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SubjectRe: [PATCH] nfs: Don't deref potentially NULL pointer returned by strsep
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On Jul 4, 2011, at 5:04 AM, Jesper Juhl wrote:

> On Sun, 3 Jul 2011, Chuck Lever wrote:
>
>>
>> On Jul 3, 2011, at 3:40 AM, Jesper Juhl wrote:
>>
>>> In fs/nfs/nfsroot.c:root_nfs_parse_options() we call strsep(), which
>>> may return NULL, but we do not test the return value before
>>> dereferencing the pointer.
>>>
>>> Signed-off-by: Jesper Juhl <jj@chaosbits.net>
>>> ---
>>> fs/nfs/nfsroot.c | 2 ++
>>> 1 files changed, 2 insertions(+), 0 deletions(-)
>>>
>>> Compile tested only.
>>>
>>> diff --git a/fs/nfs/nfsroot.c b/fs/nfs/nfsroot.c
>>> index c4744e1..b6ac860 100644
>>> --- a/fs/nfs/nfsroot.c
>>> +++ b/fs/nfs/nfsroot.c
>>> @@ -191,6 +191,8 @@ static int __init root_nfs_parse_options(char *incoming, char *exppath,
>>> * Set the NFS remote path
>>> */
>>> p = strsep(&incoming, ",");
>>> + if (!p)
>>> + return -1;
>>
>> strsep() may return NULL only if the value of "incoming" is NULL. But
>> callers ensure that "incoming" always contains the address of a fixed
>> buffer. Thus if strsep() returns NULL here there is some kind of
>> programming error; it's not the result of invalid input.
>>
>> Do you have a reproducible test case to make this fail?
>>
> Nope. I simply spotted the unchecked strsep() call and thought that it
> would be better to be defensive and check it in case callers change in the
> future and a bug creeps in that causes a NULL incoming to be passed.
> Perhaps a BUG_ON(!incoming) would be better - or perhaps just forget about
> it.

While I personally prefer an explicit assertion in cases like this one, the community preference is to avoid cluttering the code with BUG_ONs, since the code would crash anyway in that case.

--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com





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