From: Linus Torvalds Date: Sat, 1 Aug 2009 17:34:56 +0000 (-0700) Subject: do_sigaltstack: avoid copying 'stack_t' as a structure to user space Git-commit: 0083fc2c50e6c5127c2802ad323adf8143ab7856 Patch-mainline: 2.6.31 References: bnc#527848 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 Acked-by: Jeff Mahoney --- kernel/signal.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) --- a/kernel/signal.c +++ b/kernel/signal.c @@ -2353,11 +2353,9 @@ do_sigaltstack (const stack_t __user *us 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; @@ -2400,13 +2398,16 @@ do_sigaltstack (const stack_t __user *us 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; }