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    SubjectRe: [PATCH] selinux: Add __GFP_NOWARN to allocation at str_read()
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    On 09/13/2018 08:26 AM, Tetsuo Handa wrote:
    > On 2018/09/13 12:02, Paul Moore wrote:
    >> On Fri, Sep 7, 2018 at 12:43 PM Tetsuo Handa
    >> <penguin-kernel@i-love.sakura.ne.jp> wrote:
    >>> syzbot is hitting warning at str_read() [1] because len parameter can
    >>> become larger than KMALLOC_MAX_SIZE. We don't need to emit warning for
    >>> this case.
    >>>
    >>> [1] https://syzkaller.appspot.com/bug?id=7f2f5aad79ea8663c296a2eedb81978401a908f0
    >>>
    >>> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    >>> Reported-by: syzbot <syzbot+ac488b9811036cea7ea0@syzkaller.appspotmail.com>
    >>> ---
    >>> security/selinux/ss/policydb.c | 2 +-
    >>> 1 file changed, 1 insertion(+), 1 deletion(-)
    >>>
    >>> diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
    >>> index e9394e7..f4eadd3 100644
    >>> --- a/security/selinux/ss/policydb.c
    >>> +++ b/security/selinux/ss/policydb.c
    >>> @@ -1101,7 +1101,7 @@ static int str_read(char **strp, gfp_t flags, void *fp, u32 len)
    >>> if ((len == 0) || (len == (u32)-1))
    >>> return -EINVAL;
    >>>
    >>> - str = kmalloc(len + 1, flags);
    >>> + str = kmalloc(len + 1, flags | __GFP_NOWARN);
    >>> if (!str)
    >>> return -ENOMEM;
    >> Thanks for the patch.
    >>
    >> My eyes are starting to glaze over a bit chasing down all of the
    >> different kmalloc() code paths trying to ensure that this always does
    >> the right thing based on size of the allocation and the different slab
    >> allocators ... are we sure that this will always return NULL when (len
    >> + 1) is greater than KMALLOC_MAX_SIZE for the different slab allocator
    >> configurations?
    >>
    > Yes, for (len + 1) cannot become 0 (which causes kmalloc() to return
    > ZERO_SIZE_PTR) due to (len == (u32)-1) check above.
    >
    > The only concern would be whether you want allocation failure messages.
    > I assumed you don't need it because we are returning -ENOMEM to the caller.
    >
    Would it not be better with

        char *str;

        if ((len == 0) || (len == (u32)-1) || (len >= KMALLOC_MAX_SIZE))
            return -EINVAL;

        str = kmalloc(len + 1, flags);
        if (!str)
            return -ENOMEM;

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