1 files changed, 8 insertions, 2 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index d1b2b8d934bb..38509dc1f77b 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2018,7 +2018,11 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
                         return error;
         }
 
-        down_write(&mm->mmap_sem);
+        /*
+         * arg_lock protects concurent updates but we still need mmap_sem for
+         * read to exclude races with sys_brk.
+         */
+        down_read(&mm->mmap_sem);
 
         /*
          * We don't validate if these members are pointing to
@@ -2032,6 +2036,7 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
          *    to any problem in kernel itself
          */
 
+        spin_lock(&mm->arg_lock);
         mm->start_code  = prctl_map.start_code;
         mm->end_code    = prctl_map.end_code;
         mm->start_data  = prctl_map.start_data;
@@ -2043,6 +2048,7 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
         mm->arg_end     = prctl_map.arg_end;
         mm->env_start   = prctl_map.env_start;
         mm->env_end     = prctl_map.env_end;
+        spin_unlock(&mm->arg_lock);
 
         /*
          * Note this update of @saved_auxv is lockless thus
@@ -2055,7 +2061,7 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
         if (prctl_map.auxv_size)
                 memcpy(mm->saved_auxv, user_auxv, sizeof(user_auxv));
 
-        up_write(&mm->mmap_sem);
+        up_read(&mm->mmap_sem);
         return 0;
 }
 #endif /* CONFIG_CHECKPOINT_RESTORE */