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    SubjectRe: [PATCH v3 3/3] KEYS: Use kvmalloc() to better handle large buffer allocation
    On Fri, Mar 13, 2020 at 11:21:02AM -0400, Waiman Long wrote:
    > For large multi-page temporary buffer allocation, the security/keys
    > subsystem don't need contiguous physical pages. It will work perfectly
    > fine with virtually mapped pages.
    >
    > Replace the kmalloc() call by kvmalloc() and provide a __kvzfree()
    > helper function to clear and free the kvmalloc'ed buffer. This will
    > reduce the chance of memory allocation failure just because of highly
    > fragmented pages.
    >
    > Suggested-by: David Howells <dhowells@redhat.com>
    > Signed-off-by: Waiman Long <longman@redhat.com>
    > ---
    > security/keys/internal.h | 14 ++++++++++++++
    > security/keys/keyctl.c | 10 +++++-----
    > 2 files changed, 19 insertions(+), 5 deletions(-)
    >
    > diff --git a/security/keys/internal.h b/security/keys/internal.h
    > index ba3e2da14cef..855b11eb73ee 100644
    > --- a/security/keys/internal.h
    > +++ b/security/keys/internal.h
    > @@ -16,6 +16,8 @@
    > #include <linux/keyctl.h>
    > #include <linux/refcount.h>
    > #include <linux/compat.h>
    > +#include <linux/mm.h>
    > +#include <linux/vmalloc.h>
    >
    > struct iovec;
    >
    > @@ -349,4 +351,16 @@ static inline void key_check(const struct key *key)
    >
    > #endif
    >
    > +/*
    > + * Helper function to clear and free a kvmalloc'ed memory object.
    > + */
    > +static inline void __kvzfree(const void *addr, size_t len)
    > +{
    > + if (is_vmalloc_addr(addr)) {
    > + memset((void *)addr, 0, len);
    > + vfree(addr);
    > + } else {
    > + kzfree(addr);
    > + }
    > +}

    Since this takes the length as a parameter, it can be simplified to:

    static inline void __kvzfree(const void *addr, size_t len)
    {
    if (addr) {
    memset((void *)addr, 0, len);
    kvfree(addr);
    }
    }

    > if (!tmpbuf || unlikely(ret > tmpbuflen)) {
    > if (unlikely(tmpbuf))
    > - kzfree(tmpbuf);
    > + __kvzfree(tmpbuf, tmpbuflen);

    Both kzfree() and __kvzfree() handle a NULL pointer, so there's no need for the
    NULL check first.

    > @@ -920,7 +920,7 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
    > ret = -EFAULT;
    > }
    > if (tmpbuf)
    > - kzfree(tmpbuf);
    > + __kvzfree(tmpbuf, tmpbuflen);

    Likewise here. No need for the NULL check.

    - Eric

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