From 5b63de6b54add51822db3c89325c6fc05534a54c Mon Sep 17 00:00:00 2001 From: =?utf8?q?Rainer=20M=C3=BCller?= Date: Fri, 29 Jul 2022 17:49:51 +0200 Subject: [PATCH] linux-user: Use memfd for open syscall emulation MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit For certain paths in /proc, the open syscall is intercepted and the returned file descriptor points to a temporary file with emulated contents. If TMPDIR is not accessible or writable for the current user (for example in a read-only mounted chroot or container) tools such as ps from procps may fail unexpectedly. Trying to read one of these paths such as /proc/self/stat would return an error such as ENOENT or EROFS. To relax the requirement on a writable TMPDIR, use memfd_create() instead to create an anonymous file and return its file descriptor. Signed-off-by: Rainer Müller Reviewed-by: Richard Henderson Message-Id: <20220729154951.76268-1-raimue@codingfarm.de> Signed-off-by: Laurent Vivier --- linux-user/syscall.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index b27a6552aa..ef53feb5ab 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -8260,16 +8260,22 @@ static int do_openat(CPUArchState *cpu_env, int dirfd, const char *pathname, int char filename[PATH_MAX]; int fd, r; - /* create temporary file to map stat to */ - tmpdir = getenv("TMPDIR"); - if (!tmpdir) - tmpdir = "/tmp"; - snprintf(filename, sizeof(filename), "%s/qemu-open.XXXXXX", tmpdir); - fd = mkstemp(filename); + fd = memfd_create("qemu-open", 0); if (fd < 0) { - return fd; + if (errno != ENOSYS) { + return fd; + } + /* create temporary file to map stat to */ + tmpdir = getenv("TMPDIR"); + if (!tmpdir) + tmpdir = "/tmp"; + snprintf(filename, sizeof(filename), "%s/qemu-open.XXXXXX", tmpdir); + fd = mkstemp(filename); + if (fd < 0) { + return fd; + } + unlink(filename); } - unlink(filename); if ((r = fake_open->fill(cpu_env, fd))) { int e = errno; -- 2.11.0