mm: fix vm_brk_flags() to not bail out while holding lock

Calling vm_brk_flags() with flags set other than VM_EXEC will exit the
function without releasing the mmap_write_lock.

Just do the sanity check before the lock is acquired.  This doesn't fix an
actual issue since no caller sets a flag other than VM_EXEC.

Link: https://lkml.kernel.org/r/20230929171937.work.697-kees@kernel.org
Fixes: 2e7ce7d354f2 ("mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()")
Signed-off-by: Sebastian Ott <sebott@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index b56a7f0..7ed2866 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3143,13 +3143,13 @@ int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
        if (!len)
                return 0;
 
-       if (mmap_write_lock_killable(mm))
-               return -EINTR;
-
        /* Until we need other flags, refuse anything except VM_EXEC. */
        if ((flags & (~VM_EXEC)) != 0)
                return -EINVAL;
 
+       if (mmap_write_lock_killable(mm))
+               return -EINTR;
+
        ret = check_brk_limits(addr, len);
        if (ret)
                goto limits_failed;