compat breakage in preadv() and pwritev()

Fix for a dumb preadv()/pwritev() compat bug - unlike the native
variants, the compat_...  ones forget to check FMODE_P{READ,WRITE}, so
e.g.  on pipe the native preadv() will fail with -ESPIPE and compat one
will act as readv() and succeed.

Not critical, but it's a clear bug with trivial fix, so IMO it's OK for
-final.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/fs/compat.c b/fs/compat.c
index f6fd0a00e6cc..691c3fd8ce1d 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1228,7 +1228,9 @@ compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
         file = fget_light(fd, &fput_needed);
         if (!file)
                 return -EBADF;
-        ret = compat_readv(file, vec, vlen, &pos);
+        ret = -ESPIPE;
+        if (file->f_mode & FMODE_PREAD)
+                ret = compat_readv(file, vec, vlen, &pos);
         fput_light(file, fput_needed);
         return ret;
 }
@@ -1285,7 +1287,9 @@ compat_sys_pwritev(unsigned long fd, const struct compat_iovec __user *vec,
         file = fget_light(fd, &fput_needed);
         if (!file)
                 return -EBADF;
-        ret = compat_writev(file, vec, vlen, &pos);
+        ret = -ESPIPE;
+        if (file->f_mode & FMODE_PWRITE)
+                ret = compat_writev(file, vec, vlen, &pos);
         fput_light(file, fput_needed);
         return ret;
 }