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b=BK+KiVzDxrtkhyhQ9wpPL3KqiL59QI8rrmqxkfIVPVTiccFG9IQLBF2fdvYHpYqdp y0DAETWL4FPrzsIpvR1luJp7o9bw0LZHYODQeQGS1g3bfbhJQMi187UyGn/H/SMkok oUow0TpUJYJyockrcQoaD39KB+LgwtRn3QiuN/SIgKMNs/lmBnHgFC+g4YHtbg4eHJ FZ5l8y59skSPDWCS5Xjo9Dgs7AoNn1UwSb6/JiNfDv0G71SH0oJlmq//EftXBOfvoM UgKXfLDwXdSdYwT8a3TN3zQ7iwMjAoOL8IsoAj18hgjVi2w282Z2czi4Yk0vcyiVDx CyfaRrn3j5G2g== Date: Sun, 1 Dec 2024 19:37:22 +0100 From: Christian Brauner To: Linus Torvalds Cc: Kees Cook , Al Viro , Zbigniew =?utf-8?Q?J=C4=99drzejewski-Szmek?= , Tycho Andersen , Aleksa Sarai , Eric Biederman , Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] exec: fix up /proc/pid/comm in the execveat(AT_EMPTY_PATH) case Message-ID: <20241201-seerosen-opern-8dfda1f79c50@brauner> References: <20241130045437.work.390-kees@kernel.org> <20241130-ohnegleichen-unweigerlich-ce3b8af0fa45@brauner> <20241201-konglomerat-genial-c1344842c88b@brauner> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 6C6B741213 X-Rspam-User: X-Stat-Signature: kh1qo8xrk4yt8scizis4czmb4zs6of7k X-HE-Tag: 1733078240-509265 X-HE-Meta: U2FsdGVkX1/lLB6fd6cRafcpjp+ld9t4jNrkoGCjiwLVrhOh34LRzgZLw+jULBRhdRpgNEDm6Bm76UW1jyQPlE+8/X18zeMEu/dAbK//VLvnHskzJyj3jvH4M3dQS1xT5qzSOjUIa5LJKNxxAXwccr0xW2MREPOlddCyzl4xBJN8bg3V4peqXgzA8vjCTvfD1HwsdDAlOpOUDhmiFCtCU47PaFVnlXq/ehy6le41+6RyVTk17+R0aPKaJ6ujzefMcFbHvjPo5wDi2OyH4tMA4JLw07e/YEnPj8iYhXJQViq0PUx4WkQ/bCFsFehvoa4LBQQnuCeQI+iM0knu1WrK/eZNRMHH3ldd4cSBgQHI/fSyLx0/fTY8DFDD5o6yHnMk5NEz2M4JITPU7/lZJ4YXuEbGqcBBvBPg09xWq0O2o81VCBtL0NygY+zDSM6B8AbgVgl13gig0Pi8u/Vg8bLSabag6yhGG9XVIcUdioOxHUoGKcahg31am4+1torQ5O5Bs8PEOvwxGxLLMSDugq9uesFLuRaT5B7UrIp3FFNSZW/dXxpTx4YOFi/bRJ1cUMKzT6GKRxxg+L2S555F8+UeXtnzrNBGA57yAQTsiTb0nE2D+Hw3nHkGXmn2jLwhEZ162fRbQRQPKe/zc2GucrN1OFOByt7HTX+f9pJOspcZtvfmx7QkGpnwDARx/S96FxyRL0z26RZejbVWMKjVfUFBb8CrkwAMVbUi2EXf6uqePtQ2RBJx/z80C3TxsXQsz9bdnnaFWBQPC0Ng6h2XtyGoZ0mMdSdeKGKaqv5a6ODItT2Ew6LntLRw7s5uhKGYsEMcLbmuZKHKR1qN6HBzKYjkuoQVqDrCPJelRHUEfDQO0xyTDeJF8rWpn6R+QGqMBne29B7OffQtOQeBI9hphRkFhtJHUcOmulNLXmlBsbotO+r+Ejhs9/B7sdZozYuZEMLbaXhdfZLzsGpRV0RtSHS YZG+s+xb uH6d3gEJjxIEYhCLLwILwptLQWVAmQrfJY18aWUftReaw3ipE/pQgIXs73XiQbAZbnqT1hldV+4rlPwyd4iGvEb9UkXv3hN+r8DUCBzrXGsrEIIUMdSTzP1CvePJ5wqmEdRdyltKmvpou/rlJlIi5jvzSYOHxg2DKEi1EuFfb8vwOst09pTA0Xr2GJCfCrPFvm3FsBU9tSjLXcHUudPdCYuJEXLcHYIvjkzxwL48wiSLmW6KcJuplnaGTIR+aK7H+e+ECmg6Ndoa8r7iCjjh0mGprBRmDe16ox6GW20r62JKuS+eP3ol6N6Ee8KfWHa89MNJbFcnTdlSOS98IHIHge+lYsOQml3CsNkB4jAomRBZJko7qKjAtd/nRt/KA1EWv0zPVRzq6F/1vcgg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Dec 01, 2024 at 08:54:41AM -0800, Linus Torvalds wrote: > On Sun, 1 Dec 2024 at 06:17, Christian Brauner wrote: > > > > /* > > * Hold rcu lock to keep the name from being freed behind our back. > > * Use cquire semantics to make sure the terminating NUL from > > * __d_alloc() is seen. > > * > > * Note, we're deliberately sloppy here. We don't need to care about > > * detecting a concurrent rename and just want a sensible name. > > */ > > Sure. Note that even "sensible" isn't truly guaranteed in theory, > since a concurrent rename could be doing a "memcpy()" into the > dentry->d_name.name area at the same time on another CPU. Yeah, I saw, if the dname.name assignment is reorded to happen before the memcpy() afaict. Anyway, it's not that important especially since PR_SET_MM_MAP puts comm, auxv etc. fully under user control anyway.