From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in
vm_table") fixes underflow value setting risk in vm_table but misses
vdso_enabled sysctl.
vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
avoid negative value writes but the proc_handler is proc_dointvec and not
proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
The following command thus works :
`# echo -1 > /proc/sys/vm/vdso_enabled`
This patch properly sets the proc_handler to proc_dointvec_minmax.
Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
---
kernel/sysctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 79e6cb1d5c48f..37b1c1a760985 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2194,7 +2194,7 @@ static struct ctl_table vm_table[] = {
.maxlen = sizeof(vdso_enabled),
#endif
.mode = 0644,
- .proc_handler = proc_dointvec,
+ .proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ZERO,
},
#endif
--
2.47.0On Thu, Nov 14, 2024 at 05:25:51PM +0100, nicolas.bouchinet@clip-os.org wrote:
> From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>
> Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in
> vm_table") fixes underflow value setting risk in vm_table but misses
> vdso_enabled sysctl.
>
> vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
> avoid negative value writes but the proc_handler is proc_dointvec and not
> proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
>
> The following command thus works :
>
> `# echo -1 > /proc/sys/vm/vdso_enabled`
It would be interesting to know what happens when you do a
# echo (INT_MAX + 1) > /proc/sys/vm/vdso_enabled
This is the reasons why I'm interested in such a test:
1. Both proc_dointvec and proc_dointvec_minmax (calls proc_dointvec) have a
overflow check where they will return -EINVAL if what is given by the user is
greater than (unsiged long)INT_MAX; this will evaluate can evaluate to true
or false depending on the architecture where we are running.
2. I noticed that vdso_enabled is an unsigned long. And so the expectation is
that the range is 0 to ULONG_MAX, which in some cases (depending on the arch)
would not be the case.
So my question is: What is the expected range for this value? Because you might
not be getting the whole range in the cases where int is 32 bit and long is 64
bit.
>
> This patch properly sets the proc_handler to proc_dointvec_minmax.
>
> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
> ---
> kernel/sysctl.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 79e6cb1d5c48f..37b1c1a760985 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -2194,7 +2194,7 @@ static struct ctl_table vm_table[] = {
> .maxlen = sizeof(vdso_enabled),
> #endif
> .mode = 0644,
> - .proc_handler = proc_dointvec,
> + .proc_handler = proc_dointvec_minmax,
> .extra1 = SYSCTL_ZERO,
Any reason why extra2 is not defined. I know that it was not defined before, but
this does not mean that it will not have an upper limit. The way that I read the
situation is that this will be bounded by the overflow check done in
proc_dointvec and will have an upper limit of INT_MAX.
Please correct me if I have read the situation incorrectly.
Best
--
Joel Granados
Hi Joel,
I've pushed patchset version 3 :
https://lore.kernel.org/all/20241217132908.38096-1-nicolas.bouchinet@clip-os.org/.
On 11/20/24 13:53, Joel Granados wrote:
> On Thu, Nov 14, 2024 at 05:25:51PM +0100, nicolas.bouchinet@clip-os.org wrote:
>> From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>>
>> Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in
>> vm_table") fixes underflow value setting risk in vm_table but misses
>> vdso_enabled sysctl.
>>
>> vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
>> avoid negative value writes but the proc_handler is proc_dointvec and not
>> proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
>>
>> The following command thus works :
>>
>> `# echo -1 > /proc/sys/vm/vdso_enabled`
> It would be interesting to know what happens when you do a
> # echo (INT_MAX + 1) > /proc/sys/vm/vdso_enabled
>
> This is the reasons why I'm interested in such a test:
>
> 1. Both proc_dointvec and proc_dointvec_minmax (calls proc_dointvec) have a
> overflow check where they will return -EINVAL if what is given by the user is
> greater than (unsiged long)INT_MAX; this will evaluate can evaluate to true
> or false depending on the architecture where we are running.
>
> 2. I noticed that vdso_enabled is an unsigned long. And so the expectation is
> that the range is 0 to ULONG_MAX, which in some cases (depending on the arch)
> would not be the case.
From my observations, vdso_enabled is a unsigned int. If one wants to
convert to an unsigned long, proc_doulongvec_minmax should be used
instead.
IMHO, the main issues are that .data variable type can differ from the
return
type of .proc_handler function. This can lead to undefined behaviors and
eventually vulnerabilities.
.extra1 and .extra2 can also be used with proc_handlers that do not uses
them.
I think sysctl_check_table() could be enhanced to control this behavior.
>
> So my question is: What is the expected range for this value? Because you might
> not be getting the whole range in the cases where int is 32 bit and long is 64
> bit.
If proc_dointvec or its derivative is used, as you said, range is bounded
by checks in do_proc_dointvec_conv ((unsigned long) INT_MAX).
INT_MAX being based on the max value of an int (((int)(~0U >> 1))),
do_proc_dointvec_conv behavior is thus architecture dependent.
>
>> This patch properly sets the proc_handler to proc_dointvec_minmax.
>>
>> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
>> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>> ---
>> kernel/sysctl.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 79e6cb1d5c48f..37b1c1a760985 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -2194,7 +2194,7 @@ static struct ctl_table vm_table[] = {
>> .maxlen = sizeof(vdso_enabled),
>> #endif
>> .mode = 0644,
>> - .proc_handler = proc_dointvec,
>> + .proc_handler = proc_dointvec_minmax,
>> .extra1 = SYSCTL_ZERO,
> Any reason why extra2 is not defined. I know that it was not defined before, but
> this does not mean that it will not have an upper limit. The way that I read the
> situation is that this will be bounded by the overflow check done in
> proc_dointvec and will have an upper limit of INT_MAX.
I've added an extra2 parameter to restrict vdso_enabled between 0 and 1
in patchset v3.
https://lore.kernel.org/all/20241217132908.38096-3-nicolas.bouchinet@clip-os.org/
>
> Please correct me if I have read the situation incorrectly.
>
> Best
>
Thanks again for your review,
Best regards,
Nicolas
On Tue, Dec 17, 2024 at 02:57:51PM +0100, Nicolas Bouchinet wrote:
> Hi Joel,
>
> I've pushed patchset version 3 :
> https://lore.kernel.org/all/20241217132908.38096-1-nicolas.bouchinet@clip-os.org/.
>
> On 11/20/24 13:53, Joel Granados wrote:
> > On Thu, Nov 14, 2024 at 05:25:51PM +0100, nicolas.bouchinet@clip-os.org wrote:
> >> From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
> >>
> >> Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in
> >> vm_table") fixes underflow value setting risk in vm_table but misses
> >> vdso_enabled sysctl.
> >>
> >> vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
> >> avoid negative value writes but the proc_handler is proc_dointvec and not
> >> proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
> >>
> >> The following command thus works :
> >>
> >> `# echo -1 > /proc/sys/vm/vdso_enabled`
> > It would be interesting to know what happens when you do a
> > # echo (INT_MAX + 1) > /proc/sys/vm/vdso_enabled
> >
> > This is the reasons why I'm interested in such a test:
> >
> > 1. Both proc_dointvec and proc_dointvec_minmax (calls proc_dointvec) have a
> > overflow check where they will return -EINVAL if what is given by the user is
> > greater than (unsiged long)INT_MAX; this will evaluate can evaluate to true
> > or false depending on the architecture where we are running.
> >
> > 2. I noticed that vdso_enabled is an unsigned long. And so the expectation is
> > that the range is 0 to ULONG_MAX, which in some cases (depending on the arch)
> > would not be the case.
> From my observations, vdso_enabled is a unsigned int. If one wants to
> convert to an unsigned long, proc_doulongvec_minmax should be used
> instead.
Yep, 100% agree, I miss-read and commented incorrectly. Just ignore my
previous comment; I don't know what I was smoking...
>
> IMHO, the main issues are that .data variable type can differ from the
> return type of .proc_handler function. This can lead to undefined
> behaviors and eventually vulnerabilities.
I totally agree that it can lead to unexpected behavior. Would have to
look at a specific case to see if it is really "undefined".
>
> .extra1 and .extra2 can also be used with proc_handlers that do not
> uses them.
In this case they are just silently ignored. Leading the developer to
believe that they are range checked, when they are really not.
> I think sysctl_check_table() could be enhanced to control
> this behavior.
This might be the case. I can review a proposal if you send it out.
Best
--
Joel Granados
Hi Joel,
Thank's for your reply.
I apologize for the reply delay, I wasn't available late weeks.
On 11/20/24 1:53 PM, Joel Granados wrote:
> On Thu, Nov 14, 2024 at 05:25:51PM +0100, nicolas.bouchinet@clip-os.org wrote:
>> From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>>
>> Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in
>> vm_table") fixes underflow value setting risk in vm_table but misses
>> vdso_enabled sysctl.
>>
>> vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
>> avoid negative value writes but the proc_handler is proc_dointvec and not
>> proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
>>
>> The following command thus works :
>>
>> `# echo -1 > /proc/sys/vm/vdso_enabled`
> It would be interesting to know what happens when you do a
> # echo (INT_MAX + 1) > /proc/sys/vm/vdso_enabled
Great question, I'll check that.
>
> This is the reasons why I'm interested in such a test:
>
> 1. Both proc_dointvec and proc_dointvec_minmax (calls proc_dointvec) have a
> overflow check where they will return -EINVAL if what is given by the user is
> greater than (unsiged long)INT_MAX; this will evaluate can evaluate to true
> or false depending on the architecture where we are running.
Indeed, I'll run tests to avouch behaviors of proc handlers bound checks
with
different architectures.
>
> 2. I noticed that vdso_enabled is an unsigned long. And so the expectation is
> that the range is 0 to ULONG_MAX, which in some cases (depending on the arch)
> would not be the case.
Yep, it is. As I've tried to explain in the cover letter
(https://lore.kernel.org/all/20241112131357.49582-1-nicolas.bouchinet@clip-os.org/),
there are numerous places where sysctl data type differs from the proc
handler
return type.
AFAIK, for proc_dointvec there is more than 10 different sysctl where it
happens. The three I've patched represents three common mistakes using
proc_handlers.
>
> So my question is: What is the expected range for this value? Because you might
> not be getting the whole range in the cases where int is 32 bit and long is 64
> bit.
>
>> This patch properly sets the proc_handler to proc_dointvec_minmax.
>>
>> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
>> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>> ---
>> kernel/sysctl.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>> index 79e6cb1d5c48f..37b1c1a760985 100644
>> --- a/kernel/sysctl.c
>> +++ b/kernel/sysctl.c
>> @@ -2194,7 +2194,7 @@ static struct ctl_table vm_table[] = {
>> .maxlen = sizeof(vdso_enabled),
>> #endif
>> .mode = 0644,
>> - .proc_handler = proc_dointvec,
>> + .proc_handler = proc_dointvec_minmax,
>> .extra1 = SYSCTL_ZERO,
> Any reason why extra2 is not defined. I know that it was not defined before, but
> this does not mean that it will not have an upper limit. The way that I read the
> situation is that this will be bounded by the overflow check done in
> proc_dointvec and will have an upper limit of INT_MAX.
Yes, it is bounded by the overflow checks done in proc_dointvec, I've not
changed the current sysctl behavior but we should bound it between 0
and 1 since it seems vdso compat is not supported anymore since
Commit b0b49f2673f011cad ("x86, vdso: Remove compat vdso support").
This is the behavior of vdso32_enabled exposed under the abi sysctl
node.
>
> Please correct me if I have read the situation incorrectly.
You perfectly understood the problematic of it, thanks a lot for your
review.
I'll reply to above questions after I've run more tests.
I saw GKH already merged the third commit of this patchset and
backported it to stable branches.
Should I evict it from future version of this patchset ?
Thanks,
Nicolas
>
> Best
>
On Tue, Dec 10, 2024 at 03:58:41PM +0100, Nicolas Bouchinet wrote:
> Hi Joel,
>
>
> Thank's for your reply.
>
> I apologize for the reply delay, I wasn't available late weeks.
>
> On 11/20/24 1:53 PM, Joel Granados wrote:
> > On Thu, Nov 14, 2024 at 05:25:51PM +0100, nicolas.bouchinet@clip-os.org wrote:
> >> From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
> >>
> >> Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in
> >> vm_table") fixes underflow value setting risk in vm_table but misses
> >> vdso_enabled sysctl.
> >>
> >> vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
> >> avoid negative value writes but the proc_handler is proc_dointvec and not
> >> proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
> >>
> >> The following command thus works :
> >>
> >> `# echo -1 > /proc/sys/vm/vdso_enabled`
> > It would be interesting to know what happens when you do a
> > # echo (INT_MAX + 1) > /proc/sys/vm/vdso_enabled
>
> Great question, I'll check that.
>
> >
> > This is the reasons why I'm interested in such a test:
> >
> > 1. Both proc_dointvec and proc_dointvec_minmax (calls proc_dointvec) have a
> > overflow check where they will return -EINVAL if what is given by the user is
> > greater than (unsiged long)INT_MAX; this will evaluate can evaluate to true
> > or false depending on the architecture where we are running.
>
> Indeed, I'll run tests to avouch behaviors of proc handlers bound checks
> with
> different architectures.
>
> >
> > 2. I noticed that vdso_enabled is an unsigned long. And so the expectation is
> > that the range is 0 to ULONG_MAX, which in some cases (depending on the arch)
> > would not be the case.
> Yep, it is. As I've tried to explain in the cover letter
> (https://lore.kernel.org/all/20241112131357.49582-1-nicolas.bouchinet@clip-os.org/),
> there are numerous places where sysctl data type differs from the proc
> handler
> return type.
>
> AFAIK, for proc_dointvec there is more than 10 different sysctl where it
> happens. The three I've patched represents three common mistakes using
> proc_handlers.
It would be useful to analyze the others. Do you have more outstanding
patches for these?
>
> >
> > So my question is: What is the expected range for this value? Because you might
> > not be getting the whole range in the cases where int is 32 bit and long is 64
> > bit.
> >
> >> This patch properly sets the proc_handler to proc_dointvec_minmax.
> >>
> >> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
> >> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
> >> ---
> >> kernel/sysctl.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> >> index 79e6cb1d5c48f..37b1c1a760985 100644
> >> --- a/kernel/sysctl.c
> >> +++ b/kernel/sysctl.c
> >> @@ -2194,7 +2194,7 @@ static struct ctl_table vm_table[] = {
> >> .maxlen = sizeof(vdso_enabled),
> >> #endif
> >> .mode = 0644,
> >> - .proc_handler = proc_dointvec,
> >> + .proc_handler = proc_dointvec_minmax,
> >> .extra1 = SYSCTL_ZERO,
> > Any reason why extra2 is not defined. I know that it was not defined before, but
> > this does not mean that it will not have an upper limit. The way that I read the
> > situation is that this will be bounded by the overflow check done in
> > proc_dointvec and will have an upper limit of INT_MAX.
>
> Yes, it is bounded by the overflow checks done in proc_dointvec, I've not
> changed the current sysctl behavior but we should bound it between 0
> and 1 since it seems vdso compat is not supported anymore since
> Commit b0b49f2673f011cad ("x86, vdso: Remove compat vdso support").
I think you have already done this in your V3
>
> This is the behavior of vdso32_enabled exposed under the abi sysctl
> node.
>
> >
> > Please correct me if I have read the situation incorrectly.
> You perfectly understood the problematic of it, thanks a lot for your
> review.
>
> I'll reply to above questions after I've run more tests.
>
> I saw GKH already merged the third commit of this patchset and
> backported it to stable branches.
> Should I evict it from future version of this patchset ?
Yes. You should remove what has already been merged into main
line. thx.
Best
--
Joel Granados
On 12/18/24 14:21, Joel Granados wrote:
> On Tue, Dec 10, 2024 at 03:58:41PM +0100, Nicolas Bouchinet wrote:
>> Hi Joel,
>>
>>
>> Thank's for your reply.
>>
>> I apologize for the reply delay, I wasn't available late weeks.
>>
>> On 11/20/24 1:53 PM, Joel Granados wrote:
>>> On Thu, Nov 14, 2024 at 05:25:51PM +0100, nicolas.bouchinet@clip-os.org wrote:
>>>> From: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>>>>
>>>> Commit 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in
>>>> vm_table") fixes underflow value setting risk in vm_table but misses
>>>> vdso_enabled sysctl.
>>>>
>>>> vdso_enabled sysctl is initialized with .extra1 value as SYSCTL_ZERO to
>>>> avoid negative value writes but the proc_handler is proc_dointvec and not
>>>> proc_dointvec_minmax and thus do not uses .extra1 and .extra2.
>>>>
>>>> The following command thus works :
>>>>
>>>> `# echo -1 > /proc/sys/vm/vdso_enabled`
>>> It would be interesting to know what happens when you do a
>>> # echo (INT_MAX + 1) > /proc/sys/vm/vdso_enabled
>> Great question, I'll check that.
>>
>>> This is the reasons why I'm interested in such a test:
>>>
>>> 1. Both proc_dointvec and proc_dointvec_minmax (calls proc_dointvec) have a
>>> overflow check where they will return -EINVAL if what is given by the user is
>>> greater than (unsiged long)INT_MAX; this will evaluate can evaluate to true
>>> or false depending on the architecture where we are running.
>> Indeed, I'll run tests to avouch behaviors of proc handlers bound checks
>> with
>> different architectures.
>>
>>> 2. I noticed that vdso_enabled is an unsigned long. And so the expectation is
>>> that the range is 0 to ULONG_MAX, which in some cases (depending on the arch)
>>> would not be the case.
>> Yep, it is. As I've tried to explain in the cover letter
>> (https://lore.kernel.org/all/20241112131357.49582-1-nicolas.bouchinet@clip-os.org/),
>> there are numerous places where sysctl data type differs from the proc
>> handler
>> return type.
>>
>> AFAIK, for proc_dointvec there is more than 10 different sysctl where it
>> happens. The three I've patched represents three common mistakes using
>> proc_handlers.
> It would be useful to analyze the others. Do you have more outstanding
> patches for these?
I've started to analyze them more in depth it this monday, will send a
patchset when
it seems ok.
I'm focusing on proc_dointvec for now.
>
>>> So my question is: What is the expected range for this value? Because you might
>>> not be getting the whole range in the cases where int is 32 bit and long is 64
>>> bit.
>>>
>>>> This patch properly sets the proc_handler to proc_dointvec_minmax.
>>>>
>>>> Fixes: 3b3376f222e3 ("sysctl.c: fix underflow value setting risk in vm_table")
>>>> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@ssi.gouv.fr>
>>>> ---
>>>> kernel/sysctl.c | 2 +-
>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
>>>> index 79e6cb1d5c48f..37b1c1a760985 100644
>>>> --- a/kernel/sysctl.c
>>>> +++ b/kernel/sysctl.c
>>>> @@ -2194,7 +2194,7 @@ static struct ctl_table vm_table[] = {
>>>> .maxlen = sizeof(vdso_enabled),
>>>> #endif
>>>> .mode = 0644,
>>>> - .proc_handler = proc_dointvec,
>>>> + .proc_handler = proc_dointvec_minmax,
>>>> .extra1 = SYSCTL_ZERO,
>>> Any reason why extra2 is not defined. I know that it was not defined before, but
>>> this does not mean that it will not have an upper limit. The way that I read the
>>> situation is that this will be bounded by the overflow check done in
>>> proc_dointvec and will have an upper limit of INT_MAX.
>> Yes, it is bounded by the overflow checks done in proc_dointvec, I've not
>> changed the current sysctl behavior but we should bound it between 0
>> and 1 since it seems vdso compat is not supported anymore since
>> Commit b0b49f2673f011cad ("x86, vdso: Remove compat vdso support").
> I think you have already done this in your V3
>
>> This is the behavior of vdso32_enabled exposed under the abi sysctl
>> node.
>>
>>> Please correct me if I have read the situation incorrectly.
>> You perfectly understood the problematic of it, thanks a lot for your
>> review.
>>
>> I'll reply to above questions after I've run more tests.
>>
>> I saw GKH already merged the third commit of this patchset and
>> backported it to stable branches.
>> Should I evict it from future version of this patchset ?
> Yes. You should remove what has already been merged into main
> line. thx.
>
> Best
>
© 2016 - 2026 Red Hat, Inc.