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Groups > linux.kernel > #1735415 > unrolled thread
| Started by | Meng Xu <mengxu.gatech@gmail.com> |
|---|---|
| First post | 2017-09-20 05:20 +0200 |
| Last post | 2017-09-21 05:40 +0200 |
| Articles | 4 — 3 participants |
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[PATCH] mpt3sas: downgrade full copy_from_user to access_ok check Meng Xu <mengxu.gatech@gmail.com> - 2017-09-20 05:20 +0200
Re: [PATCH] mpt3sas: downgrade full copy_from_user to access_ok check Christoph Hellwig <hch@infradead.org> - 2017-09-20 17:10 +0200
Re: [PATCH] mpt3sas: downgrade full copy_from_user to access_ok check Al Viro <viro@ZenIV.linux.org.uk> - 2017-09-21 05:30 +0200
Re: [PATCH] mpt3sas: downgrade full copy_from_user to access_ok check Meng Xu <mengxu.gatech@gmail.com> - 2017-09-21 05:40 +0200
| From | Meng Xu <mengxu.gatech@gmail.com> |
|---|---|
| Date | 2017-09-20 05:20 +0200 |
| Subject | [PATCH] mpt3sas: downgrade full copy_from_user to access_ok check |
| Message-ID | <urDIl-5IT-11@gated-at.bofh.it> |
Since right after the user copy, we are going to
memset(&karg, 0, sizeof(karg)), I guess an access_ok check is enough?
Signed-off-by: Meng Xu <mengxu.gatech@gmail.com>
---
drivers/scsi/mpt3sas/mpt3sas_ctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/scsi/mpt3sas/mpt3sas_ctl.c b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
index bdffb69..b363d2d 100644
--- a/drivers/scsi/mpt3sas/mpt3sas_ctl.c
+++ b/drivers/scsi/mpt3sas/mpt3sas_ctl.c
@@ -1065,7 +1065,7 @@ _ctl_getiocinfo(struct MPT3SAS_ADAPTER *ioc, void __user *arg)
{
struct mpt3_ioctl_iocinfo karg;
- if (copy_from_user(&karg, arg, sizeof(karg))) {
+ if (!access_ok(VERIFY_READ, arg, sizeof(karg))) {
pr_err("failure at %s:%d/%s()!\n",
__FILE__, __LINE__, __func__);
return -EFAULT;
--
2.7.4
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| From | Christoph Hellwig <hch@infradead.org> |
|---|---|
| Date | 2017-09-20 17:10 +0200 |
| Message-ID | <urONs-4IC-13@gated-at.bofh.it> |
| In reply to | #1735415 |
On Tue, Sep 19, 2017 at 11:11:11PM -0400, Meng Xu wrote: > Since right after the user copy, we are going to > memset(&karg, 0, sizeof(karg)), I guess an access_ok check is enough? The right thing is to remove it entirely.
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| From | Al Viro <viro@ZenIV.linux.org.uk> |
|---|---|
| Date | 2017-09-21 05:30 +0200 |
| Message-ID | <us0lz-3Je-1@gated-at.bofh.it> |
| In reply to | #1735415 |
On Tue, Sep 19, 2017 at 11:11:11PM -0400, Meng Xu wrote: > Since right after the user copy, we are going to > memset(&karg, 0, sizeof(karg)), I guess an access_ok check is enough? access_ok() is *NOT* "will copy_from_user() succeed?" Not even close. On a bunch of architectures (sparc64, for one) access_ok() is always true. All it does is checking that address is not a kernel one - e.g. on i386 anything in range 0..3Gb qualifies. Whether anything's mapped at that address or not. Why bother with that copy_from_user() at all? The same ioctl() proceeds to copy_to_user() on exact same range; all you get from it is "if the area passed by caller is writable, but not readable, fail with -EFAULT". Who cares? Just drop that copy_from_user() completely. Anything access_ok() might've caught will be caught by copy_to_user() anyway.
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| From | Meng Xu <mengxu.gatech@gmail.com> |
|---|---|
| Date | 2017-09-21 05:40 +0200 |
| Message-ID | <us0vf-3MA-1@gated-at.bofh.it> |
| In reply to | #1736342 |
> On Sep 20, 2017, at 11:26 PM, Al Viro <viro@ZenIV.linux.org.uk> wrote: > > On Tue, Sep 19, 2017 at 11:11:11PM -0400, Meng Xu wrote: >> Since right after the user copy, we are going to >> memset(&karg, 0, sizeof(karg)), I guess an access_ok check is enough? > > access_ok() is *NOT* "will copy_from_user() succeed?" Not even close. > On a bunch of architectures (sparc64, for one) access_ok() is always > true. > > All it does is checking that address is not a kernel one - e.g. on > i386 anything in range 0..3Gb qualifies. Whether anything's mapped > at that address or not. > > Why bother with that copy_from_user() at all? The same ioctl() > proceeds to copy_to_user() on exact same range; all you get from > it is "if the area passed by caller is writable, but not readable, > fail with -EFAULT". Who cares? > > Just drop that copy_from_user() completely. Anything access_ok() > might've caught will be caught by copy_to_user() anyway. Yes, Christoph has suggested the same thing and I have submitted another patch with copy_from_user removed entirely.
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