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b=LLWJfIRfqQ9yw9zN8w+tiThnDWMyYGvn4LuqFmaS/+sKhD0RYXGM6ekuLbp5pwye0 GlAFStgMZ4bpa74f1YXxkncoHCET/UQGIsZMpznOcVE3Xmzy+UQDI+uXyspDicU48a RwH9olooA8JB2RwulISypqfyfEg2BuWxr9jC0KFeW6gkQcEvmtEnultg/qf45+imgv xOP2nH//hSvDA7H4Rya9klWucPxS630yCdhbc/J0QCPYiQ7ztrPc2vWIote2d2lKzq n28H/ZOeHflhVLZO1TbpQ0jpRnv49HxVS6FYn+bLcMj+oniKTOECFaDwVDwQK06mDn Q3tzYXHhxZhCg== From: "David Hildenbrand (Arm)" Date: Mon, 26 Oct 2026 10:40:37 +0100 Subject: [PATCH 04/16] 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: <20261026-fixes_shmem-v1-4-703206d5fa0c@kernel.org> References: <20261026-fixes_shmem-v1-0-703206d5fa0c@kernel.org> In-Reply-To: <20261026-fixes_shmem-v1-0-703206d5fa0c@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 X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3607; i=david@kernel.org; h=from:subject:message-id; bh=MTJYg0b2CsxJrcKABZR2LY1h7dDRQY+5hOZR0M8LIUo=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLuK4jVT3O8UbFoGtvb8E/hKj+m79twwzyz9KL69Zhz0 XPUIrbu6ChlYRDjYJAVU2QJCr5v8PLlutpqNz5mmDmsTCBDGLg4BWAih3MY/ocumabo41Zs8b81 98X2SZ2fZJuSGX7/ZC5IXXy4c8ncH/oM/11F0stiO/pbry90a6pbmJ955bLoRzPhPf7JQsqlB4v 6uAE= X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B6A03C0003 X-Stat-Signature: ri5tztn7oo5dow1d4ssndmbxi4mn8374 X-Spam-Status: No, score=-19.1 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-Rspam-User: X-HE-Tag: 1793007679-743235 X-HE-Meta: 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 MA32GHKA pVzyda76NaRq+1YqVYb2CQfIsSFiepq1I47l0hDsrr+CE8VT59Gnd3qF+Jj0G8uTGyltVLc62MzoY50B6TwNl5wZbxx2ByWcmyoMOwtllQ4Y3QQZLmqpz45wDhNUIn7gxiIN8s2NnzAvcuemhBhJWCXA1FmTwv5COuACCyyUFpUwPSanKW/wmemEZRTXyWJxIeP716Gk2gMwlo1SRlDFQ5PqtPnSO0RoicANAK1tsxTQC1yG5Akji7mEar3EgQ1i8D5LK1CLMVPYpxHXnNAf0y39JyB2r14EzI+BhGTLBTCHxNpBxhu79VEq45GA9dffJNt5CaLoFk1rsWy+lx1XnzbU/OHCSLDmddZb6lMzkoXW7yq7NgBRbr3KhTg== 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 [ 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 c159e40e3f34a..272479317cf10 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 d97fc32e7c942..86b9d19f26c7e 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 @@ -1549,10 +1550,11 @@ 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)) { @@ -5400,12 +5402,35 @@ 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