Re: [PATCH v16 06/12] bpf: Add bpf_lookup_*_key() and bpf_key_put() kfuncs

On Tue, 2022-09-06 at 04:43 +0200, Kumar Kartikeya Dwivedi wrote:

On Mon, 5 Sept 2022 at 16:35, Roberto Sassu roberto.sassu@huaweicloud.com wrote:

...

From: Roberto Sassu roberto.sassu@huawei.com

Add the bpf_lookup_user_key(), bpf_lookup_system_key() and bpf_key_put() kfuncs, to respectively search a key with a given key handle serial number and flags, obtain a key from a pre-determined ID defined in include/linux/verification.h, and cleanup.

Introduce system_keyring_id_check() to validate the keyring ID parameter of bpf_lookup_system_key().

Signed-off-by: Roberto Sassu roberto.sassu@huawei.com

With a small nit below, Acked-by: Kumar Kartikeya Dwivedi memxor@gmail.com

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include/linux/bpf.h | 8 +++ include/linux/verification.h | 8 +++ kernel/trace/bpf_trace.c | 135 +++++++++++++++++++++++++++++++++++ 3 files changed, 151 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 9dbd7c3f8929..f3db614aece6 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -2595,4 +2595,12 @@ static inline void bpf_cgroup_atype_get(u32 attach_btf_id, int cgroup_atype) {} static inline void bpf_cgroup_atype_put(int cgroup_atype) {} #endif /* CONFIG_BPF_LSM */

+struct key;

+#ifdef CONFIG_KEYS +struct bpf_key {

•   struct key *key;
  

•   bool has_ref;
  

+}; +#endif /* CONFIG_KEYS */ #endif /* _LINUX_BPF_H */ diff --git a/include/linux/verification.h b/include/linux/verification.h index a655923335ae..f34e50ebcf60 100644 --- a/include/linux/verification.h +++ b/include/linux/verification.h @@ -17,6 +17,14 @@ #define VERIFY_USE_SECONDARY_KEYRING ((struct key *)1UL) #define VERIFY_USE_PLATFORM_KEYRING ((struct key *)2UL)

+static inline int system_keyring_id_check(u64 id) +{

•   if (id > (unsigned long)VERIFY_USE_PLATFORM_KEYRING)
  

•           return -EINVAL;
  

•   return 0;
  

+}

/*

• The use to which an asymmetric key is being put.

*/ diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 68e5cdd24cef..7a7023704ac2 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -20,6 +20,8 @@ #include <linux/fprobe.h> #include <linux/bsearch.h> #include <linux/sort.h> +#include <linux/key.h> +#include <linux/verification.h>

#include <net/bpf_sk_storage.h>

@@ -1181,6 +1183,139 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = { .arg1_type = ARG_PTR_TO_CTX, };

+#ifdef CONFIG_KEYS +__diag_push(); +__diag_ignore_all("-Wmissing-prototypes",

•             "kfuncs which will be used in BPF programs");
  

+/**

• • bpf_lookup_user_key - lookup a key by its serial
• • @serial: key handle serial number
• • @flags: lookup-specific flags
• • Search a key with a given *serial* and the provided *flags*.
• • If found, increment the reference count of the key by one, and
• • return it in the bpf_key structure.
• • The bpf_key structure must be passed to bpf_key_put() when done
• • with it, so that the key reference count is decremented and the
• • bpf_key structure is freed.
• • Permission checks are deferred to the time the key is used by
• • one of the available key-specific kfuncs.
• • Set *flags* with KEY_LOOKUP_CREATE, to attempt creating a

requested

• • special keyring (e.g. session keyring), if it doesn't yet

exist.

• • Set *flags* with KEY_LOOKUP_PARTIAL, to lookup a key without

waiting

• • for the key construction, and to retrieve uninstantiated keys

(keys

• • without data attached to them).
• • Return: a bpf_key pointer with a valid key pointer if the key

is found, a

• •     NULL pointer otherwise.
    

• */

+struct bpf_key *bpf_lookup_user_key(u32 serial, u64 flags) +{

•   key_ref_t key_ref;
  

•   struct bpf_key *bkey;
  

•   if (flags & ~KEY_LOOKUP_ALL)
  

•           return NULL;
  

•   /*
  

•    * Permission check is deferred until the key is used, as
  

the

•    * intent of the caller is unknown here.
  

•    */
  

•   key_ref = lookup_user_key(serial, flags,
  

KEY_DEFER_PERM_CHECK);

•   if (IS_ERR(key_ref))
  

•           return NULL;
  

•   bkey = kmalloc(sizeof(*bkey), GFP_ATOMIC);
  

Since this function (due to lookup_user_key) is sleepable, do we really need GFP_ATOMIC here?

Daniel suggested it for bpf_lookup_system_key(), so that the kfunc does not have to be sleepable. For symmetry, I did the same to bpf_lookup_user_key(). Will switch back to GFP_KERNEL.

Thanks

Roberto