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header.b=IOLUgLMb Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F0371F000CA; Wed, 21 Oct 2026 11:55:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792583748; bh=mwwp0gQt9PZ43YZnAx+gKuC2Zifd3eUojBewsisQdYE=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=IOLUgLMbtyDZGJ+OhWHxvruNcUJC2KLHNeKC9RQ/7WJKQ5rgtawKij+f6jRxH2AJn YQvO4FfrGioGuOoHFlovKtzDjMlMwV2gGD2o7Uu9J6CJOXx5bVZercxu4lTj+E+wz2 2kExSteo/iztBuUewK0BLe2nyoOVQymsQWcvnsQT1SXfWs/yM0bX71MdP0XbIbwBNx RsKhC0U4eVEj+6iQw0m+ATf1JU1lVBc0CXpEMZYel73M6enFCKv4zP8JkspcEwyUGf ke/J+WkdAtqWcDnoXXhJx0vvMwefZmT0t291RMuY9CeE2vjCNXjLwdLQ1KVl8gAFnw zo8ZQ/exvUtSw== Message-ID: <33ec91ed2a10afecee87c08b623f3d6f6949a4f7.camel@kernel.org> Subject: Re: [PATCH 5/6] listns: don't wrap around with a U64_MAX cursor From: Jeff Layton To: Christian Brauner , linux-fsdevel@vger.kernel.org Cc: Alexander Viro , Jan Kara , Miklos Szeredi , shaos , linux-kernel@vger.kernel.org, stable@vger.kernel.org Date: Wed, 21 Oct 2026 07:55:45 -0400 In-Reply-To: <20261021-work-mount-statmount_listns_fixes-v1-5-8917a4c1bd14@kernel.org> References: <20261021-work-mount-statmount_listns_fixes-v1-0-8917a4c1bd14@kernel.org> <20261021-work-mount-statmount_listns_fixes-v1-5-8917a4c1bd14@kernel.org> 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 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Yy9YbXtWctUz8uvDR7shsQxAhX3qO7DilMtuGo1v97I/Kx4gXQ52syh/w6EBny71CZrOgD6kJwPVV AaM1LRC28muq91WCFhs/nzHozpbzcheyGtMUI2Ao4K6mnY+3zIuXPygZMFr9KXE6fF7HzKxKuZMJO 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 13:46 +0200, Christian Brauner wrote: > do_listns() and do_listns_userns() take the last namespace id the caller > saw and look up the first namespace after it by searching the rbtree for > last_ns_id + 1. With U64_MAX that wraps around to zero and the search > returns the namespace with the smallest id. So a cursor at the largest > possible id restarts the listing from the beginning instead of failing > with ENOENT like a cursor of U64_MAX - 1 does. That's the case for the > unified tree, the type-specific trees and the owner tree alike. >=20 > No namespace will ever have that id. They come from a counter and a > caller that only feeds back ids it got from us can't hit this. It's > still wrong. >=20 > Instead of adding one to the cursor and searching for the smallest id > that's greater or equal make the lookup helpers search for the smallest > id that's strictly greater than the cursor. That's what both callers > want anyway and there's nothing left to overflow. >=20 > Reproducer, unprivileged: >=20 > #define _GNU_SOURCE > #include > #include > #include > #include > #include > #ifndef __NR_listns > #define __NR_listns 470 > #endif > #define CLONE_NEWUSER 0x10000000U > #define LISTNS_CURRENT_USER 0xffffffffffffffffULL > struct ns_id_req { > uint32_t size, spare; > uint64_t ns_id; > uint32_t ns_type, spare2; > uint64_t user_ns_id; > }; > static void list(const char *tree, uint32_t type, uint64_t owner, > uint64_t cursor) > { > struct ns_id_req req =3D { > .size =3D sizeof(req), .ns_id =3D cursor, .ns_type =3D type, > .user_ns_id =3D owner, > }; > uint64_t ids[8]; > long ret; > errno =3D 0; > ret =3D syscall(__NR_listns, &req, ids, 8, 0); > printf("%s cursor %llu: ret %ld errno %d", tree, > (unsigned long long)cursor, ret, errno); > for (long i =3D 0; i < ret && i < 3; i++) > printf("%s%llu", i ? "," : " ids ", (unsigned long long)ids[i]); > printf("%s\n", ret > 3 ? ",..." : ""); > } > int main(void) > { > static const uint64_t cursors[] =3D { 0, UINT64_MAX - 1, UINT64_MAX = }; > for (int i =3D 0; i < 3; i++) > list("unified", 0, 0, cursors[i]); > for (int i =3D 0; i < 3; i++) > list("userns", CLONE_NEWUSER, 0, cursors[i]); > for (int i =3D 0; i < 3; i++) > list("owner", 0, LISTNS_CURRENT_USER, cursors[i]); > return 0; > } >=20 > Before, on 7.3.0-rc7-00252-g4e3259b08c54 (vfs.fixes) in a VM: >=20 > unified cursor 0: ret 8 errno 0 ids 1,2,3,... > unified cursor 18446744073709551614: ret -1 errno 2 > unified cursor 18446744073709551615: ret 8 errno 0 ids 1,2,3,... > userns cursor 0: ret 1 errno 0 ids 3 > userns cursor 18446744073709551614: ret -1 errno 2 > userns cursor 18446744073709551615: ret 1 errno 0 ids 3 > owner cursor 0: ret 8 errno 0 ids 1,2,4,... > owner cursor 18446744073709551614: ret -1 errno 2 > owner cursor 18446744073709551615: ret 8 errno 0 ids 1,2,4,... >=20 > After: >=20 > unified cursor 0: ret 8 errno 0 ids 1,2,3,... > unified cursor 18446744073709551614: ret -1 errno 2 > unified cursor 18446744073709551615: ret -1 errno 2 > userns cursor 0: ret 1 errno 0 ids 3 > userns cursor 18446744073709551614: ret -1 errno 2 > userns cursor 18446744073709551615: ret -1 errno 2 > owner cursor 0: ret 8 errno 0 ids 1,2,4,... > owner cursor 18446744073709551614: ret -1 errno 2 > owner cursor 18446744073709551615: ret -1 errno 2 >=20 > Reported-by: shaos > Link: https://lore.kernel.org/r/20261020110732.959552-1-shawnq1@163.com > Fixes: 76b6f5dfb3fd ("nstree: add listns()") > Cc: stable@vger.kernel.org > Signed-off-by: Christian Brauner (Amutable) > --- > kernel/nstree.c | 29 +++++++++++------------------ > 1 file changed, 11 insertions(+), 18 deletions(-) >=20 > diff --git a/kernel/nstree.c b/kernel/nstree.c > index 831f279d174a..58b2b55fa8d2 100644 > --- a/kernel/nstree.c > +++ b/kernel/nstree.c > @@ -459,10 +459,10 @@ static inline int prepare_klistns(struct klistns *k= ls, struct ns_id_req *kreq, > } > =20 > /* > - * Lookup a namespace owned by owner with id >=3D ns_id. > - * Returns the namespace with the smallest id that is >=3D ns_id. > + * Lookup a namespace owned by owner with id > ns_id. > + * Returns the namespace with the smallest id that is > ns_id. > */ > -static struct ns_common *lookup_ns_owner_at(u64 ns_id, struct ns_common = *owner) > +static struct ns_common *lookup_ns_owner_after(u64 ns_id, struct ns_comm= on *owner) > { > struct ns_common *ret =3D NULL; > struct rb_node *node; > @@ -476,10 +476,8 @@ static struct ns_common *lookup_ns_owner_at(u64 ns_i= d, struct ns_common *owner) > struct ns_common *ns; > =20 > ns =3D node_to_ns_owner(node); > - if (ns_id <=3D ns->ns_id) { > + if (ns_id < ns->ns_id) { > ret =3D ns; > - if (ns_id =3D=3D ns->ns_id) > - break; > node =3D node->rb_left; > } else { > node =3D node->rb_right; > @@ -565,7 +563,7 @@ static ssize_t do_listns_userns(struct klistns *kls) > * then use it's list entry to iterate from there. > */ > if (kls->last_ns_id) { > - kls->first_ns =3D lookup_ns_owner_at(kls->last_ns_id + 1, ns); > + kls->first_ns =3D lookup_ns_owner_after(kls->last_ns_id, ns); > if (!kls->first_ns) > return -ENOENT; > first_ns =3D kls->first_ns; > @@ -613,10 +611,10 @@ static ssize_t do_listns_userns(struct klistns *kls= ) > } > =20 > /* > - * Lookup a namespace with id >=3D ns_id in either the unified tree or a= type-specific tree. > - * Returns the namespace with the smallest id that is >=3D ns_id. > + * Lookup a namespace with id > ns_id in either the unified tree or a ty= pe-specific tree. > + * Returns the namespace with the smallest id that is > ns_id. > */ > -static struct ns_common *lookup_ns_id_at(u64 ns_id, int ns_type) > +static struct ns_common *lookup_ns_id_after(u64 ns_id, int ns_type) > { > struct ns_common *ret =3D NULL; > struct ns_tree_root *ns_tree =3D NULL; > @@ -643,13 +641,8 @@ static struct ns_common *lookup_ns_id_at(u64 ns_id, = int ns_type) > else > ns =3D node_to_ns_unified(node); > =20 > - if (ns_id <=3D ns->ns_id) { > - if (ns_type) > - ret =3D node_to_ns(node); > - else > - ret =3D node_to_ns_unified(node); > - if (ns_id =3D=3D ns->ns_id) > - break; > + if (ns_id < ns->ns_id) { > + ret =3D ns; > node =3D node->rb_left; > } else { > node =3D node->rb_right; > @@ -708,7 +701,7 @@ static ssize_t do_listns(struct klistns *kls) > } > =20 > if (kls->last_ns_id) { > - kls->first_ns =3D lookup_ns_id_at(kls->last_ns_id + 1, ns_type); > + kls->first_ns =3D lookup_ns_id_after(kls->last_ns_id, ns_type); > if (!kls->first_ns) > return -ENOENT; > first_ns =3D kls->first_ns; Reviewed-by: Jeff Layton