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[Bug 1849894] Re: hw/scsi/scsi-disk.c line 2554 allocation overflow

From: Launchpad Bug Tracker
Subject: [Bug 1849894] Re: hw/scsi/scsi-disk.c line 2554 allocation overflow
Date: Fri, 09 Jul 2021 04:17:32 -0000

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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  hw/scsi/scsi-disk.c line 2554 allocation overflow

Status in QEMU:

Bug description:
  When compiling qemu from git master (at commit
  03bf012e523ecdf047ac56b2057950247256064d ) on Linux amd64, with gcc-9
  9.2.1 , and using `-march=native -flto`, during linking of most target
  binaries, compiler does detect an issue with allocation in
  scsi_disk_new_request_dump and aborts compilation.

  make[1]: Entering directory '/home/user/qemu/slirp'
  make[1]: Nothing to be done for 'all'.
  make[1]: Leaving directory '/home/user/qemu/slirp'
  nm: stats64.o: no symbols
    LINK    aarch64-softmmu/qemu-system-aarch64
  In function ‘scsi_disk_new_request_dump’,
      inlined from ‘scsi_new_request’ at hw/scsi/scsi-disk.c:2580:9,
      inlined from ‘scsi_new_request’ at hw/scsi/scsi-disk.c:2564:21:
  hw/scsi/scsi-disk.c:2554:19: error: argument 1 value ‘18446744073709551612’ 
exceeds maximum object size 9223372036854775807 
  hw/scsi/scsi-disk.c: In function ‘scsi_new_request’:
  /usr/include/glib-2.0/glib/gmem.h:78:10: note: in a call to allocation 
function ‘g_malloc’ declared here
     78 | gpointer g_malloc         (gsize  n_bytes) G_GNUC_MALLOC 
        |          ^
  lto1: all warnings being treated as errors
  lto-wrapper: fatal error: c++ returned 1 exit status
  compilation terminated.
  /usr/bin/ld: error: lto-wrapper failed
  collect2: error: ld returned 1 exit status

  same happens for most other targets: alpha-softmmu/qemu-system-alpha
  arm-softmmu/qemu-system-arm hppa-softmmu/qemu-system-hppa i386-softmmu
  /qemu-system-i386 lm32-softmmu/qemu-system-lm32 mips-softmmu/qemu-
  system-mips mips64-softmmu/qemu-system-mips64 mips64el-softmmu/qemu-
  system-mips64el mipsel-softmmu/qemu-system-mipsel ppc-softmmu/qemu-
  system-ppc ppc64-softmmu/qemu-system-ppc64 riscv32-softmmu/qemu-
  system-riscv32 riscv64-softmmu/qemu-system-riscv64 s390x-softmmu/qemu-
  system-s390x sh4-softmmu/qemu-system-sh4 sh4eb-softmmu/qemu-system-
  sh4eb sparc-softmmu/qemu-system-sparc sparc64-softmmu/qemu-system-
  sparc64 x86_64-softmmu/qemu-system-x86_64 xtensa-softmmu/qemu-system-
  xtensa xtensaeb-softmmu/qemu-system-xtensaeb

  Notice -softmmu being a common factor here.

  The size of the allocation for the temporary buffer for dumping using
  snprintf is determined based on the size of the buffer via call to
  scsi_cdb_length. I believe the heavy inlining and constant propagation
  makes scsi_cdb_length return -1, so len = -1. Then allocation size is
  5*len + 1, or -4. Which overflows to 2^64 - 4 or so.

  The case of len==-1 from scsi_cdb_length happens if the (buf[0] >> 5)
  is not 0, 1, 2, 4 or 5.

  However, I can't find out how gcc figures out that buf[0] is not one
  of these variables. To me looking at this function, compiler should
  not know anything about buf[0].

  I tried following the chain of calls back, including devirtualize
  alloc_req, and I found scsi_device_alloc_req calling these alloc_req
  callbacks, but it is itself called from scsi_req_new, which is called
  in  get_scsi_requests , just after buf is filled from QEMUFile using
  qemu_get_buffer, which ultimately goes even further into read paths,
  which there might be many AFAIK.

  glib2 version 2.62.1-1

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