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

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You have been subscribed to a public bug by Phillip Susi (psusi):

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.

** Affects: util-linux (Ubuntu)
     Importance: Undecided
         Status: New

-- 
Compiler warning about possiable overflow in devname.c
https://bugs.launchpad.net/bugs/1739889
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