From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793007679; b=07JbsXEo4/It6oI25pYQUhE2kC41FzBWwZujPNmieLKNtWFyBIhEXshv2JIl9lze1ozV yajHZAyWYmaL6AyspF/uGSsPbYMW6Lvx79a98yDUXeqGPaZhIjjO33BlxFMkZRp0LlSvx pl70BBTYYSNMZI6aC5dqchHUzfzZRFrZA5dtvabIP0HTwRKrWV/T1ZWWCufN+QukgJ2Fe iDbJuoCTEr9MHMmZbCF9BjbwAgvtvGu+AJLyQwB4Rnb+1nw/5ZrZB8pSFmjHFfzrwe3yr 2F+gtcxwAOFgHD3clU/01V4Ufs6y9TrZGIx7CqNDKrwrMRmCsx/LYa2XcqvJ+FCTZXw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793007679; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=BxRlcgnZgnkhi6+O0aTsbz1x8Tq983dT+cO3SyC2Rpk=; b=5SlvK4f1YHM96u92xH7SQAluSUtJrt3CXURrsZjdIdGIChiP+kSEimU4i477l4s0DfJF iQulBD7L+32wQ8QQXyEZ0uI0cqHyIZ/tL8gX+MPIEir2FK0QmsZVauFmoos9Qqav17u47 XVuQuj4kFK6D2PDLhfW42b4/wYQgW6tlZa9yxn35PcCA4teVb5jqFLpIwvTrRhJ9DiKDq XCJ7MY/RCWcaChDr4Sf9gRf6pvJJ158VM0C9wJQaMVRuUxV2kqE2vO3ve86vlxixNttSC gVKP/7dKewzsNzdJcA31KDA/MMNJIgCofblfjFFNBFKiDcVqz95UXUq9eTowvPOonzQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LLWJfIRf; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 08B7460A260E; Mon, 26 Oct 2026 09:41:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=LLWJfIRf Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0B28E1F01828; Mon, 26 Oct 2026 09:41:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793007678; bh=BxRlcgnZgnkhi6+O0aTsbz1x8Tq983dT+cO3SyC2Rpk=; h=From:Date:Subject:References:In-Reply-To:To:Cc; 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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list 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 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