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[69.131.217.18]) by smtp.gmail.com with ESMTPSA id 00721157ae682-79876c40439sm87536317b3.37.2026.03.05.02.24.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Mar 2026 02:24:33 -0800 (PST) Message-ID: Date: Thu, 5 Mar 2026 05:24:29 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Possible newline injection into fdinfo To: Christian Brauner Cc: Linux kernel mailing list , dri-devel@lists.freedesktop.org, linux-fsdevel@vger.kernel.org References: <08f230b4-8c01-45b8-9956-7cfb9f82eeff@gmail.com> <20260304-wertigkeit-rockkonzert-ac7270334804@brauner> <20260305-gespeichert-athletisch-a25f907e6d2a@brauner> Content-Language: en-US From: Demi Marie Obenour Autocrypt: addr=demiobenour@gmail.com; keydata= xsFNBFp+A0oBEADffj6anl9/BHhUSxGTICeVl2tob7hPDdhHNgPR4C8xlYt5q49yB+l2nipd aq+4Gk6FZfqC825TKl7eRpUjMriwle4r3R0ydSIGcy4M6eb0IcxmuPYfbWpr/si88QKgyGSV Z7GeNW1UnzTdhYHuFlk8dBSmB1fzhEYEk0RcJqg4AKoq6/3/UorR+FaSuVwT7rqzGrTlscnT DlPWgRzrQ3jssesI7sZLm82E3pJSgaUoCdCOlL7MMPCJwI8JpPlBedRpe9tfVyfu3euTPLPx wcV3L/cfWPGSL4PofBtB8NUU6QwYiQ9Hzx4xOyn67zW73/G0Q2vPPRst8LBDqlxLjbtx/WLR 6h3nBc3eyuZ+q62HS1pJ5EvUT1vjyJ1ySrqtUXWQ4XlZyoEFUfpJxJoN0A9HCxmHGVckzTRl 5FMWo8TCniHynNXsBtDQbabt7aNEOaAJdE7to0AH3T/Bvwzcp0ZJtBk0EM6YeMLtotUut7h2 Bkg1b//r6bTBswMBXVJ5H44Qf0+eKeUg7whSC9qpYOzzrm7+0r9F5u3qF8ZTx55TJc2g656C 9a1P1MYVysLvkLvS4H+crmxA/i08Tc1h+x9RRvqba4lSzZ6/Tmt60DPM5Sc4R0nSm9BBff0N m0bSNRS8InXdO1Aq3362QKX2NOwcL5YaStwODNyZUqF7izjK4QARAQABzTxEZW1pIE1hcmll IE9iZW5vdXIgKGxvdmVyIG9mIGNvZGluZykgPGRlbWlvYmVub3VyQGdtYWlsLmNvbT7CwXgE EwECACIFAlp+A0oCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJELKItV//nCLBhr8Q AK/xrb4wyi71xII2hkFBpT59ObLN+32FQT7R3lbZRjVFjc6yMUjOb1H/hJVxx+yo5gsSj5LS 9AwggioUSrcUKldfA/PKKai2mzTlUDxTcF3vKx6iMXKA6AqwAw4B57ZEJoMM6egm57TV19kz PMc879NV2nc6+elaKl+/kbVeD3qvBuEwsTe2Do3HAAdrfUG/j9erwIk6gha/Hp9yZlCnPTX+ VK+xifQqt8RtMqS5R/S8z0msJMI/ajNU03kFjOpqrYziv6OZLJ5cuKb3bZU5aoaRQRDzkFIR 6aqtFLTohTo20QywXwRa39uFaOT/0YMpNyel0kdOszFOykTEGI2u+kja35g9TkH90kkBTG+a EWttIht0Hy6YFmwjcAxisSakBuHnHuMSOiyRQLu43ej2+mDWgItLZ48Mu0C3IG1seeQDjEYP tqvyZ6bGkf2Vj+L6wLoLLIhRZxQOedqArIk/Sb2SzQYuxN44IDRt+3ZcDqsPppoKcxSyd1Ny 2tpvjYJXlfKmOYLhTWs8nwlAlSHX/c/jz/ywwf7eSvGknToo1Y0VpRtoxMaKW1nvH0OeCSVJ itfRP7YbiRVc2aNqWPCSgtqHAuVraBRbAFLKh9d2rKFB3BmynTUpc1BQLJP8+D5oNyb8Ts4x Xd3iV/uD8JLGJfYZIR7oGWFLP4uZ3tkneDfYzsFNBFp+A0oBEAC9ynZI9LU+uJkMeEJeJyQ/ 8VFkCJQPQZEsIGzOTlPnwvVna0AS86n2Z+rK7R/usYs5iJCZ55/JISWd8xD57ue0eB47bcJv VqGlObI2DEG8TwaW0O0duRhDgzMEL4t1KdRAepIESBEA/iPpI4gfUbVEIEQuqdqQyO4GAe+M kD0Hy5JH/0qgFmbaSegNTdQg5iqYjRZ3ttiswalql1/iSyv1WYeC1OAs+2BLOAT2NEggSiVO txEfgewsQtCWi8H1SoirakIfo45Hz0tk/Ad9ZWh2PvOGt97Ka85o4TLJxgJJqGEnqcFUZnJJ riwoaRIS8N2C8/nEM53jb1sH0gYddMU3QxY7dYNLIUrRKQeNkF30dK7V6JRH7pleRlf+wQcN fRAIUrNlatj9TxwivQrKnC9aIFFHEy/0mAgtrQShcMRmMgVlRoOA5B8RTulRLCmkafvwuhs6 dCxN0GNAORIVVFxjx9Vn7OqYPgwiofZ6SbEl0hgPyWBQvE85klFLZLoj7p+joDY1XNQztmfA rnJ9x+YV4igjWImINAZSlmEcYtd+xy3Li/8oeYDAqrsnrOjb+WvGhCykJk4urBog2LNtcyCj kTs7F+WeXGUo0NDhbd3Z6AyFfqeF7uJ3D5hlpX2nI9no/ugPrrTVoVZAgrrnNz0iZG2DVx46 x913pVKHl5mlYQARAQABwsFfBBgBAgAJBQJafgNKAhsMAAoJELKItV//nCLBwNIP/AiIHE8b oIqReFQyaMzxq6lE4YZCZNj65B/nkDOvodSiwfwjjVVE2V3iEzxMHbgyTCGA67+Bo/d5aQGj gn0TPtsGzelyQHipaUzEyrsceUGWYoKXYyVWKEfyh0cDfnd9diAm3VeNqchtcMpoehETH8fr RHnJdBcjf112PzQSdKC6kqU0Q196c4Vp5HDOQfNiDnTf7gZSj0BraHOByy9LEDCLhQiCmr+2 E0rW4tBtDAn2HkT9uf32ZGqJCn1O+2uVfFhGu6vPE5qkqrbSE8TG+03H8ecU2q50zgHWPdHM OBvy3EhzfAh2VmOSTcRK+tSUe/u3wdLRDPwv/DTzGI36Kgky9MsDC5gpIwNbOJP2G/q1wT1o Gkw4IXfWv2ufWiXqJ+k7HEi2N1sree7Dy9KBCqb+ca1vFhYPDJfhP75I/VnzHVssZ/rYZ9+5 1yDoUABoNdJNSGUYl+Yh9Pw9pE3Kt4EFzUlFZWbE4xKL/NPno+z4J9aWemLLszcYz/u3XnbO vUSQHSrmfOzX3cV4yfmjM5lewgSstoxGyTx2M8enslgdXhPthZlDnTnOT+C+OTsh8+m5tos8 HQjaPM01MKBiAqdPgksm1wu2DrrwUi6ChRVTUBcj6+/9IJ81H2P2gJk3Ls3AVIxIffLoY34E +MYSfkEjBz0E8CLOcAw7JIwAaeBT In-Reply-To: <20260305-gespeichert-athletisch-a25f907e6d2a@brauner> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------n0M2BcLZOyATHSHw9q6dTRxJ" X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --------------n0M2BcLZOyATHSHw9q6dTRxJ Content-Type: multipart/mixed; boundary="------------lVi0E6f1OjaY0ox5ab0470rF"; protected-headers="v1" Message-ID: Date: Thu, 5 Mar 2026 05:24:29 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Possible newline injection into fdinfo To: Christian Brauner Cc: Linux kernel mailing list , dri-devel@lists.freedesktop.org, linux-fsdevel@vger.kernel.org References: <08f230b4-8c01-45b8-9956-7cfb9f82eeff@gmail.com> <20260304-wertigkeit-rockkonzert-ac7270334804@brauner> <20260305-gespeichert-athletisch-a25f907e6d2a@brauner> Content-Language: en-US From: Demi Marie Obenour Autocrypt: addr=demiobenour@gmail.com; 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boundary="------------3c037rjh1pCyvaLIQDAIPb3a" --------------3c037rjh1pCyvaLIQDAIPb3a Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 3/5/26 03:34, Christian Brauner wrote: > On Wed, Mar 04, 2026 at 01:57:31PM -0500, Demi Marie Obenour wrote: >> On 3/4/26 08:03, Christian Brauner wrote: >>> On Wed, Mar 04, 2026 at 01:53:42AM -0500, Demi Marie Obenour wrote: >>>> I noticed potentially missing input sanitization in dma_buf_set_name= (), >>>> which is reachable from DMA_BUF_SET_NAME. This allows inserting a n= ame >>>> containing a newline, which is then used to construct the contents o= f >>>> /proc/PID/task/TID/fdinfo/FD. This could confuse userspace programs= >>>> that access this data, possibly tricking them into thinking a file >>>> descriptor is of a different type than it actually is. >>>> >>>> Other code might have similar bugs. For instance, there is code tha= t >>>> uses a sysfs path, a driver name, or a device name from /dev. It is= >>>> possible to sanitize the first, and the second and third should come= >>>> from trusted sources within the kernel itself. The last area where >>>> I found a potential problem is BPF. I don't know if this can happen= =2E >>>> >>>> I think this should be fixed by either sanitizing data on write >>>> (by limiting the allowed characters in dma_buf_set_name()), on read >>>> (by using one of the formats that escapes special characters), or bo= th. >>>> >>>> Is there a better way to identify that a file descriptor is of >>>> a particular type, such as an eventfd? fdinfo is subject to >>> >>> The problem is that most of the anonymous inodes share a single >>> anonymous inode so any uapi that returns information based inode->i_o= p >>> is not going to be usable. >>> >>>> bugs of this type, which might happen again. readlink() reports >>>> "anon_inode:[eventfd]" and S_IFMT reports a mode of 0, but but my >>> >>> That is definitely uapi by now. We've tried to change S_IFMT and it >>> breaks lsfd and other tools so we can't reasonably change it. In fact= , >>> pidfds pretend to be anon_inode even though they're not simply becaus= e >>> some tools parse that out. >> >> Does Linux guarantee that anything that is not an anonymous inode >> will have (st_mode & S_IFMT) !=3D 0? >=20 > Ignoring bugs or disk corruption anonymous inodes should be the only > inode type that has a zero type. Everything else should have a non-zero= > type and the I made the VFS splat in may_open(): >=20 > switch (inode->i_mode & S_IFMT) { > case S_IFLNK: > return -ELOOP; > case S_IFDIR: > if (acc_mode & MAY_WRITE) > return -EISDIR; > if (acc_mode & MAY_EXEC) > return -EACCES; > break; > case S_IFBLK: > case S_IFCHR: > if (!may_open_dev(path)) > return -EACCES; > fallthrough; > case S_IFIFO: > case S_IFSOCK: > if (acc_mode & MAY_EXEC) > return -EACCES; > flag &=3D ~O_TRUNC; > break; > case S_IFREG: > if ((acc_mode & MAY_EXEC) && path_noexec(path)) > return -EACCES; > break; > default: > VFS_BUG_ON_INODE(!IS_ANON_FILE(inode), inode); > } >=20 >> Maybe it is time for a prctl that disables this legacy behavior? >=20 > I've switched anonymous inodes internally to S_IFREG a while ago in [1]= > and then masked it off for userspace. Even just the internal conversion= > caused various subsystems like io_uring to lose it which is why we > reverted it in [2]. >=20 > So any next attempt needs to ensure that there are no internal and no > external regressions. And no prctl()s please. It's a strong contender > for Linux' main landfill next to procfs. > Ideally we'd just look at lsfd and lsof and move them away from any typ= e > assertions. I have asked them to do that for pidfds a while ago and the= y > have merged a patch to that effect.> > [1]: cfd86ef7e8e7 ("anon_inode: = use a proper mode internally") > [2]: 1e7ab6f67824 ("anon_inode: rework assertions") What should programs like that be doing instead, given the fdinfo newline injection bug? Even if the current drivers are fixed, the interface makes it very easy to mess up new ones. It's like preventing XSS when one has to manually HTML-escape everything. 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