linux-user: Don't assert if guest tries shmdt(0)
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>
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 @@
#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 @@
((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 @@
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;
}
