getdents[64] misses last entries if some entries are removed between successive calls

[izbyshev]

I'm running Windows 10 1809 10.0.17763.1 (with Ubuntu 18.04) and I've hit what seems to be a variant of #2077. When reading /proc/self/fd, if there are several getdents[64] syscalls and we close some of the descriptors corresponding to the entries we've got after each syscall, we'll stop early.

$ cat test.c
#define _GNU_SOURCE
#include <fcntl.h>
#include <sys/syscall.h>
#include <unistd.h>

int main(void) {
    char buf[100];
    for (int i = 0; i < 10; i++)
        open("/dev/null", O_RDONLY);
    int dfd = open("/proc/self/fd", O_RDONLY);
    int fd = 4;
    while (syscall(SYS_getdents64, dfd, buf, sizeof(buf)) > 0)
        close(fd++);
    close(dfd);
    return 0;
}
$ gcc test.c
$ strace -e openat,close,getdents64 ./a.out
[...]
openat(AT_FDCWD, "/proc/self/fd", O_RDONLY) = 13
getdents64(13, /* 4 entries */, 100)    = 96
close(4)                                = 0
getdents64(13, /* 4 entries */, 100)    = 96
close(5)                                = 0
getdents64(13, /* 4 entries */, 100)    = 96
close(6)                                = 0
getdents64(13, /* 1 entries */, 100)    = 24
close(7)                                = 0
getdents64(13, /* 0 entries */, 100)    = 0
close(13)                               = 0
[...]

The expected strace output is:

openat(AT_FDCWD, "/proc/self/fd", O_RDONLY) = 13
getdents64(13, /* 4 entries */, 100)    = 96
close(4)                                = 0
getdents64(13, /* 4 entries */, 100)    = 96
close(5)                                = 0
getdents64(13, /* 4 entries */, 100)    = 96
close(6)                                = 0
getdents64(13, /* 3 entries */, 100)    = 72
close(7)                                = 0
getdents64(13, /* 0 entries */, 100)    = 0
close(13)                               = 0

The example was reduced from subprocess Python module. Its test suite fails because subprocess uses similar logic to close open descriptors in the child process.

getdents syscall is also affected.

[microsoft-github-policy-service]

This issue has been automatically closed since it has not had any activity for the past year. If you're still experiencing this issue please re-file this as a new issue or feature request.

Thank you!