Commit 0083fc2c authored Aug 01, 2009 by Linus Torvalds

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 <drepper@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ed680c4a

kernel/signal.c

+8 −7

Original line number	Diff line number	Diff line
		@@ -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);
		}

		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;
		}

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