| Message ID | 20180321134247.GA1275@embeddedgus (mailing list archive) |
|---|---|
| State | Rejected |
| Delegated to: | Johannes Berg |
| Headers | show |
On 03/21/2018 08:48 AM, Johannes Berg wrote: > On Wed, 2018-03-21 at 08:42 -0500, Gustavo A. R. Silva wrote: >> In preparation to enabling -Wvla, remove VLAs and replace them >> with dynamic memory allocation instead. >> >> The use of stack Variable Length Arrays needs to be avoided, as they >> can be a vector for stack exhaustion, which can be both a runtime bug >> or a security flaw. Also, in general, as code evolves it is easy to >> lose track of how big a VLA can get. Thus, we can end up having runtime >> failures that are hard to debug. >> >> Also, fixed as part of the directive to remove all VLAs from >> the kernel: https://lkml.org/lkml/2018/3/7/621 >> >> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> >> --- >> net/mac80211/aes_cmac.c | 36 ++++++++++++++++++++++++------------ >> 1 file changed, 24 insertions(+), 12 deletions(-) >> >> diff --git a/net/mac80211/aes_cmac.c b/net/mac80211/aes_cmac.c >> index 2fb6558..c9444bf 100644 >> --- a/net/mac80211/aes_cmac.c >> +++ b/net/mac80211/aes_cmac.c >> @@ -27,30 +27,42 @@ static const u8 zero[CMAC_TLEN_256]; >> void ieee80211_aes_cmac(struct crypto_shash *tfm, const u8 *aad, >> const u8 *data, size_t data_len, u8 *mic) >> { >> - SHASH_DESC_ON_STACK(desc, tfm); >> + struct shash_desc *shash; >> u8 out[AES_BLOCK_SIZE]; >> >> - desc->tfm = tfm; >> + shash = kmalloc(sizeof(*shash) + crypto_shash_descsize(tfm), >> + GFP_KERNEL); >> + if (!shash) >> + return; > > Honestly, this seems like a really bad idea - you're now hitting > kmalloc for every TX/RX frame here. > > SHA_DESC_ON_STACK() should just be fixed to not need a VLA, but take > some sort of maximum, I guess? > SHA_DESC_ON_STACK is currently being used in multiple places. But, yeah, I think we can define multiple macros of the same kind and adjust to the characteristics of each the component. How big do you think tfm can get? Thanks -- Gustavo
On 03/21/2018 08:58 AM, Johannes Berg wrote: > On Wed, 2018-03-21 at 08:57 -0500, Gustavo A. R. Silva wrote: >> >> SHA_DESC_ON_STACK is currently being used in multiple places. But, yeah, >> I think we can define multiple macros of the same kind and adjust to the >> characteristics of each the component. >> >> How big do you think tfm can get? > > I have no idea, I guess you'll have to take that with Herbert. > > johannes > I see. I'll contact him then. Thanks for the feedback. -- Gustavo
diff --git a/net/mac80211/aes_cmac.c b/net/mac80211/aes_cmac.c index 2fb6558..c9444bf 100644 --- a/net/mac80211/aes_cmac.c +++ b/net/mac80211/aes_cmac.c @@ -27,30 +27,42 @@ static const u8 zero[CMAC_TLEN_256]; void ieee80211_aes_cmac(struct crypto_shash *tfm, const u8 *aad, const u8 *data, size_t data_len, u8 *mic) { - SHASH_DESC_ON_STACK(desc, tfm); + struct shash_desc *shash; u8 out[AES_BLOCK_SIZE]; - desc->tfm = tfm; + shash = kmalloc(sizeof(*shash) + crypto_shash_descsize(tfm), + GFP_KERNEL); + if (!shash) + return; - crypto_shash_init(desc); - crypto_shash_update(desc, aad, AAD_LEN); - crypto_shash_update(desc, data, data_len - CMAC_TLEN); - crypto_shash_finup(desc, zero, CMAC_TLEN, out); + shash->tfm = tfm; + + crypto_shash_init(shash); + crypto_shash_update(shash, aad, AAD_LEN); + crypto_shash_update(shash, data, data_len - CMAC_TLEN); + crypto_shash_finup(shash, zero, CMAC_TLEN, out); memcpy(mic, out, CMAC_TLEN); + kfree(shash); } void ieee80211_aes_cmac_256(struct crypto_shash *tfm, const u8 *aad, const u8 *data, size_t data_len, u8 *mic) { - SHASH_DESC_ON_STACK(desc, tfm); + struct shash_desc *shash; + + shash = kmalloc(sizeof(*shash) + crypto_shash_descsize(tfm), + GFP_KERNEL); + if (!shash) + return; - desc->tfm = tfm; + shash->tfm = tfm; - crypto_shash_init(desc); - crypto_shash_update(desc, aad, AAD_LEN); - crypto_shash_update(desc, data, data_len - CMAC_TLEN_256); - crypto_shash_finup(desc, zero, CMAC_TLEN_256, mic); + crypto_shash_init(shash); + crypto_shash_update(shash, aad, AAD_LEN); + crypto_shash_update(shash, data, data_len - CMAC_TLEN_256); + crypto_shash_finup(shash, zero, CMAC_TLEN_256, mic); + kfree(shash); } struct crypto_shash *ieee80211_aes_cmac_key_setup(const u8 key[],
In preparation to enabling -Wvla, remove VLAs and replace them with dynamic memory allocation instead. The use of stack Variable Length Arrays needs to be avoided, as they can be a vector for stack exhaustion, which can be both a runtime bug or a security flaw. Also, in general, as code evolves it is easy to lose track of how big a VLA can get. Thus, we can end up having runtime failures that are hard to debug. Also, fixed as part of the directive to remove all VLAs from the kernel: https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> --- net/mac80211/aes_cmac.c | 36 ++++++++++++++++++++++++------------ 1 file changed, 24 insertions(+), 12 deletions(-)