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s390/sclp_ctl: fix potential information leak with /dev/sclp 

The sclp_ctl_ioctl_sccb function uses two copy_from_user calls to
retrieve the sclp request from user space. The first copy_from_user
fetches the length of the request which is stored in the first two
bytes of the request. The second copy_from_user gets the complete
sclp request, but this copies the length field a second time.
A malicious user may have changed the length in the meantime.

Reported-by: Pengfei Wang <wpengfeinudt@gmail.com>
Reviewed-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Martin Schwidefsky 2016-04-25 17:54:28 +02:00
parent 723cacbd9d
commit 532c34b5fb
1 changed files with 7 additions and 5 deletions
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12
drivers/s390/char/sclp_ctl.c
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@ -56,6 +56,7 @@ static int sclp_ctl_ioctl_sccb(void __user *user_area)
{
struct sclp_ctl_sccb ctl_sccb;
struct sccb_header *sccb;
unsigned long copied;
int rc;
if (copy_from_user(&ctl_sccb, user_area, sizeof(ctl_sccb)))
@ -65,14 +66,15 @@ static int sclp_ctl_ioctl_sccb(void __user *user_area)
sccb = (void *) get_zeroed_page(GFP_KERNEL | GFP_DMA);
if (!sccb)
return -ENOMEM;
if (copy_from_user(sccb, u64_to_uptr(ctl_sccb.sccb), sizeof(*sccb))) {
copied = PAGE_SIZE -
copy_from_user(sccb, u64_to_uptr(ctl_sccb.sccb), PAGE_SIZE);
if (offsetof(struct sccb_header, length) +
sizeof(sccb->length) > copied || sccb->length > copied) {
rc = -EFAULT;
goto out_free;
}
if (sccb->length > PAGE_SIZE || sccb->length < 8)
return -EINVAL;
if (copy_from_user(sccb, u64_to_uptr(ctl_sccb.sccb), sccb->length)) {
rc = -EFAULT;
if (sccb->length < 8) {
rc = -EINVAL;
goto out_free;
}
rc = sclp_sync_request(ctl_sccb.cmdw, sccb);