg7RLGs8FiwxfcpkILP0YbVWHiNAabQoVmlhY2hlc2xhdiBEdWJleWtvIDx2ZHViZXlr b0BrZXJuZWwub3JnPokCVAQTAQoAPhYhBFXDC2tnzsoLQtrbBDlc2cLfhEB1BQJoVemuAhsBBQkDw mcABQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEDlc2cLfhEB1GRwP/1scX5HO9Sk7dRicLD/fxo ipwEs+UbeA0/TM8OQfdRI4C/tFBYbQCR7lD05dfq8VsYLEyrgeLqP/iRhabLky8LTaEdwoAqPDc/O 9HRffx/faJZqkKc1dZryjqS6b8NExhKOVWmDqN357+Cl/H4hT9wnvjCj1YEqXIxSd/2Pc8+yw/KRC AP7jtRzXHcc/49Lpz/NU5irScusxy2GLKa5o/13jFK3F1fWX1wsOJF8NlTx3rLtBy4GWHITwkBmu8 zI4qcJGp7eudI0l4xmIKKQWanEhVdzBm5UnfyLIa7gQ2T48UbxJlWnMhLxMPrxgtC4Kos1G3zovEy Ep+fJN7D1pwN9aR36jVKvRsX7V4leIDWGzCdfw1FGWkMUfrRwgIl6i3wgqcCP6r9YSWVQYXdmwdMu 1RFLC44iF9340S0hw9+30yGP8TWwd1mm8V/+zsdDAFAoAwisi5QLLkQnEsJSgLzJ9daAsE8KjMthv hUWHdpiUSjyCpigT+KPl9YunZhyrC1jZXERCDPCQVYgaPt+Xbhdjcem/ykv8UVIDAGVXjuk4OW8la nf8SP+uxkTTDKcPHOa5rYRaeNj7T/NClRSd4z6aV3F6pKEJnEGvv/DFMXtSHlbylhyiGKN2Amd0b4 9jg+DW85oNN7q2UYzYuPwkHsFFq5iyF1QggiwYYTpoVXsw Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.1 (by Flathub.org) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2026-06-04 at 14:08 -0400, Michael Bommarito wrote: > handle_session() decodes the MDSCapAuth records carried by a > CEPH_SESSION_OPEN message (msg_version >=3D 6). For each record the > match.path and match.fs_name byte strings are read by first decoding > a > 32-bit length and then copying that many bytes with the bare > ceph_decode_copy(). Unlike the surrounding fields, which all use the > _safe decode variants, these two copies are not preceded by a > ceph_decode_need() bounds check, and the enclosing MDSCapAuth and > MDSCapMatch struct_len fields are skipped rather than enforced as an > upper bound. A length larger than the bytes remaining in the message > front makes ceph_decode_copy() read past the end of the front buffer. >=20 > The message front is a dedicated allocation (ceph_msg_new2() -> > kvmalloc), so the over-read runs off that object. A malicious or > compromised MDS can trigger this with the first post-connect message > on > mount, with no client-side user interaction; under KASAN it is > reported > as a slab-out-of-bounds read in handle_session(). >=20 > Impact: a malicious MDS can force the kernel client to read up to 4 > GiB > past the message front allocation during session setup, crashing the > client (out-of-bounds read). >=20 > Switch both copies to ceph_decode_copy_safe(), which performs the > ceph_decode_need() bounds check before the copy and branches to the > existing bad label, matching the rest of the decoder and the error > path > that frees the partially decoded cap_auths array. >=20 > Fixes: 1d17de9534cb ("ceph: save cap_auths in MDS client when session > is opened") > Cc: stable@vger.kernel.org > Signed-off-by: Michael Bommarito > Assisted-by: Claude:claude-opus-4-8 > --- > =C2=A0fs/ceph/mds_client.c | 8 ++++++-- > =C2=A01 file changed, 6 insertions(+), 2 deletions(-) >=20 > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c > index ed17e0023705e..4f36ac73305dc 100644 > --- a/fs/ceph/mds_client.c > +++ b/fs/ceph/mds_client.c > @@ -4318,7 +4318,9 @@ static void handle_session(struct > ceph_mds_session *session, > =C2=A0 pr_err_client(cl, "No memory > for path\n"); > =C2=A0 goto fail; > =C2=A0 } > - ceph_decode_copy(&p, > cap_auths[i].match.path, _len); > + ceph_decode_copy_safe(&p, end, > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 > cap_auths[i].match.path, > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 _len, bad); > =C2=A0 > =C2=A0 /* Remove the tailing '/' */ > =C2=A0 while (_len && > cap_auths[i].match.path[_len - 1] =3D=3D '/') { > @@ -4335,7 +4337,9 @@ static void handle_session(struct > ceph_mds_session *session, > =C2=A0 pr_err_client(cl, "No memory > for fs_name\n"); > =C2=A0 goto fail; > =C2=A0 } > - ceph_decode_copy(&p, > cap_auths[i].match.fs_name, _len); > + ceph_decode_copy_safe(&p, end, > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 > cap_auths[i].match.fs_name, > + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 _len, bad); > =C2=A0 } > =C2=A0 > =C2=A0 ceph_decode_8_safe(&p, end, > cap_auths[i].match.root_squash, bad); Looks good. Reviewed-by: Viacheslav Dubeyko Thanks, Slava.