From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by passt.top (Postfix, from userid 1000) id A5DA05A0623; Mon, 28 Oct 2024 11:00:44 +0100 (CET) From: Stefano Brivio To: passt-dev@passt.top Subject: [PATCH v3 9/9] util: Don't use errno after a successful call in __daemon() Date: Mon, 28 Oct 2024 11:00:44 +0100 Message-ID: <20241028100044.939714-10-sbrivio@redhat.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20241028100044.939714-1-sbrivio@redhat.com> References: <20241028100044.939714-1-sbrivio@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Message-ID-Hash: O4WHE4QLNSNFRBZIXXPUAKTFRIBN3OFQ X-Message-ID-Hash: O4WHE4QLNSNFRBZIXXPUAKTFRIBN3OFQ X-MailFrom: sbrivio@passt.top X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: David Gibson X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: I thought we could just set errno to 0, do a bunch of stuff, and check that errno didn't change to infer we succeeded. But clang-tidy, starting with LLVM 19, reports: /home/sbrivio/passt/util.c:465:6: error: An undefined value may be read from 'errno' [clang-analyzer-unix.Errno,-warnings-as-errors] 465 | if (errno) | ^ /usr/include/errno.h:38:16: note: expanded from macro 'errno' 38 | # define errno (*__errno_location ()) | ^~~~~~~~~~~~~~~~~~~~~~ /home/sbrivio/passt/util.c:446:6: note: Assuming the condition is false 446 | if (pid == -1) { | ^~~~~~~~~ /home/sbrivio/passt/util.c:446:2: note: Taking false branch 446 | if (pid == -1) { | ^ /home/sbrivio/passt/util.c:451:6: note: Assuming 'pid' is 0 451 | if (pid) { | ^~~ /home/sbrivio/passt/util.c:451:2: note: Taking false branch 451 | if (pid) { | ^ /home/sbrivio/passt/util.c:463:2: note: Assuming that 'close' is successful; 'errno' becomes undefined after the call 463 | close(devnull_fd); | ^~~~~~~~~~~~~~~~~ /home/sbrivio/passt/util.c:465:6: note: An undefined value may be read from 'errno' 465 | if (errno) | ^ /usr/include/errno.h:38:16: note: expanded from macro 'errno' 38 | # define errno (*__errno_location ()) | ^~~~~~~~~~~~~~~~~~~~~~ And the LLVM documentation for the unix.Errno checker, 1.1.8.3 unix.Errno (C), mentions, at: https://clang.llvm.org/docs/analyzer/checkers.html#unix-errno that: The C and POSIX standards often do not define if a standard library function may change value of errno if the call does not fail. Therefore, errno should only be used if it is known from the return value of a function that the call has failed. which is, somewhat surprisingly, the case for close(). Instead of using errno, check the actual return values of the calls we issue here. Signed-off-by: Stefano Brivio Reviewed-by: David Gibson --- util.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/util.c b/util.c index d838b34..7f32c95 100644 --- a/util.c +++ b/util.c @@ -443,16 +443,11 @@ int __daemon(int pidfile_fd, int devnull_fd) exit(EXIT_SUCCESS); } - errno = 0; - - setsid(); - - dup2(devnull_fd, STDIN_FILENO); - dup2(devnull_fd, STDOUT_FILENO); - dup2(devnull_fd, STDERR_FILENO); - close(devnull_fd); - - if (errno) + if (setsid() < 0 || + dup2(devnull_fd, STDIN_FILENO) < 0 || + dup2(devnull_fd, STDOUT_FILENO) < 0 || + dup2(devnull_fd, STDERR_FILENO) < 0 || + close(devnull_fd)) exit(EXIT_FAILURE); return 0; -- 2.43.0