dynlink.c: bug in reclaim_gaps leading to segfault in __libc_exit_fini

[Hugues Bruant <hugues@aerofs.com>]

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Affects both 1.1.12 and 1.1.13

Tracked down with valgrind in Alpine Linux 3.3.

The dmg tool build from https://github.com/aerofs/libdmg-hfsplus links to a
handful shared libs. The following message is seen immediately at start:

==59== Invalid free() / delete / delete[] / realloc()
==59==    at 0x4C92B0E: free (vg_replace_malloc.c:530)
==59==    by 0x4056F68: reclaim_gaps (dynlink.c:488)
==59==    by 0x405743D: map_library (dynlink.c:708)
==59==    by 0x4057EF3: load_library (dynlink.c:1014)
==59==    by 0x4058CA8: load_preload (dynlink.c:1112)
==59==    by 0x4058CA8: __dls3 (dynlink.c:1581)
==59==    by 0x405856A: __dls2 (dynlink.c:1383)
==59==    by 0x405655E: ??? (in /lib/ld-musl-x86_64.so.1)
==59==    by 0x3: ???
==59==    by 0xFFF000E3A: ???
==59==    by 0xFFF000E3E: ???
==59==    by 0xFFF000E44: ???
==59==    by 0xFFF000E86: ???

Afterwards, the program proceeds with no issue, until it exists, at which
point a segfault is triggered when cleaning up shared libraries:

==38== Invalid read of size 8
==38==    at 0x4057551: decode_vec.constprop.5 (dynlink.c:171)
==38==    by 0x405825C: __libc_exit_fini (dynlink.c:1197)
==38==    by 0x4016233: exit (exit.c:31)
==38==    by 0x401D635: (below main) (__libc_start_main.c:74)
==38==  Address 0x636f8f53ebff9f53 is not stack'd, malloc'd or (recently) free'd
==38==
==38==
==38== Process terminating with default action of signal 11 (SIGSEGV)
==38==  General Protection Fault
==38==    at 0x4057551: decode_vec.constprop.5 (dynlink.c:171)
==38==    by 0x405825C: __libc_exit_fini (dynlink.c:1197)
==38==    by 0x4016233: exit (exit.c:31)
==38==    by 0x401D635: (below main) (__libc_start_main.c:74)
==38==


The first 32 bytes of one of the dso struct are manifestly corrupted.

Patching reclaim_gap as follows fixes the segfault:

diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 87f3b7f..f897dbd 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -484,9 +484,9 @@ static void reclaim_gaps(struct dso *dso)
        for (; phcnt--; ph=(void *)((char *)ph+dso->phentsize)) {
                if (ph->p_type!=PT_LOAD) continue;
                if ((ph->p_flags&(PF_R|PF_W))!=(PF_R|PF_W)) continue;
-               reclaim(dso, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
-               reclaim(dso, ph->p_vaddr+ph->p_memsz,
-                       ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
+               //reclaim(dso, ph->p_vaddr & -PAGE_SIZE, ph->p_vaddr);
+               //reclaim(dso, ph->p_vaddr+ph->p_memsz,
+               //      ph->p_vaddr+ph->p_memsz+PAGE_SIZE-1 & -PAGE_SIZE);
        }
 }


For more details: https://bugs.alpinelinux.org/issues/5123

Regards,
Hugues

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