Messages in this thread |  | | Date | Mon, 13 Jan 2025 09:07:09 -0500 | | Subject | Re: [PATCH] nfsd: free nfsd_file by gc after adding it to lru list | | From | Chuck Lever <> |
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Hello!
On 1/12/25 9:59 PM, Li Lingfeng wrote: > In nfsd_file_put, after inserting the nfsd_file into the nfsd_file_lru > list, gc may be triggered in another thread and immediately release this > nfsd_file, which will lead to a UAF when accessing this nfsd_file again.
Do you happen to have a reproducer that can trigger this issue?
> All the places where unhash is done will also perform lru_remove, so there > is no need to do lru_remove separately here. After inserting the nfsd_file > into the nfsd_file_lru list, it can be released by relying on gc. > > Fixes: 4a0e73e635e3 ("NFSD: Leave open files out of the filecache LRU")
The code that is being replaced below was introduced in ac3a2585f018 ("nfsd: rework refcounting in filecache"). This fix won't apply to kernels that have only 4a0e73e635e3 but not ac3a2585f018, for instance.
At the very least we need to add "Cc: stable@vger.kernel.org # v6.2" but I'm not convinced "Fixes: 4a0e73e635e3" is correct.
> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com> > --- > fs/nfsd/filecache.c | 12 ++---------- > 1 file changed, 2 insertions(+), 10 deletions(-) > > diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c > index a1cdba42c4fa..37b65cb1579a 100644 > --- a/fs/nfsd/filecache.c > +++ b/fs/nfsd/filecache.c > @@ -372,18 +372,10 @@ nfsd_file_put(struct nfsd_file *nf) > /* Try to add it to the LRU. If that fails, decrement. */ > if (nfsd_file_lru_add(nf)) { > /* If it's still hashed, we're done */ > - if (test_bit(NFSD_FILE_HASHED, &nf->nf_flags)) { > + if (list_lru_count(&nfsd_file_lru)) > nfsd_file_schedule_laundrette(); > - return; > - }
The above change does not seem to be related to the fix described in the patch description. Can you help me understand why this is needed?
> - /* > - * We're racing with unhashing, so try to remove it from > - * the LRU. If removal fails, then someone else already > - * has our reference. > - */ > - if (!nfsd_file_lru_remove(nf)) > - return; > + return; > } > } > if (refcount_dec_and_test(&nf->nf_ref))
-- Chuck Lever
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