nommu: check fd read permission in validate_mmap_request()

According to the POSIX (1003.1-2008), the file descriptor shall have been
opened with read permission, regardless of the protection options specified to
mmap().  The ltp test cases mmap06/07 need this.

Signed-off-by: Graff Yang <graff.yang@gmail.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/mm/nommu.c b/mm/nommu.c
index 28754c40be98..4bde489ec431 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -919,6 +919,10 @@ static int validate_mmap_request(struct file *file,
                 if (!file->f_op->read)
                         capabilities &= ~BDI_CAP_MAP_COPY;
 
+                /* The file shall have been opened with read permission. */
+                if (!(file->f_mode & FMODE_READ))
+                        return -EACCES;
+
                 if (flags & MAP_SHARED) {
                         /* do checks for writing, appending and locking */
                         if ((prot & PROT_WRITE) &&