From 0083fc2c50e6c5127c2802ad323adf8143ab7856 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 1 Aug 2009 10:34:56 -0700 Subject: do_sigaltstack: avoid copying 'stack_t' as a structure to user space Ulrich Drepper correctly points out that there is generally padding in the structure on 64-bit hosts, and that copying the structure from kernel to user space can leak information from the kernel stack in those padding bytes. Avoid the whole issue by just copying the three members one by one instead, which also means that the function also can avoid the need for a stack frame. This also happens to match how we copy the new structure from user space, so it all even makes sense. [ The obvious solution of adding a memset() generates horrid code, gcc does really stupid things. ] Reported-by: Ulrich Drepper Signed-off-by: Linus Torvalds --- kernel/signal.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) (limited to 'kernel/signal.c') diff --git a/kernel/signal.c b/kernel/signal.c index ccf1ceedaebe..f268372c0cc0 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2454,11 +2454,9 @@ do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long s stack_t oss; int error; - if (uoss) { - oss.ss_sp = (void __user *) current->sas_ss_sp; - oss.ss_size = current->sas_ss_size; - oss.ss_flags = sas_ss_flags(sp); - } + oss.ss_sp = (void __user *) current->sas_ss_sp; + oss.ss_size = current->sas_ss_size; + oss.ss_flags = sas_ss_flags(sp); if (uss) { void __user *ss_sp; @@ -2501,13 +2499,16 @@ do_sigaltstack (const stack_t __user *uss, stack_t __user *uoss, unsigned long s current->sas_ss_size = ss_size; } + error = 0; if (uoss) { error = -EFAULT; - if (copy_to_user(uoss, &oss, sizeof(oss))) + if (!access_ok(VERIFY_WRITE, uoss, sizeof(*uoss))) goto out; + error = __put_user(oss.ss_sp, &uoss->ss_sp) | + __put_user(oss.ss_size, &uoss->ss_size) | + __put_user(oss.ss_flags, &uoss->ss_flags); } - error = 0; out: return error; } -- cgit v1.2.3