* [PATCH] sysctl: Make sure proc handlers can't expose heap memory
@ 2020-05-04 19:08 Kees Cook
2020-05-04 19:59 ` Luis Chamberlain
2020-05-05 5:58 ` Christoph Hellwig
0 siblings, 2 replies; 9+ messages in thread
From: Kees Cook @ 2020-05-04 19:08 UTC (permalink / raw)
To: Christoph Hellwig
Cc: Luis Chamberlain, Iurii Zaikin, Alexey Dobriyan, linux-mm,
linux-fsdevel, linux-kernel
Just as a precaution, make sure that proc handlers don't accidentally
grow "count" beyond the allocated kbuf size.
Signed-off-by: Kees Cook <keescook@chromium.org>
---
This applies to hch's sysctl cleanup tree...
---
fs/proc/proc_sysctl.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 15030784566c..535ab26473af 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
struct inode *inode = file_inode(filp);
struct ctl_table_header *head = grab_header(inode);
struct ctl_table *table = PROC_I(inode)->sysctl_entry;
+ size_t count_max = count;
void *kbuf;
ssize_t error;
@@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
if (!write) {
error = -EFAULT;
+ if (WARN_ON(count > count_max))
+ count = count_max;
if (copy_to_user(ubuf, kbuf, count))
goto out_free_buf;
}
--
2.20.1
--
Kees Cook
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-04 19:08 [PATCH] sysctl: Make sure proc handlers can't expose heap memory Kees Cook
@ 2020-05-04 19:59 ` Luis Chamberlain
2020-05-04 20:32 ` Kees Cook
2020-05-05 5:58 ` Christoph Hellwig
1 sibling, 1 reply; 9+ messages in thread
From: Luis Chamberlain @ 2020-05-04 19:59 UTC (permalink / raw)
To: Kees Cook
Cc: Christoph Hellwig, Iurii Zaikin, Alexey Dobriyan, linux-mm,
linux-fsdevel, linux-kernel
On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote:
> Just as a precaution, make sure that proc handlers don't accidentally
> grow "count" beyond the allocated kbuf size.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> This applies to hch's sysctl cleanup tree...
> ---
> fs/proc/proc_sysctl.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 15030784566c..535ab26473af 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> struct inode *inode = file_inode(filp);
> struct ctl_table_header *head = grab_header(inode);
> struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> + size_t count_max = count;
> void *kbuf;
> ssize_t error;
>
> @@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
>
> if (!write) {
> error = -EFAULT;
> + if (WARN_ON(count > count_max))
> + count = count_max;
That crash a system with panic-on-warn. I don't think we want that?
Luis
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-04 19:59 ` Luis Chamberlain
@ 2020-05-04 20:32 ` Kees Cook
2020-05-04 21:59 ` Luis Chamberlain
0 siblings, 1 reply; 9+ messages in thread
From: Kees Cook @ 2020-05-04 20:32 UTC (permalink / raw)
To: Luis Chamberlain
Cc: Christoph Hellwig, Iurii Zaikin, Alexey Dobriyan, linux-mm,
linux-fsdevel, linux-kernel
On Mon, May 04, 2020 at 07:59:37PM +0000, Luis Chamberlain wrote:
> On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote:
> > Just as a precaution, make sure that proc handlers don't accidentally
> > grow "count" beyond the allocated kbuf size.
> >
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> > This applies to hch's sysctl cleanup tree...
> > ---
> > fs/proc/proc_sysctl.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > index 15030784566c..535ab26473af 100644
> > --- a/fs/proc/proc_sysctl.c
> > +++ b/fs/proc/proc_sysctl.c
> > @@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > struct inode *inode = file_inode(filp);
> > struct ctl_table_header *head = grab_header(inode);
> > struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> > + size_t count_max = count;
> > void *kbuf;
> > ssize_t error;
> >
> > @@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> >
> > if (!write) {
> > error = -EFAULT;
> > + if (WARN_ON(count > count_max))
> > + count = count_max;
>
> That crash a system with panic-on-warn. I don't think we want that?
Eh? None of the handlers should be making this mistake currently and
it's not a mistake that can be controlled from userspace. WARN() is
absolutely what's wanted here: report an impossible situation (and
handle it gracefully for the bulk of users that don't have
panic_on_warn set).
--
Kees Cook
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-04 20:32 ` Kees Cook
@ 2020-05-04 21:59 ` Luis Chamberlain
2020-05-05 6:34 ` Greg KH
0 siblings, 1 reply; 9+ messages in thread
From: Luis Chamberlain @ 2020-05-04 21:59 UTC (permalink / raw)
To: Kees Cook, Greg KH
Cc: Christoph Hellwig, Iurii Zaikin, Alexey Dobriyan, linux-mm,
linux-fsdevel, linux-kernel
On Mon, May 04, 2020 at 01:32:07PM -0700, Kees Cook wrote:
> On Mon, May 04, 2020 at 07:59:37PM +0000, Luis Chamberlain wrote:
> > On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote:
> > > Just as a precaution, make sure that proc handlers don't accidentally
> > > grow "count" beyond the allocated kbuf size.
> > >
> > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > ---
> > > This applies to hch's sysctl cleanup tree...
> > > ---
> > > fs/proc/proc_sysctl.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > > index 15030784566c..535ab26473af 100644
> > > --- a/fs/proc/proc_sysctl.c
> > > +++ b/fs/proc/proc_sysctl.c
> > > @@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > > struct inode *inode = file_inode(filp);
> > > struct ctl_table_header *head = grab_header(inode);
> > > struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> > > + size_t count_max = count;
> > > void *kbuf;
> > > ssize_t error;
> > >
> > > @@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > >
> > > if (!write) {
> > > error = -EFAULT;
> > > + if (WARN_ON(count > count_max))
> > > + count = count_max;
> >
> > That would crash a system with panic-on-warn. I don't think we want that?
>
> Eh? None of the handlers should be making this mistake currently and
> it's not a mistake that can be controlled from userspace. WARN() is
> absolutely what's wanted here: report an impossible situation (and
> handle it gracefully for the bulk of users that don't have
> panic_on_warn set).
Alrighty, Greg are you OK with this type of WARN_ON()? You recently
expressed concerns over its use due to panic-on-warn on another patch.
LUis
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-04 19:08 [PATCH] sysctl: Make sure proc handlers can't expose heap memory Kees Cook
2020-05-04 19:59 ` Luis Chamberlain
@ 2020-05-05 5:58 ` Christoph Hellwig
1 sibling, 0 replies; 9+ messages in thread
From: Christoph Hellwig @ 2020-05-05 5:58 UTC (permalink / raw)
To: Kees Cook
Cc: Christoph Hellwig, Luis Chamberlain, Iurii Zaikin,
Alexey Dobriyan, linux-mm, linux-fsdevel, linux-kernel
On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote:
> Just as a precaution, make sure that proc handlers don't accidentally
> grow "count" beyond the allocated kbuf size.
>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> This applies to hch's sysctl cleanup tree...
This looks ok o me. You should probably add Al to the Cc list as
he has picked up my series into a branch of vfs.git.
Acked-by: Christoph Hellwig <hch@lst.de>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-04 21:59 ` Luis Chamberlain
@ 2020-05-05 6:34 ` Greg KH
2020-05-05 20:41 ` Kees Cook
0 siblings, 1 reply; 9+ messages in thread
From: Greg KH @ 2020-05-05 6:34 UTC (permalink / raw)
To: Luis Chamberlain
Cc: Kees Cook, Christoph Hellwig, Iurii Zaikin, Alexey Dobriyan,
linux-mm, linux-fsdevel, linux-kernel
On Mon, May 04, 2020 at 09:59:03PM +0000, Luis Chamberlain wrote:
> On Mon, May 04, 2020 at 01:32:07PM -0700, Kees Cook wrote:
> > On Mon, May 04, 2020 at 07:59:37PM +0000, Luis Chamberlain wrote:
> > > On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote:
> > > > Just as a precaution, make sure that proc handlers don't accidentally
> > > > grow "count" beyond the allocated kbuf size.
> > > >
> > > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > > ---
> > > > This applies to hch's sysctl cleanup tree...
> > > > ---
> > > > fs/proc/proc_sysctl.c | 3 +++
> > > > 1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > > > index 15030784566c..535ab26473af 100644
> > > > --- a/fs/proc/proc_sysctl.c
> > > > +++ b/fs/proc/proc_sysctl.c
> > > > @@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > > > struct inode *inode = file_inode(filp);
> > > > struct ctl_table_header *head = grab_header(inode);
> > > > struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> > > > + size_t count_max = count;
> > > > void *kbuf;
> > > > ssize_t error;
> > > >
> > > > @@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > > >
> > > > if (!write) {
> > > > error = -EFAULT;
> > > > + if (WARN_ON(count > count_max))
> > > > + count = count_max;
> > >
> > > That would crash a system with panic-on-warn. I don't think we want that?
> >
> > Eh? None of the handlers should be making this mistake currently and
> > it's not a mistake that can be controlled from userspace. WARN() is
> > absolutely what's wanted here: report an impossible situation (and
> > handle it gracefully for the bulk of users that don't have
> > panic_on_warn set).
>
> Alrighty, Greg are you OK with this type of WARN_ON()? You recently
> expressed concerns over its use due to panic-on-warn on another patch.
We should never call WARN() on any path that a user can trigger.
If it is just a "the developer called this api in a foolish way" then we
could use a WARN_ON() to have them realize their mistake, but in my
personal experience, foolish developers don't even notice that kind of
mistake :(
thanks,
greg k-h
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-05 6:34 ` Greg KH
@ 2020-05-05 20:41 ` Kees Cook
2020-05-05 22:03 ` Luis Chamberlain
0 siblings, 1 reply; 9+ messages in thread
From: Kees Cook @ 2020-05-05 20:41 UTC (permalink / raw)
To: Greg KH
Cc: Luis Chamberlain, Christoph Hellwig, Iurii Zaikin,
Alexey Dobriyan, linux-mm, linux-fsdevel, linux-kernel
On Tue, May 05, 2020 at 08:34:41AM +0200, Greg KH wrote:
> On Mon, May 04, 2020 at 09:59:03PM +0000, Luis Chamberlain wrote:
> > On Mon, May 04, 2020 at 01:32:07PM -0700, Kees Cook wrote:
> > > On Mon, May 04, 2020 at 07:59:37PM +0000, Luis Chamberlain wrote:
> > > > On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote:
> > > > > Just as a precaution, make sure that proc handlers don't accidentally
> > > > > grow "count" beyond the allocated kbuf size.
> > > > >
> > > > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > > > ---
> > > > > This applies to hch's sysctl cleanup tree...
> > > > > ---
> > > > > fs/proc/proc_sysctl.c | 3 +++
> > > > > 1 file changed, 3 insertions(+)
> > > > >
> > > > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > > > > index 15030784566c..535ab26473af 100644
> > > > > --- a/fs/proc/proc_sysctl.c
> > > > > +++ b/fs/proc/proc_sysctl.c
> > > > > @@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > > > > struct inode *inode = file_inode(filp);
> > > > > struct ctl_table_header *head = grab_header(inode);
> > > > > struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> > > > > + size_t count_max = count;
> > > > > void *kbuf;
> > > > > ssize_t error;
> > > > >
> > > > > @@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > > > >
> > > > > if (!write) {
> > > > > error = -EFAULT;
> > > > > + if (WARN_ON(count > count_max))
> > > > > + count = count_max;
> > > >
> > > > That would crash a system with panic-on-warn. I don't think we want that?
> > >
> > > Eh? None of the handlers should be making this mistake currently and
> > > it's not a mistake that can be controlled from userspace. WARN() is
> > > absolutely what's wanted here: report an impossible situation (and
> > > handle it gracefully for the bulk of users that don't have
> > > panic_on_warn set).
> >
> > Alrighty, Greg are you OK with this type of WARN_ON()? You recently
> > expressed concerns over its use due to panic-on-warn on another patch.
>
> We should never call WARN() on any path that a user can trigger.
>
> If it is just a "the developer called this api in a foolish way" then we
> could use a WARN_ON() to have them realize their mistake, but in my
> personal experience, foolish developers don't even notice that kind of
> mistake :(
Right -- while it'd be nice if the developer noticed it, it is _usually_
an unsuspecting end user (or fuzzer), in which case we absolutely want a
WARN (and not a BUG![1]) and have the situations handled gracefully, so
it can be reported and fixed.
-Kees
[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#bug-and-bug-on
--
Kees Cook
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-05 20:41 ` Kees Cook
@ 2020-05-05 22:03 ` Luis Chamberlain
2020-05-05 23:23 ` Kees Cook
0 siblings, 1 reply; 9+ messages in thread
From: Luis Chamberlain @ 2020-05-05 22:03 UTC (permalink / raw)
To: Kees Cook
Cc: Greg KH, Christoph Hellwig, Iurii Zaikin, Alexey Dobriyan,
linux-mm, linux-fsdevel, linux-kernel
On Tue, May 05, 2020 at 01:41:44PM -0700, Kees Cook wrote:
> On Tue, May 05, 2020 at 08:34:41AM +0200, Greg KH wrote:
> > On Mon, May 04, 2020 at 09:59:03PM +0000, Luis Chamberlain wrote:
> > > On Mon, May 04, 2020 at 01:32:07PM -0700, Kees Cook wrote:
> > > > On Mon, May 04, 2020 at 07:59:37PM +0000, Luis Chamberlain wrote:
> > > > > On Mon, May 04, 2020 at 12:08:55PM -0700, Kees Cook wrote:
> > > > > > Just as a precaution, make sure that proc handlers don't accidentally
> > > > > > grow "count" beyond the allocated kbuf size.
> > > > > >
> > > > > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > > > > > ---
> > > > > > This applies to hch's sysctl cleanup tree...
> > > > > > ---
> > > > > > fs/proc/proc_sysctl.c | 3 +++
> > > > > > 1 file changed, 3 insertions(+)
> > > > > >
> > > > > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> > > > > > index 15030784566c..535ab26473af 100644
> > > > > > --- a/fs/proc/proc_sysctl.c
> > > > > > +++ b/fs/proc/proc_sysctl.c
> > > > > > @@ -546,6 +546,7 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > > > > > struct inode *inode = file_inode(filp);
> > > > > > struct ctl_table_header *head = grab_header(inode);
> > > > > > struct ctl_table *table = PROC_I(inode)->sysctl_entry;
> > > > > > + size_t count_max = count;
> > > > > > void *kbuf;
> > > > > > ssize_t error;
> > > > > >
> > > > > > @@ -590,6 +591,8 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
> > > > > >
> > > > > > if (!write) {
> > > > > > error = -EFAULT;
> > > > > > + if (WARN_ON(count > count_max))
> > > > > > + count = count_max;
> > > > >
> > > > > That would crash a system with panic-on-warn. I don't think we want that?
> > > >
> > > > Eh? None of the handlers should be making this mistake currently and
> > > > it's not a mistake that can be controlled from userspace. WARN() is
> > > > absolutely what's wanted here: report an impossible situation (and
> > > > handle it gracefully for the bulk of users that don't have
> > > > panic_on_warn set).
> > >
> > > Alrighty, Greg are you OK with this type of WARN_ON()? You recently
> > > expressed concerns over its use due to panic-on-warn on another patch.
> >
> > We should never call WARN() on any path that a user can trigger.
> >
> > If it is just a "the developer called this api in a foolish way" then we
> > could use a WARN_ON() to have them realize their mistake, but in my
> > personal experience, foolish developers don't even notice that kind of
> > mistake :(
>
> Right -- while it'd be nice if the developer noticed it, it is _usually_
> an unsuspecting end user (or fuzzer), in which case we absolutely want a
> WARN (and not a BUG![1]) and have the situations handled gracefully, so
> it can be reported and fixed.
I've been using WARN*() for this exact purpose before, so I am as
surprised as you are bout these concerns. However if we have folks
shipping with panic-on-warn this would be rather detrimental to our
goals.
Greg, are you aware of folks shipping with panic-on-warn on some products?
Luis
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] sysctl: Make sure proc handlers can't expose heap memory
2020-05-05 22:03 ` Luis Chamberlain
@ 2020-05-05 23:23 ` Kees Cook
0 siblings, 0 replies; 9+ messages in thread
From: Kees Cook @ 2020-05-05 23:23 UTC (permalink / raw)
To: Luis Chamberlain
Cc: Greg KH, Christoph Hellwig, Iurii Zaikin, Alexey Dobriyan,
linux-mm, linux-fsdevel, linux-kernel
On Tue, May 05, 2020 at 10:03:27PM +0000, Luis Chamberlain wrote:
> On Tue, May 05, 2020 at 01:41:44PM -0700, Kees Cook wrote:
> > Right -- while it'd be nice if the developer noticed it, it is _usually_
> > an unsuspecting end user (or fuzzer), in which case we absolutely want a
> > WARN (and not a BUG![1]) and have the situations handled gracefully, so
> > it can be reported and fixed.
>
> I've been using WARN*() for this exact purpose before, so I am as
> surprised as you are bout these concerns. However if we have folks
I don't see any mismatch here: it's not user-reachable, which is what
Greg said. WARN is for non-user-reachable "impossible situations". We
want to know if those can be hit (via bad API usage, races, etc). If
it's reachable from userspace, then it can't be a WARN() any more and
needs to be pr_warn().
> shipping with panic-on-warn this would be rather detrimental to our
> goals.
>
> Greg, are you aware of folks shipping with panic-on-warn on some products?
People shipping with panic_on_warn are expecting to panic for WARNs like
this. :P
--
Kees Cook
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2020-05-05 23:23 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
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2020-05-04 19:08 [PATCH] sysctl: Make sure proc handlers can't expose heap memory Kees Cook
2020-05-04 19:59 ` Luis Chamberlain
2020-05-04 20:32 ` Kees Cook
2020-05-04 21:59 ` Luis Chamberlain
2020-05-05 6:34 ` Greg KH
2020-05-05 20:41 ` Kees Cook
2020-05-05 22:03 ` Luis Chamberlain
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2020-05-05 5:58 ` Christoph Hellwig
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