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Message-ID: <ZRxIQF8BHM_woghk@hog> Date: Tue, 3 Oct 2023 18:58:40 +0200 From: Sabrina Dubroca <sd@...asysnail.net> To: "Gustavo A. R. Silva" <gustavoars@...nel.org> Cc: Ayush Sawal <ayush.sawal@...lsio.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Rohit Maheshwari <rohitm@...lsio.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH v2][next] cxgb4/ch_ktls: Fix undefined behavior bug in struct chcr_ktls_ofld_ctx_tx 2023-10-03, 12:56:54 +0200, Gustavo A. R. Silva wrote: > `struct tls_offload_context_tx` is a flexible structure, which means > that it contains a flexible-array member at the bottom. This could > potentially lead to an overwrite of the objects following `base` in > `struct chcr_ktls_ofld_ctx_tx` at run-time. > > Notice that flexible-array member `driver_state` in `struct > tls_offload_context_tx` can grow up to 16 bytes: > > | include/net/tls.h-170: > | #define TLS_DRIVER_STATE_SIZE_TX 16 > > | include/net/tls.h-173: > | #define TLS_OFFLOAD_CONTEXT_SIZE_TX \ > | (sizeof(struct tls_offload_context_tx) + TLS_DRIVER_STATE_SIZE_TX) > > | net/tls/tls_device.c-1119: > | offload_ctx = kzalloc(TLS_OFFLOAD_CONTEXT_SIZE_TX, GFP_KERNEL); > > Fix this by placing the declaration of object `base` at the end of > `struct chcr_ktls_ofld_ctx_tx`. AFAIU, chcr_ktls_ofld_ctx_tx just misuses the extra space allocated by tls_set_device_offload. There's no bug, but the code is a bit confusing. I don't think this patch works, since chcr_ktls doesn't allocate its own memory for chcr_ktls_ofld_ctx_tx. As part of a series of cleanups that I'll submit soon (hopefully this week), I updated chcr_ktls to use the driver_state part of tls_offload_context_tx (instead of the cast in chcr_get_ktls_tx_context), and then removed the flexarrays from tls_offload_context_tx and tls_offload_context_rx (since they're actually a fixed size). -- Sabrina
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