diff options
| author | Corinna Vinschen <corinna@vinschen.de> | 2022-08-29 13:25:24 +0300 |
|---|---|---|
| committer | Corinna Vinschen <corinna@vinschen.de> | 2022-08-29 13:25:24 +0300 |
| commit | 717c36c0a4e387a73146c1181b7b89f091176e85 (patch) | |
| tree | 9356ba66ced8412129d42bcc94c6046b2fdf05ca | |
| parent | f59ff93046341e688bc36ea81bddd60eea405e21 (diff) | |
Cygwin: fork: fix a potential hang in fork
while debugging a problem introduced in commit
63b503916d42 ("Cygwin: tls_pathbuf: Use Windows heap")
a hang in fork was encountered using the original implementation
of tls_pathbuf:
Using tmp_pathbuf inside the code block guarded by __malloc_trylock
may call malloc from tmp_pathbuf::w_get and thus trying to lock an
exclusive SRW lock recursively, which results in a deadlock.
Allocate a small SECURITY_ATTRIBUTES block on the stack rather than
allocating a 64K tmp_pathbuf. This avoids the potential malloc call.
Drop the __malloc_trylock call entirely. There must not be a malloc
call inside the frok::parent block guarded by __malloc_lock, and
just trying to lock is too dangerous inside fork while other threads
might actually chage the content of the heap. Additionally, add a
comment frowning on malloc usage inside tis code block.
Fixes: 44a79a6eca3d ("Cygwin: convert malloc lock to SRWLOCK")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
| -rw-r--r-- | winsup/cygwin/fork.cc | 8 | ||||
| -rw-r--r-- | winsup/cygwin/local_includes/cygmalloc.h | 1 |
2 files changed, 5 insertions, 4 deletions
diff --git a/winsup/cygwin/fork.cc b/winsup/cygwin/fork.cc index e4931a286..e553c015a 100644 --- a/winsup/cygwin/fork.cc +++ b/winsup/cygwin/fork.cc @@ -296,7 +296,10 @@ frok::parent (volatile char * volatile stack_here) si.lpReserved2 = (LPBYTE) &ch; si.cbReserved2 = sizeof (ch); - bool locked = __malloc_trylock (); + /* NEVER, EVER, call a function which in turn calls malloc&friends while this + malloc lock is active! */ + __malloc_lock (); + bool locked = true; /* Remove impersonation */ cygheap->user.deimpersonate (); @@ -308,8 +311,7 @@ frok::parent (volatile char * volatile stack_here) ch.silentfail (!*with_forkables); /* fail silently without forkables */ - tmp_pathbuf tp; - PSECURITY_ATTRIBUTES sa = (PSECURITY_ATTRIBUTES) tp.w_get (); + PSECURITY_ATTRIBUTES sa = (PSECURITY_ATTRIBUTES) alloca (1024); if (!sec_user_nih (sa, cygheap->user.saved_sid (), well_known_authenticated_users_sid, PROCESS_QUERY_LIMITED_INFORMATION)) diff --git a/winsup/cygwin/local_includes/cygmalloc.h b/winsup/cygwin/local_includes/cygmalloc.h index 73a2f060b..5e1fe8154 100644 --- a/winsup/cygwin/local_includes/cygmalloc.h +++ b/winsup/cygwin/local_includes/cygmalloc.h @@ -32,7 +32,6 @@ extern "C" void __set_ENOMEM (); #elif defined (__INSIDE_CYGWIN__) # define __malloc_lock() AcquireSRWLockExclusive (&mallock) -# define __malloc_trylock() TryAcquireSRWLockExclusive (&mallock) # define __malloc_unlock() ReleaseSRWLockExclusive (&mallock) extern SRWLOCK NO_COPY mallock; void malloc_init (); |