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[82.29.237.198]) by smtp.gmail.com with ESMTPSA id f9sm1605939wrm.48.2021.06.28.08.31.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Jun 2021 08:31:29 -0700 (PDT) Date: Mon, 28 Jun 2021 16:31:27 +0100 From: "Dr. David Alan Gilbert" To: Vivek Goyal Subject: Re: [PATCH v7 2/7] virtiofsd: Fix xattr operations overwriting errno Message-ID: References: <20210622150852.1507204-1-vgoyal@redhat.com> <20210622150852.1507204-3-vgoyal@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210622150852.1507204-3-vgoyal@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.375, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: virtio-fs@redhat.com, miklos@szeredi.hu, qemu-devel@nongnu.org, lhenriques@suse.de Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Vivek Goyal (vgoyal@redhat.com) wrote: > getxattr/setxattr/removexattr/listxattr operations handle regualar > and non-regular files differently. For the case of non-regular files > we do fchdir(/proc/self/fd) and the xattr operation and then revert > back to original working directory. After this we are saving errno > and that's buggy because fchdir() will overwrite the errno. > > FCHDIR_NOFAIL(lo->proc_self_fd); > ret = getxattr(procname, name, value, size); > FCHDIR_NOFAIL(lo->root.fd); > > if (ret == -1) > saverr = errno > > In above example, if getxattr() failed, we will still return 0 to caller > as errno must have been written by FCHDIR_NOFAIL(lo->root.fd) call. > Fix all such instances and capture "errno" early and save in "saverr" > variable. > > Signed-off-by: Vivek Goyal I think the existing code is actually safe; I don't think fchdir will/should set errno unless there's an error, and we're explictly asserting there isn't one. However, I do prefer doing this save since we already have the save variables and it makes the chance of screwing it up from any other forgotten syscall less likely, so Reviewed-by: Dr. David Alan Gilbert > --- > tools/virtiofsd/passthrough_ll.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index 49c21fd855..ec91b3c133 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -2791,15 +2791,17 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, > goto out_err; > } > ret = fgetxattr(fd, name, value, size); > + saverr = ret == -1 ? errno : 0; > } else { > /* fchdir should not fail here */ > FCHDIR_NOFAIL(lo->proc_self_fd); > ret = getxattr(procname, name, value, size); > + saverr = ret == -1 ? errno : 0; > FCHDIR_NOFAIL(lo->root.fd); > } > > if (ret == -1) { > - goto out_err; > + goto out; > } > if (size) { > saverr = 0; > @@ -2864,15 +2866,17 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size) > goto out_err; > } > ret = flistxattr(fd, value, size); > + saverr = ret == -1 ? errno : 0; > } else { > /* fchdir should not fail here */ > FCHDIR_NOFAIL(lo->proc_self_fd); > ret = listxattr(procname, value, size); > + saverr = ret == -1 ? errno : 0; > FCHDIR_NOFAIL(lo->root.fd); > } > > if (ret == -1) { > - goto out_err; > + goto out; > } > if (size) { > saverr = 0; > @@ -2998,15 +3002,15 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name, > goto out; > } > ret = fsetxattr(fd, name, value, size, flags); > + saverr = ret == -1 ? errno : 0; > } else { > /* fchdir should not fail here */ > FCHDIR_NOFAIL(lo->proc_self_fd); > ret = setxattr(procname, name, value, size, flags); > + saverr = ret == -1 ? errno : 0; > FCHDIR_NOFAIL(lo->root.fd); > } > > - saverr = ret == -1 ? errno : 0; > - > out: > if (fd >= 0) { > close(fd); > @@ -3064,15 +3068,15 @@ static void lo_removexattr(fuse_req_t req, fuse_ino_t ino, const char *in_name) > goto out; > } > ret = fremovexattr(fd, name); > + saverr = ret == -1 ? errno : 0; > } else { > /* fchdir should not fail here */ > FCHDIR_NOFAIL(lo->proc_self_fd); > ret = removexattr(procname, name); > + saverr = ret == -1 ? errno : 0; > FCHDIR_NOFAIL(lo->root.fd); > } > > - saverr = ret == -1 ? errno : 0; > - > out: > if (fd >= 0) { > close(fd); > -- > 2.25.4 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK