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Tue, 25 Mar 2025 04:02:02 -0700 (PDT) MIME-Version: 1.0 References: <67dc67f0.050a0220.25ae54.001f.GAE@google.com> <20250324160003.GA8878@redhat.com> <20250324182722.GA29185@redhat.com> <20250325100936.GC29185@redhat.com> In-Reply-To: <20250325100936.GC29185@redhat.com> From: Mateusz Guzik Date: Tue, 25 Mar 2025 12:01:48 +0100 X-Gm-Features: AQ5f1JpTONFO0gbZ_zxBvlJ_8LU60QgkNDlC1LnIvICNvskd11D8aTb39EJsvyQ Message-ID: Subject: Re: [PATCH] exec: fix the racy usage of fs_struct->in_exec To: Oleg Nesterov Cc: syzbot , brauner@kernel.org, kees@kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 7FB7E180012 X-Stat-Signature: 8i13j9qwdtebwp1mhmu36szzxuin39fj X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1742900946-3835 X-HE-Meta: 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 CFPZKGBB 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.028295, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 25, 2025 at 11:10=E2=80=AFAM Oleg Nesterov wr= ote: > > On 03/24, Mateusz Guzik wrote: > > > > On Mon, Mar 24, 2025 at 7:28=E2=80=AFPM Oleg Nesterov = wrote: > > > > > > So to me it would be better to have the trivial fix for stable, > > > exactly because it is trivially backportable. Then cleanup/simplify > > > this logic on top of it. > > > > So I got myself a crap testcase with a CLONE_FS'ed task which can > > execve and sanity-checked that suid is indeed not honored as expected. > > So you mean my patch can't fix the problem? No, I think the patch works. I am saying the current scheme is avoidably hard to reason about. > > > Anyhow, the plan would be to serialize on the bit, synchronized with > > the current spin lock. copy_fs would call a helper to wait for it to > > clear, would still bump ->users under the spin lock. > > > > This would decouple the handling from cred_mutex and avoid weirdness > > like clearing the ->in_exec flag when we never set it. > > I don't really understand the idea, but as I said I won't argue with > another solution. > I'll try to ship later today so that there will be something concrete to comment on. --=20 Mateusz Guzik