[Qemu-devel] [Bug 1783362] Re: qemu-user-aarch64: mmap returns success (NULL, 0) instead of failure (MAP_FAILED, -1) with len==0

[umarcor]

I did some research and found that this bug is present since 2003:

- 2003/05/13: 
https://github.com/qemu/qemu/commit/54936004fddc52c321cb3f9a9a51140e782bed5d#diff-2bf4728e0473404c39c97190bd02b2f8
  - 
https://github.com/qemu/qemu/blob/54936004fddc52c321cb3f9a9a51140e782bed5d/linux-user/mmap.c#L182-L183
- 2008/06/02: 
https://github.com/qemu/qemu/commit/c8a706fe6242a553960ccc3071a4e75ceba6f3d2#diff-2bf4728e0473404c39c97190bd02b2f8
  - 
https://github.com/qemu/qemu/blob/c8a706fe6242a553960ccc3071a4e75ceba6f3d2/linux-user/mmap.c#L284-L285
  - 
https://github.com/qemu/qemu/blob/c8a706fe6242a553960ccc3071a4e75ceba6f3d2/linux-user/mmap.c#L400-L410

It is present in versions 2.11.2, 2.12.0 and master:

- https://github.com/qemu/qemu/blob/v2.11.2/linux-user/mmap.c#L401-L402
- https://github.com/qemu/qemu/blob/v2.12.0/linux-user/mmap.c#L401-L402
- https://github.com/qemu/qemu/blob/master/linux-user/mmap.c#L400-L401

I think that a possible fix is:

@@ -397,8 +397,10 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int 
prot,
     }
 
     len = TARGET_PAGE_ALIGN(len);
-    if (len == 0)
-        goto the_end;
+    if (len == 0) {
+        errno = EINVAL;
+        goto fail;
+    }
     real_start = start & qemu_host_page_mask;
     host_offset = offset & qemu_host_page_mask;

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https://bugs.launchpad.net/bugs/1783362

Title:
  qemu-user-aarch64: mmap returns success (NULL, 0) instead of failure
  (MAP_FAILED, -1) with len==0

Status in QEMU:
  New
Status in qemu package in Ubuntu:
  New

Bug description:
  As shown in https://github.com/beehive-
  lab/mambo/issues/19#issuecomment-407420602, with len==0 mmap returns
  success (NULL, 0) instead of failure (MAP_FAILED, -1) in a x86_64 host
  executing a ELF 64-bit LSB executable, ARM aarch64 binary.

  Steps to reproduce the bug:

  - (cross-)compile the attached source file:

  $ aarch64-linux-gnu-gcc -static -std=gnu99 -lpthread test/mmap_qemu.c
  -o mmap_qemu

  - Execute in a x86_64 host with qemu-user and qemu-user-binfmt:

  $ ./mmap_qemu
  alloc: 0
  MAP_FAILED: -1
  errno: 0
  mmap_qemu: test/mmap_qemu.c:15: main: Assertion `alloc == MAP_FAILED' failed.
  qemu: uncaught target signal 6 (Aborted) - core dumped
  Aborted (core dumped)

  - Execute in a ARM host without any additional dependecy:

  $ ./mmap_qemu
  alloc: -1
  MAP_FAILED: -1
  errno: 22

  The bug is present in Fedora:

  $ qemu-aarch64 --version
  qemu-aarch64 version 2.11.2(qemu-2.11.2-1.fc28)
  Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
  $ uname -r
  4.17.7-200.fc28.x86_64

  And also in Ubuntu:

  $ qemu-aarch64 --version
  qemu-aarch64 version 2.12.0 (Debian 1:2.12+dfsg-3ubuntu3)
  Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
  $ uname -r
  4.15.0-23-generic

  Possibly related to:

  - https://lists.freebsd.org/pipermail/freebsd-hackers/2009-July/029109.html
  - https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203852

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