[Bug stdio/19464] New: getdelim leaks line when n is zero

["msebor at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=19464

            Bug ID: 19464
           Summary: getdelim leaks line when n is zero
           Product: glibc
           Version: 2.23
            Status: NEW
          Severity: normal
          Priority: P2
         Component: stdio
          Assignee: unassigned at sourceware dot org
          Reporter: msebor at redhat dot com
  Target Milestone: ---

Created attachment 8901
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8901&action=edit
Test case.

When called with a non-null *lineptr argument but *n zero, the getdelim (and
getline) functions set the *lineptr pointer to point at a newly allocated block
without freeing the previous block first.  This results in the originally
allocated block leaking.

When linked against current glibc, the attached test case produces the
following output:

fopen("/usr/include/errno.h", "r")
malloc(560) ==> 0x604100
malloc(1248) ==> 0x604330
getdelim(&0x604330, &0)
malloc(128) ==> 0x604810
malloc(4096) ==> 0x604890
realloc(0x604810, 2368) ==> 0x605890
  ==> 2367 (Success)
free(0x605890)
getdelim leaked initally allocated block 0x604330

Compiling the test program with -DDO_NOT_REPLACE_MALLOC=1 and running it under
valgrind includes the following in the output:

==30160== HEAP SUMMARY:
==30160==     in use at exit: 1,786 bytes in 2 blocks
==30160==   total heap usage: 6 allocs, 4 frees, 9,394 bytes allocated
==30160== 
==30160== 1,234 bytes in 1 blocks are definitely lost in loss record 2 of 2
==30160==    at 0x4A06BCF: malloc (in
/usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==30160==    by 0x4007D9: main (in
/home/msebor/build/glibc-trunk/libio/tst-getdelim)

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