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-rw-r--r--ipc/shm.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/ipc/shm.c b/ipc/shm.c
index d7805acb44fd..06ea9ef7f54a 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1091,8 +1091,8 @@ out_unlock1:
* "raddr" thing points to kernel space, and there has to be a wrapper around
* this.
*/
-long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
- unsigned long shmlba)
+long do_shmat(int shmid, char __user *shmaddr, int shmflg,
+ ulong *raddr, unsigned long shmlba)
{
struct shmid_kernel *shp;
unsigned long addr;
@@ -1113,8 +1113,13 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
goto out;
else if ((addr = (ulong)shmaddr)) {
if (addr & (shmlba - 1)) {
- if (shmflg & SHM_RND)
- addr &= ~(shmlba - 1); /* round down */
+ /*
+ * 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
#ifndef __ARCH_FORCE_SHMLBA
if (addr & ~PAGE_MASK)

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