linux-user: Use memfd for open syscall emulation
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 <raimue@codingfarm.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220729154951.76268-1-raimue@codingfarm.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index b27a655..ef53feb 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8260,16 +8260,22 @@
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;
