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-rw-r--r--ipc/shm.c19
1 files changed, 11 insertions, 8 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index 0075990338f4..29978ee76c2e 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1371,14 +1371,17 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
if (addr) {
if (addr & (shmlba - 1)) {
- /*
- * Round down to the nearest multiple of shmlba.
- * For sane do_mmap_pgoff() parameters, avoid
- * round downs that trigger nil-page and MAP_FIXED.
- */
- if ((shmflg & SHM_RND) && addr >= shmlba)
- addr &= ~(shmlba - 1);
- else
+ if (shmflg & SHM_RND) {
+ addr &= ~(shmlba - 1); /* round down */
+
+ /*
+ * Ensure that the round-down is non-nil
+ * when remapping. This can happen for
+ * cases when addr < shmlba.
+ */
+ if (!addr && (shmflg & SHM_REMAP))
+ goto out;
+ } else
#ifndef __ARCH_FORCE_SHMLBA
if (addr & ~PAGE_MASK)
#endif