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do_sigaltstack: avoid copying 'stack_t' as a structure to user space

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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>
This commit is contained in:
Linus Torvalds 2009-08-01 10:34:56 -07:00
parent ed680c4ad4
commit 0083fc2c50
1 changed files with 8 additions and 7 deletions
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15
kernel/signal.c
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@ -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;
}