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ALSA: asihpi: fix a potential double-fetch bug when copying puhm 

The hm->h.size is intended to hold the actual size of the hm struct
that is copied from userspace and should always be <= sizeof(*hm).

However, after copy_from_user(hm, puhm, hm->h.size), since userspace
process has full control over the memory region pointed by puhm, it is
possible that the value of hm->h.size is different from what is fetched-in
previously (get_user(hm->h.size, (u16 __user *)puhm)). In other words,
hm->h.size is overriden and the relation between hm->h.size and the hm
struct is broken.

This patch proposes to use a seperate variable, msg_size, to hold
the value of the first fetch and override hm->h.size to msg_size
after the second fetch to maintain the relation.

Signed-off-by: Meng Xu <mengxu.gatech@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Meng Xu 2017-09-19 01:21:56 -04:00 committed by Takashi Iwai
parent a931b9ce93
commit e1af344df4
1 changed files with 8 additions and 4 deletions
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12
sound/pci/asihpi/hpioctl.c
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@ -103,6 +103,7 @@ long asihpi_hpi_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
void __user *puhr;
union hpi_message_buffer_v1 *hm;
union hpi_response_buffer_v1 *hr;
u16 msg_size;
u16 res_max_size;
u32 uncopied_bytes;
int err = 0;
@ -127,22 +128,25 @@ long asihpi_hpi_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
}
/* Now read the message size and data from user space. */
if (get_user(hm->h.size, (u16 __user *)puhm)) {
if (get_user(msg_size, (u16 __user *)puhm)) {
err = -EFAULT;
goto out;
}
if (hm->h.size > sizeof(*hm))
hm->h.size = sizeof(*hm);
if (msg_size > sizeof(*hm))
msg_size = sizeof(*hm);
/* printk(KERN_INFO "message size %d\n", hm->h.wSize); */
uncopied_bytes = copy_from_user(hm, puhm, hm->h.size);
uncopied_bytes = copy_from_user(hm, puhm, msg_size);
if (uncopied_bytes) {
HPI_DEBUG_LOG(ERROR, "uncopied bytes %d\n", uncopied_bytes);
err = -EFAULT;
goto out;
}
/* Override h.size in case it is changed between two userspace fetches */
hm->h.size = msg_size;
if (get_user(res_max_size, (u16 __user *)puhr)) {
err = -EFAULT;
goto out;