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+ --- Resend mainly so it lands in patchwork. --- arch/mips/include/asm/compat.h | 1 - 1 file changed, 1 deletion(-)
diff --git a/arch/mips/include/asm/compat.h b/arch/mips/include/asm/compat.h index 946681db8dc3..9a0fa66b81ac 100644 --- 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]; };