Re: [PATCH 4.19 00/95] 4.19.209-rc1 review

[Shuah Khan]

On 10/4/21 1:49 PM, Shuah Khan wrote:
> On 10/4/21 11:44 AM, Eric Dumazet wrote:
> > On Mon, Oct 4, 2021 at 10:40 AM Naresh Kamboju
> > <naresh.kamboju@xxxxxxxxxx> wrote:
> > > On Mon, 4 Oct 2021 at 18:32, Greg Kroah-Hartman
> > > <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > > > This is the start of the stable review cycle for the 4.19.209 release.
> > > > There are 95 patches in this series, all will be posted as a response
> > > > to this one.  If anyone has any issues with these being applied, please
> > > > let me know.
> > > >
> > > > Responses should be made by Wed, 06 Oct 2021 12:50:17 +0000.
> > > > Anything received after that time might be too late.
> > > >
> > > > The whole patch series can be found in one patch at:
> > > >          https://www.kernel.org/pub/linux/kernel/v4.x/stable-review/patch-4.19.209-rc1.gz
> > > > or in the git tree and branch at:
> > > >          git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-4.19.y
> > > > and the diffstat can be found below.
> > > >
> > > > thanks,
> > > >
> > > > greg k-h
> > >
> > > Regression found on arm, arm64, i386 and x86.
> > > following kernel crash reported on stable-rc linux-4.19.y.
> >
> > Stable teams should backport cred: allow get_cred() and put_cred() to
> > be given NULL.
> >
> > f06bc03339ad4c1baa964a5f0606247ac1c3c50b
> >
> > Or they should have tweaked my patch before backporting it.
> Seeing the same problem on my test system as well.
>
> Patch applied with fuzz. Didn't need any tweaks. Compiling now.
> Will let you know soon.

With f06bc03339ad4c1baa964a5f0606247ac1c3c50b

Compiled and booted on my test system. No dmesg regressions.

Tested-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>

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diff --git a/include/linux/cred.h b/include/linux/cred.h
index 1dc351d8548b..4b081e4911c8 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -240,7 +240,7 @@ static inline struct cred *get_new_cred(struct cred *cred)
  * @cred: The credentials to reference
  *
  * Get a reference on the specified set of credentials.  The caller must
- * release the reference.
+ * release the reference.  If %NULL is passed, it is returned with no action.
  *
  * This is used to deal with a committed set of credentials.  Although the
  * pointer is const, this will temporarily discard the const and increment the
@@ -251,6 +251,8 @@ static inline struct cred *get_new_cred(struct cred *cred)
 static inline const struct cred *get_cred(const struct cred *cred)
 {
        struct cred *nonconst_cred = (struct cred *) cred;
+       if (!cred)
+               return cred;
        validate_creds(cred);
        nonconst_cred->non_rcu = 0;
        return get_new_cred(nonconst_cred);
@@ -261,7 +263,7 @@ static inline const struct cred *get_cred(const struct cred *cred)
  * @cred: The credentials to release
  *
  * Release a reference to a set of credentials, deleting them when the last ref
- * is released.
+ * is released.  If %NULL is passed, nothing is done.
  *
  * This takes a const pointer to a set of credentials because the credentials
  * on task_struct are attached by const pointers to prevent accidental
@@ -271,9 +273,11 @@ static inline void put_cred(const struct cred *_cred)
 {
        struct cred *cred = (struct cred *) _cred;
 
-       validate_creds(cred);
-       if (atomic_dec_and_test(&(cred)->usage))
-               __put_cred(cred);
+       if (cred) {
+               validate_creds(cred);
+               if (atomic_dec_and_test(&(cred)->usage))
+                       __put_cred(cred);
+       }
 }
 
 /**

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thanks,
-- Shuah