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>
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@ -8260,16 +8260,22 @@ static int do_openat(CPUArchState *cpu_env, int dirfd, const char *pathname, int
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char filename[PATH_MAX];
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int fd, r;
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/* create temporary file to map stat to */
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tmpdir = getenv("TMPDIR");
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if (!tmpdir)
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tmpdir = "/tmp";
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snprintf(filename, sizeof(filename), "%s/qemu-open.XXXXXX", tmpdir);
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fd = mkstemp(filename);
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fd = memfd_create("qemu-open", 0);
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if (fd < 0) {
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return fd;
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if (errno != ENOSYS) {
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return fd;
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}
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/* create temporary file to map stat to */
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tmpdir = getenv("TMPDIR");
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if (!tmpdir)
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tmpdir = "/tmp";
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snprintf(filename, sizeof(filename), "%s/qemu-open.XXXXXX", tmpdir);
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fd = mkstemp(filename);
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if (fd < 0) {
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return fd;
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}
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unlink(filename);
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}
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unlink(filename);
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if ((r = fake_open->fill(cpu_env, fd))) {
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int e = errno;
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