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Wed, 13 Nov 2024 12:55:31 -0500 (EST) From: Erin Shepherd Date: Wed, 13 Nov 2024 17:55:24 +0000 Subject: [PATCH v2 2/3] exportfs: allow fs to disable CAP_DAC_READ_SEARCH check Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20241113-pidfs_fh-v2-2-9a4d28155a37@e43.eu> References: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> In-Reply-To: <20241113-pidfs_fh-v2-0-9a4d28155a37@e43.eu> To: Christian Brauner , Alexander Viro , Jan Kara , Chuck Lever Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jeff Layton , Amir Goldstein , linux-nfs@vger.kernel.org, Erin Shepherd X-Mailer: b4 0.14.2 For pidfs, there is no reason to restrict file handle decoding by CAP_DAC_READ_SEARCH. Introduce an export_ops flag that can indicate this Signed-off-by: Erin Shepherd --- fs/fhandle.c | 36 +++++++++++++++++++++--------------- include/linux/exportfs.h | 3 +++ 2 files changed, 24 insertions(+), 15 deletions(-) diff --git a/fs/fhandle.c b/fs/fhandle.c index 82df28d45cd70a7df525f50bbb398d646110cd99..056116e58f43983bc7bb86da170= fb554c7a2fac7 100644 --- a/fs/fhandle.c +++ b/fs/fhandle.c @@ -235,26 +235,32 @@ static int do_handle_to_path(struct file_handle *hand= le, struct path *path, return 0; } =20 -/* - * Allow relaxed permissions of file handles if the caller has the - * ability to mount the filesystem or create a bind-mount of the - * provided @mountdirfd. - * - * In both cases the caller may be able to get an unobstructed way to - * the encoded file handle. If the caller is only able to create a - * bind-mount we need to verify that there are no locked mounts on top - * of it that could prevent us from getting to the encoded file. - * - * In principle, locked mounts can prevent the caller from mounting the - * filesystem but that only applies to procfs and sysfs neither of which - * support decoding file handles. - */ static inline bool may_decode_fh(struct handle_to_path_ctx *ctx, unsigned int o_flags) { struct path *root =3D &ctx->root; + struct export_operations *nop =3D root->mnt->mnt_sb->s_export_op; + + if (nop && nop->flags & EXPORT_OP_UNRESTRICTED_OPEN) + return true; + + if (capable(CAP_DAC_READ_SEARCH)) + return true; =20 /* + * Allow relaxed permissions of file handles if the caller has the + * ability to mount the filesystem or create a bind-mount of the + * provided @mountdirfd. + * + * In both cases the caller may be able to get an unobstructed way to + * the encoded file handle. If the caller is only able to create a + * bind-mount we need to verify that there are no locked mounts on top + * of it that could prevent us from getting to the encoded file. + * + * In principle, locked mounts can prevent the caller from mounting the + * filesystem but that only applies to procfs and sysfs neither of which + * support decoding file handles. + * * Restrict to O_DIRECTORY to provide a deterministic API that avoids a * confusing api in the face of disconnected non-dir dentries. * @@ -293,7 +299,7 @@ static int handle_to_path(int mountdirfd, struct file_h= andle __user *ufh, if (retval) goto out_err; =20 - if (!capable(CAP_DAC_READ_SEARCH) && !may_decode_fh(&ctx, o_flags)) { + if (!may_decode_fh(&ctx, o_flags)) { retval =3D -EPERM; goto out_path; } diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h index 893a1d21dc1c4abc7e52325d7a4cf0adb407f039..459508b53e77ed0597cee217ffe= 3d82cc7cc11a4 100644 --- a/include/linux/exportfs.h +++ b/include/linux/exportfs.h @@ -247,6 +247,9 @@ struct export_operations { */ #define EXPORT_OP_FLUSH_ON_CLOSE (0x20) /* fs flushes file data on close */ #define EXPORT_OP_ASYNC_LOCK (0x40) /* fs can do async lock request */ +#define EXPORT_OP_UNRESTRICTED_OPEN (0x80) /* FS allows open_by_handle_at + without CAP_DAC_READ_SEARCH + */ unsigned long flags; }; =20 --=20 2.46.1