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b=eXXJKrHlfKOnCoUmQEb5dhXKVJl8fGP/nZMYgqqCLwLhBYDlXfVSqSPvNZUMrJ8Hd IsGSOtTUrRWhjqFlVQjwUvm2m21jhZ2n6FOTy1IDEjiUHJTC0jpzq/QnjE4um14A4w 0breH3BvgoX7jO7b/SOKuj1JsinoiC2Km/xiaEUeRUugfSzqaZDcEAEaKl2M2IUvuM 3iYudVdLTUqe8pZtAEjIYj0UPSrlgZ5UCLZDqwRKp1jy+Jgv9AOo3NU+m2aFGEwNWj E8oIoaJV+ixqGnRjOOhBzLjvZbeTPLED57Nwey4Iy9PjoTBcv1Y69Qwlebk9LiUC4J t7zayUKQziegw== From: "David Hildenbrand (Arm)" Date: Wed, 28 Oct 2026 10:55:02 +0100 Subject: [PATCH v3 04/15] mm/shmem: honour F_SEAL_EXEC when an ACL is set X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261028-fixes_shmem-v3-4-4ce3baf2db4b@kernel.org> References: <20261028-fixes_shmem-v3-0-4ce3baf2db4b@kernel.org> In-Reply-To: <20261028-fixes_shmem-v3-0-4ce3baf2db4b@kernel.org> To: Andrew Morton , Gregory Price , Zi Yan , Joshua Hahn , Rakie Kim , Ying Huang , Johannes Weiner , Vladimir Davydov , Michal Hocko , Hugh Dickins , Baolin Wang , Lukas Czerner , Carlos Maiolino , Christian Brauner , Jan Kara , Daniel Verkamp , Jeff Xu , Muchun Song , Oscar Salvador , David Stevens , "Matthew Wilcox (Oracle)" , William Kucharski , Chris Li , Kairui Song , Nhat Pham , Miaohe Lin , Naoya Horiguchi Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, "David Hildenbrand (Arm)" , Chris Mason , stable@vger.kernel.org, Pedro Falcato , "Kiryl Shutsemau (Meta)" , "Pratyush Yadav (Google)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3904; i=david@kernel.org; h=from:subject:message-id; bh=CFNC+JPqed7vXaXG6PNtLhwhDnB9KggNxDs0QNHpGlE=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIeHmucu66t9pe9xq19S5Pa9jPwdUm+0FQV949zzRaNe pMXln64o5SFQYyDQVZMkSUo+L7By5fraqvd+Jhh5rAygQxh4OIUgIl0qTD8dxb96vz2Yd4jGdES s9K58x+YCnkJ6HQdPfG75p+TW//3U4wMOzfyK0w78CLl5MXVGbJKqctXHJCatd3GXZr5h/+M97E 6TAA= X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: BD47440008 X-Stat-Signature: y89t7779uxknqh34swo98w1t9xompxwe 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=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793181355-628166 X-HE-Meta: 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 LBgT9fXk 1QxQQhR9Och6/wT6xzdZwpuw+HSNXhVK7dZMKNmd4dofl+c6a2dhLQ+6GD/4x5G6q//9/LJfQeQEQ5TUDjn9DHmI/fbNLNRRjtkV3HxIAs4z+IvCcAJOb/HyfhvdASUo5SPPyG/SL+fFBJn3eSw33q+N8aAR/htP/zJVKIreSyu5Pjx7b1VBS1AQeGzYmIesAbr0UaTQhIh/OmHId6snY7lXWX8o40GZBoudRSzn05X8+RoSm9kJk/yBSxBmsMj73fSR5YkL/fovyWOkT7qA4GW3QClJbrPXRjuxgJ7A8wyrjQ7Tbqtw3B5VFHLeB37pyiW1Js0CrXbb286HpNJO8dfwtmEkw0nhCtleoh3we3ep3ITDX8rayy3lS2r/YQ+zya1uNP90tLXWsENDOcg8l7rEAsvZCQIvjTZL5KhdAXgRzlIenHUgCoA5kdzuAkVObZr6irWR0sbO+1gq+8aptmwHVhg== 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 From: Chris Mason The owner of a memfd sealed with F_SEAL_EXEC can still change its execute bits by setting a POSIX access ACL. With CONFIG_TMPFS_POSIX_ACL, this lets an unprivileged owner make a non-executable memfd executable, bypassing vm.memfd_noexec=2. simple_set_acl() updates i_mode directly, bypassing the seal check in shmem_setattr(). Add shmem_set_acl() to check the resulting mode. Share the F_SEAL_EXEC check with shmem_setattr() using memfd_check_seals_mode() in include/linux/memfd.h. Fix generated by an LLM and sent by Chris Mason in private. Fixes: 6fd7353829ca ("mm/memfd: add F_SEAL_EXEC") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason Acked-by: Pedro Falcato Acked-by: Kiryl Shutsemau (Meta) Acked-by: Zi Yan Reviewed-by: Baolin Wang Reviewed-by: Pratyush Yadav (Google) Tested-by: Gregory Price (Meta) [ david: use common helper; simplify description ] Signed-off-by: David Hildenbrand (Arm) --- include/linux/memfd.h | 9 +++++++++ mm/shmem.c | 35 ++++++++++++++++++++++++++++++----- 2 files changed, 39 insertions(+), 5 deletions(-) diff --git a/include/linux/memfd.h b/include/linux/memfd.h index c159e40e3f34..272479317cf1 100644 --- a/include/linux/memfd.h +++ b/include/linux/memfd.h @@ -2,10 +2,19 @@ #ifndef __LINUX_MEMFD_H #define __LINUX_MEMFD_H +#include #include #define MEMFD_ANON_NAME "[memfd]" +static inline int memfd_check_seals_mode(unsigned int seals, umode_t old_mode, + umode_t new_mode) +{ + if ((seals & F_SEAL_EXEC) && ((old_mode ^ new_mode) & 0111)) + return -EPERM; + return 0; +} + #ifdef CONFIG_MEMFD_CREATE extern long memfd_fcntl(struct file *file, unsigned int cmd, unsigned int arg); struct folio *memfd_alloc_folio(struct file *memfd, pgoff_t idx); diff --git a/mm/shmem.c b/mm/shmem.c index af21a89abb0f..e3e4bbbe1d80 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -77,6 +77,7 @@ static struct vfsmount *shm_mnt __ro_after_init; #include #include #include +#include #include #include #include @@ -1546,10 +1547,11 @@ static int shmem_setattr(const struct mnt_idmap *idmap, if (error) return error; - if ((info->seals & F_SEAL_EXEC) && (attr->ia_valid & ATTR_MODE)) { - if ((inode->i_mode ^ attr->ia_mode) & 0111) { - return -EPERM; - } + if (attr->ia_valid & ATTR_MODE) { + error = memfd_check_seals_mode(info->seals, inode->i_mode, + attr->ia_mode); + if (error) + return error; } if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) { @@ -5404,12 +5406,35 @@ static const struct file_operations shmem_file_operations = { #endif }; +#ifdef CONFIG_TMPFS_POSIX_ACL +static int shmem_set_acl(const struct mnt_idmap *idmap, struct dentry *dentry, + struct posix_acl *acl, int type) +{ + struct inode *inode = d_inode(dentry); + umode_t mode = inode->i_mode; + int error; + + if (type == ACL_TYPE_ACCESS) { + error = posix_acl_equiv_mode(acl, &mode); + if (error < 0) + return error; + error = memfd_check_seals_mode(SHMEM_I(inode)->seals, + inode->i_mode, mode); + if (error) + return error; + } + return simple_set_acl(idmap, dentry, acl, type); +} +#else +#define shmem_set_acl NULL +#endif + static const struct inode_operations shmem_inode_operations = { .getattr = shmem_getattr, .setattr = shmem_setattr, #ifdef CONFIG_TMPFS_XATTR .listxattr = shmem_listxattr, - .set_acl = simple_set_acl, + .set_acl = shmem_set_acl, .fileattr_get = shmem_fileattr_get, .fileattr_set = shmem_fileattr_set, #endif -- 2.43.0