[Bug 1653481] [NEW] Memory leak in libcrypt.so

[Andrew Parker]

Public bug reported:

ubuntu version: 16.04 LTS (also seen in 14.04 and suspect all versions)
glibc version: 2.23

Repeatedly opening libcrypt.so, calling crypt and closing libcrypt.so
leaks memory. I believe the issue is with static arrays which are
allocated on demand but never deallocated. See both md5-crypt.c and
sha256-crypt.c: both these files have a static buffer:

libc_freeres_ptr (static char *buffer);

which is allocated by the __md5_crypt and __sha256_crypt functions
respectively.

This is not a pathological issue. I have encountered it in a real world
use case. The following describes the situation in which it occurred.

- A continuously running process uses PAM to perform authentication.
- PAM module used relies on crypt function call.
- Each call to auth causes libcrypt.so to be loaded and unloaded.
- Result: Small leak in main process each time auth is performed.

Workaround was to force a dependency in the main processes source code
on libcrypt.so thus keeping the library permanently in memory.

I suspect this may be a bug destined for glibc itself rather than the
Ubuntu distribution but, as per glibc guidelines, I'm reporting it here
first. I haven't investigated the source code in enough detail yet to
conclude where the responsibility for the bug lies.

** Affects: glibc (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1653481

Title:
  Memory leak in libcrypt.so

Status in glibc package in Ubuntu:
  New

Bug description:
  ubuntu version: 16.04 LTS (also seen in 14.04 and suspect all versions)
  glibc version: 2.23

  Repeatedly opening libcrypt.so, calling crypt and closing libcrypt.so
  leaks memory. I believe the issue is with static arrays which are
  allocated on demand but never deallocated. See both md5-crypt.c and
  sha256-crypt.c: both these files have a static buffer:

  libc_freeres_ptr (static char *buffer);

  which is allocated by the __md5_crypt and __sha256_crypt functions
  respectively.

  This is not a pathological issue. I have encountered it in a real
  world use case. The following describes the situation in which it
  occurred.

  - A continuously running process uses PAM to perform authentication.
  - PAM module used relies on crypt function call.
  - Each call to auth causes libcrypt.so to be loaded and unloaded.
  - Result: Small leak in main process each time auth is performed.

  Workaround was to force a dependency in the main processes source code
  on libcrypt.so thus keeping the library permanently in memory.

  I suspect this may be a bug destined for glibc itself rather than the
  Ubuntu distribution but, as per glibc guidelines, I'm reporting it
  here first. I haven't investigated the source code in enough detail
  yet to conclude where the responsibility for the bug lies.

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