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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Xenial)
       Status: New => Triaged

** Changed in: linux (Ubuntu)
       Status: Confirmed => Triaged

** Changed in: linux (Ubuntu Xenial)
   Importance: Undecided => Medium

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https://bugs.launchpad.net/bugs/1745364

Title:
  x86/net/bpf: return statement missing value

Status in linux package in Ubuntu:
  Triaged
Status in linux source package in Xenial:
  Triaged

Bug description:
  SRU Justification
  =================

  Coverity reports:

  *** CID 1464330:  Uninitialized variables  (MISSING_RETURN)
  /arch/x86/net/bpf_jit_comp.c: 1088 in bpf_int_jit_compile()
  1082            int i;
  1083     1084           if (!bpf_jit_enable)
  1085                    return prog;
  1086     1087           if (!prog || !prog->len)
  >>>     CID 1464330:  Uninitialized variables  (MISSING_RETURN)
  >>>     Arriving at the end of a function without returning a value.
  1088                    return;
  1089     1090           addrs = kmalloc(prog->len * sizeof(*addrs), GFP_KERNEL);
  1091            if (!addrs)
  1092                    return prog;
  1093

  This is a result of 3098d8eae421 ("bpf: prepare
  bpf_int_jit_compile/bpf_prog_select_runtime apis"), which is a cherry-
  pick of d1c55ab5e41f upstream. In that patch, the return type of
  bpf_int_jit_compile was changed from void to struct bpf_prog*. That
  patch changed some of the return statements.

  It did not, however, change the return statement of the (!prog ||
  !prog->len) check, as in upstream the (!prog || !prog->len) check was
  dropped in 93a73d442d37 ("bpf, x86/arm64: remove useless checks on
  prog"):

  """
  There is never such a situation, where bpf_int_jit_compile() is
  called with either prog as NULL or len as 0, so the tests are
  unnecessary and confusing as people would just copy them.
  """

  However, we haven't picked up 93a73d442d37, so when we cherry-picked
  d1c55ab5e41f, that branch remained unmodified, hence the static
  analysis warning.

  Impact
  ======

  If the branch is not dead and someone can hit it, an undefined value
  can be returned, which could cause issues.

  Fix
  ===

  For consistency and in case the branch is not actually dead on Xenial,
  we should do a fixup to 'return prog;'

  Regression Potential
  ====================

  Limited to the BPF jit which is off by default.
  Limited to a branch that should be dead code anyway.
  Limited to an error handling path.

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