[Bug dynamic-link/29317] New: dlsym with RTLD_DEFAULT causes library to be marked as NODELETE (preventing unloading)

["64.delta at proton dot me" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29317

            Bug ID: 29317
           Summary: dlsym with RTLD_DEFAULT causes library to be marked as
                    NODELETE (preventing unloading)
           Product: glibc
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: 64.delta at proton dot me
  Target Milestone: ---

Here is a reproducer, using glibc version 2.35:

$ cat main.c
#include <dlfcn.h>
#include <assert.h>

int main() {
    void *foo = dlopen("libfoo.so", RTLD_GLOBAL | RTLD_NOW);
    assert(foo);

    void *sym = dlsym(RTLD_DEFAULT, "foo");
    // void *sym = dlsym(foo, "foo");
    assert(sym);

    dlclose(foo);

    assert(!dlopen("libfoo.so", RTLD_NOLOAD | RTLD_NOW));
}
$ cat libfoo.c
void foo() {}
$ gcc libfoo.c -shared -o libfoo.so
$ gcc main.c -D_GNU_SOURCE -Wl,-rpath=. && ./a.out
a.out: main.c:14: main: Assertion `!dlopen("libfoo.so", RTLD_NOLOAD |
RTLD_NOW)' failed.

---

Running with LD_DEBUG=all reveals that 'marking ./libfoo.so [0] as NODELETE due
to reference to main program' is printed during the call to dlsym.

If instead the commented line is used in favour of the line above, then the
assertion passes and no such log is printed.

As far as I'm aware there's nothing about RTLD_DEFAULT which would require the
library be marked as NODELETE, so I assume this is a bug.

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