MIPS: Drop spurious __unused in struct compat_flock

BugLink: https://bugs.launchpad.net/bugs/1752317
commit 6ae1756faddefd7494353380ee546dd38c2f97eb upstream.

MIPS' struct compat_flock doesn't match the 32-bit struct flock, as it
has an extra short __unused before pad[4], which combined with alignment
increases the size to 40 bytes compared with struct flock's 36 bytes.

Since commit 8c6657cb50cb ("Switch flock copyin/copyout primitives to
copy_{from,to}_user()"), put_compat_flock() writes the full compat_flock
struct to userland, which results in corruption of the userland word
after the struct flock when running 32-bit userlands on 64-bit kernels.

This was observed to cause a bus error exception when starting Firefox
on Debian 8 (Jessie).

Reported-by: Peter Mamonov <pmamonov@gmail.com>
Signed-off-by: James Hogan <jhogan@kernel.org>
Tested-by: Peter Mamonov <pmamonov@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-mips@linux-mips.org
Cc: <stable@vger.kernel.org> # 4.13+
Patchwork: https://patchwork.linux-mips.org/patch/18646/
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/arch/mips/include/asm/compat.h b/arch/mips/include/asm/compat.h
index 49691331ada4c1b8d8632fc8293a246e657cdb63..08ec0762ca50403466278e7728e0da35914e061b 100644 (file)
--- a/arch/mips/include/asm/compat.h
+++ b/arch/mips/include/asm/compat.h
@@ -86,7 +86,6 @@ struct compat_flock {
        compat_off_t    l_len;
        s32             l_sysid;
        compat_pid_t    l_pid;
-       short           __unused;
        s32             pad[4];
 };