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b=AOGtv8MfSvpV7/N3SPQdxO34HN0jitae0lUNpVEJDAU9XLw0mdF8nEKatSbYah4D4 pJnFyEpZO1zbMa9uji/9OWzr8wEr6lfii12mf0iU2Lh2VjsLavJMVeCqDZp/52sjZ8 3Go4KV6nkkS39oFoJGSvgQnMVnncUKXYL8Mx162m4aQQqRHIlpeUtyYZQRcyHTHG+m F6SJS7Gx3owS0zf+1GA3KxpXJd3wQWd0E3FPh1GuNLid6UQ0pR28EaGxERe/wN3pMg +vSX7Zm5D1718tOrlyhaV4OrQ07V2BymOcNC4cPME/yryrTT1k2SVGUu6wuwzfR22j +9kSochp+NapA== From: Christian Brauner To: linux-fsdevel@vger.kernel.org Cc: Linus Torvalds , Jann Horn , Josef Bacik , Chris Mason , Jeff Layton , NeilBrown , Eric Dumazet , Thomas Gleixner , Al Viro , Jonathan Corbet , Christoph Hellwig , Greg Kroah-Hartman , Joel Granados , Kees Cook , Jan Kara , Jan Kara , linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, linux-um@lists.infradead.org, linux-wireless@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, ntfs3@lists.linux.dev, platform-driver-x86@vger.kernel.org, coreteam@netfilter.org, kexec@lists.infradead.org, linux-pci@vger.kernel.org, linux-sound@vger.kernel.org, netfilter-devel@vger.kernel.org, dri-devel@lists.freedesktop.org, ibm-acpi-devel@lists.sourceforge.net, jfs-discussion@lists.sourceforge.net, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-cifs@vger.kernel.org, linux-fbdev@vger.kernel.org, linux-hwmon@vger.kernel.org, linux-mm@kvack.org, linux-sh@vger.kernel.org, linux-usb@vger.kernel.org, samba-technical@lists.samba.org, sparclinux@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-doc@vger.kernel.org, linux-serial@vger.kernel.org, linux-atm-general@lists.sourceforge.net, Takashi Iwai , linux-input@vger.kernel.org, linux-raid@vger.kernel.org, linux-ext4@vger.kernel.org, linux-modules@vger.kernel.org, linux-debuggers@vger.kernel.org, "Christian Brauner (Amutable)" , Chuck Lever , stable@vger.kernel.org Subject: [PATCH RESEND v2 36/51] proc: don't let NOMMU map procfs files Date: Wed, 4 Nov 2026 20:24:48 +0100 Message-ID: <20261104-work-procfs-bugfixes-v2-36-021c84d852e0@kernel.org> In-Reply-To: <20261104-work-procfs-bugfixes-v2-0-021c84d852e0@kernel.org> References: <20261104-work-procfs-bugfixes-v2-0-021c84d852e0@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" X-Mailer: b4 0.17-dev X-Developer-Signature: v=1; a=openpgp-sha256; l=3847; i=brauner@kernel.org; h=from:subject:message-id; bh=JTUUxaAv8g+OiylD/jB4kSfUdacg86Bjtrwx1fOwQ90=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWS9bvzxcvsOxp23JLZfCWya6MPaPHGnRYPLhkVvf4fHB W9U5hb431HKwiDGxSArpsji0G4SLrecp2KzUaYGzBxWJpAhDFycAjCRyk+MDK+PBU/le8dv0ftD 839XV15oaNPWrTw8hs1fHTLi/wid+Mbwv6CPOeDfzSePDj+a/VD2SORxlTWdy84uUOARvTIlTdD JgRcA X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Content-Transfer-Encoding: 8bit X-Stat-Signature: sr9sfoddxwxdddoxiwu83ohp4qotazje X-Rspamd-Server: rspam01 X-Rspam-User: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: 35AEFA0003 X-HE-Tag: 1793820303-441517 X-HE-Meta: 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 TyLPJME6 R5mM9Xk6scH8R3UlPfSsdZsGeka1uqvbG+iHl0YYkQXDq6bWQbMTUdrDknjbhQcTNfk7jaRtWueq3v6Ru2VC4vZZx73xtwqctaWTIvw4pJK18iMhmBVEBT/vTsJsV4PVPG4DjWHifkZ8Y6ILoqVDSk6+k5dSzlZJO4UtVVAhaMv60xiVuIguHkDFDqb7xDFNrDjsmelFQEvl84WbLLuWPy2y/34kByRf5WYxF6L3NqjzbVph5whvPIl+sIwhujIHupnMBQmevnZnvqUeh+ltKgVhXl2WDML1JZteInfQYsGynGCO9pDKA8iJ/kH/6tyVpyG9TXFFG5NAuS9C3ey3XIcyvEN+tBRGUSrriFzn8ntZ/BXmurdnGscAalozmlahqGEpgpMqVDLpC7mwm+rCq8aHfBGb1aUlGcafJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Every procfs file has a ->mmap since commit 786d7e1612f0 ("Fix rmmod/read/write races in /proc entries"), whether the entry has a ->proc_mmap or not. On NOMMU validate_mmap_request() takes that to mean the file can be mapped. procfs has no ->mmap_capabilities so a regular file gets NOMMU_MAP_COPY, and a private mapping never calls ->mmap at all. Instead do_mmap() takes nommu_region_sem for writing and do_mmap_private() reads the file into the copy with kernel_read(). Reading /proc/maps takes nommu_region_sem as well: mmap(NULL, 4096, PROT_READ, MAP_PRIVATE, open("/proc/maps", O_RDONLY), 0) do_mmap() // down_write(&nommu_region_sem) -> do_mmap_private() -> kernel_read() -> seq_read_iter() -> nommu_region_list_start() // down_read() The task hangs for good, holding nommu_region_sem and its own mmap_lock, and every mmap(), munmap() and exit after that hangs behind it. /proc/maps is 0444 so any user can do that. Give the procfs files a ->mmap_capabilities on NOMMU that allows nothing. That covers every entry and not just /proc/maps, procfs can't know which entry's read takes nommu_region_sem. Mapping a procfs file then fails with -ENODEV, like mapping a file without ->mmap did before 786d7e1612f0. NOMMU never called ->proc_mmap() for a regular file anyway, procfs never offered NOMMU_MAP_DIRECT. Reported-by: Chris Mason Fixes: 786d7e1612f0 ("Fix rmmod/read/write races in /proc entries") Cc: stable@vger.kernel.org Signed-off-by: Christian Brauner (Amutable) --- fs/proc/inode.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/fs/proc/inode.c b/fs/proc/inode.c index b7634f975d98..9933f03ab9fb 100644 --- a/fs/proc/inode.c +++ b/fs/proc/inode.c @@ -466,6 +466,18 @@ proc_reg_get_unmapped_area(struct file *file, unsigned long orig_addr, return rv; } +#ifndef CONFIG_MMU +/* + * NOMMU never calls ->proc_mmap() for a regular file. It reads the file into + * a private copy instead, with nommu_region_sem held for writing, which + * reading /proc/maps takes as well. Don't map procfs files at all. + */ +static unsigned int proc_reg_mmap_capabilities(struct file *file) +{ + return 0; +} +#endif + static int proc_reg_open(struct inode *inode, struct file *file) { struct proc_dir_entry *pde = PDE(inode); @@ -559,6 +571,9 @@ static const struct file_operations proc_reg_file_ops = { .unlocked_ioctl = proc_reg_unlocked_ioctl, .mmap = proc_reg_mmap, .get_unmapped_area = proc_reg_get_unmapped_area, +#ifndef CONFIG_MMU + .mmap_capabilities = proc_reg_mmap_capabilities, +#endif .open = proc_reg_open, .release = proc_reg_release, }; @@ -572,6 +587,9 @@ static const struct file_operations proc_iter_file_ops = { .unlocked_ioctl = proc_reg_unlocked_ioctl, .mmap = proc_reg_mmap, .get_unmapped_area = proc_reg_get_unmapped_area, +#ifndef CONFIG_MMU + .mmap_capabilities = proc_reg_mmap_capabilities, +#endif .open = proc_reg_open, .release = proc_reg_release, }; @@ -586,6 +604,9 @@ static const struct file_operations proc_reg_file_ops_compat = { .compat_ioctl = proc_reg_compat_ioctl, .mmap = proc_reg_mmap, .get_unmapped_area = proc_reg_get_unmapped_area, +#ifndef CONFIG_MMU + .mmap_capabilities = proc_reg_mmap_capabilities, +#endif .open = proc_reg_open, .release = proc_reg_release, }; @@ -600,6 +621,9 @@ static const struct file_operations proc_iter_file_ops_compat = { .compat_ioctl = proc_reg_compat_ioctl, .mmap = proc_reg_mmap, .get_unmapped_area = proc_reg_get_unmapped_area, +#ifndef CONFIG_MMU + .mmap_capabilities = proc_reg_mmap_capabilities, +#endif .open = proc_reg_open, .release = proc_reg_release, }; -- 2.53.0