[Bug 1739889] Re: Compiler warning about possiable overflow in devname.c

[Phillip Susi]

** Tags added: patch

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Title:
  Compiler warning about possiable overflow in devname.c

Status in util-linux package in Ubuntu:
  New

Bug description:
  I just compiled mount and got the following warning:

  libblkid/src/devname.c:166:29: warning: ‘%s’ directive writing up to 255 bytes into a region of size 245 [-Wformat-overflow=]
     sprintf(path, "/sys/block/%s/slaves", de->d_name);
                               ^~
  In file included from /usr/include/stdio.h:862:0,
                   from libblkid/src/devname.c:16:
  /usr/include/x86_64-linux-gnu/bits/stdio2.h:33:10: note: ‘__builtin___sprintf_chk’ output between 19 and 274 bytes into a destination of size 256
     return __builtin___sprintf_chk (__s, __USE_FORTIFY_LEVEL - 1,
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         __bos (__s), __fmt, __va_arg_pack ());
         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

  Code preceding this does a length check to prevent overflow. However,
  the warning was still alarming. The attached patch switches sprintf to
  snprintf and ups the buffer size to 300. This will silence the
  compiler and support longer device names. There didn't appear to be
  any technical reason for the 256 byte limit. If there is we just get a
  different less alarming truncation warning. This also means we don't
  need the hard coded length check.

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