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[PULL,v2,4/8] linux-user: Don't assert if guest tries shmdt(0)

Message ID b6e17875f2e4d1ebfd45bcb0eed04c3157e86a84.1456397907.git.riku.voipio@linaro.org
State New
Headers show

Commit Message

Riku Voipio Feb. 25, 2016, 11:01 a.m. UTC 
From: Peter Maydell <peter.maydell@linaro.org>

Our implementation of shmat() and shmdt() for linux-user was
using "zero guest address" as its marker for "entry in the
shm_regions[] array is not in use". This meant that if the
guest did a shmdt(0) we would match on an unused array entry
and call page_set_flags() with both start and end addresses zero,
which causes an assertion failure.

Use an explicit in_use flag to manage the shm_regions[] array,
so that we avoid this problem.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reported-by: Pavel Shamis <pasharesearch@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
---
 linux-user/syscall.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)
diff mbox

Patch

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index dac5518..8b76169 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -2598,8 +2598,9 @@  static abi_long do_socketcall(int num, abi_ulong vptr)
 #define N_SHM_REGIONS	32
 
 static struct shm_region {
-    abi_ulong	start;
-    abi_ulong	size;
+    abi_ulong start;
+    abi_ulong size;
+    bool in_use;
 } shm_regions[N_SHM_REGIONS];
 
 struct target_semid_ds
@@ -3291,7 +3292,8 @@  static inline abi_ulong do_shmat(int shmid, abi_ulong shmaddr, int shmflg)
                    ((shmflg & SHM_RDONLY)? 0 : PAGE_WRITE));
 
     for (i = 0; i < N_SHM_REGIONS; i++) {
-        if (shm_regions[i].start == 0) {
+        if (!shm_regions[i].in_use) {
+            shm_regions[i].in_use = true;
             shm_regions[i].start = raddr;
             shm_regions[i].size = shm_info.shm_segsz;
             break;
@@ -3308,8 +3310,8 @@  static inline abi_long do_shmdt(abi_ulong shmaddr)
     int i;
 
     for (i = 0; i < N_SHM_REGIONS; ++i) {
-        if (shm_regions[i].start == shmaddr) {
-            shm_regions[i].start = 0;
+        if (shm_regions[i].in_use && shm_regions[i].start == shmaddr) {
+            shm_regions[i].in_use = false;
             page_set_flags(shmaddr, shmaddr + shm_regions[i].size, 0);
             break;
         }