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b=Ncu9DfiraLPRvKYf9kIaxfvp9YfD75C18sih8ao/6wCR9R9vSlJTBFBm9GdvKGokr m/aayADpprvj20FDNqr5t8oeXaEFiwRgwug9HCS5lSBNB3Txi2XYK2ZRw0eFg+YbZI 0LqcD1hd4crcaN/sD6MfHbAYNef4emqvR9G2c5ClaXbyl5vwKMllJll/Iazr3Sb1dP QEy9qMqyWl1TLeLfi1Q1+Wln7fdiH+YluiW66Nragd6QEu7WfhBciIBgWro9tyI5aM kHQmXhXZOHLEIkZIOqUz3clJqx5v6ccce5a71r1rcHPaJLK37oYnLmGSlZFSwUwleP UiHbVtxm7v04w== Message-ID: Date: Wed, 28 Oct 2026 21:37:27 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 04/15] mm/shmem: honour F_SEAL_EXEC when an ACL is set To: Balbir Singh Cc: 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 , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Chris Mason , stable@vger.kernel.org, Pedro Falcato , "Kiryl Shutsemau (Meta)" , "Pratyush Yadav (Google)" References: <20261028-fixes_shmem-v3-0-4ce3baf2db4b@kernel.org> <20261028-fixes_shmem-v3-4-4ce3baf2db4b@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0042514000D X-Stat-Signature: upgr85yxp3b8a7ewqhzk4bmkzqzo4i8o X-Rspamd-Server: rspam06 X-Spam-Status: No, score=-17.3 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_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793219858-398387 X-HE-Meta: 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 +HZKZZUe 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 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 On 10/28/26 11:06, Balbir Singh wrote: > On Wed, Oct 28, 2026 at 10:55:02AM +0100, David Hildenbrand (Arm) wrote: >> 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, > > If CONFIG_TMPFS_POSIX_ACL is not defined, do we want to set the set_acl > callback to NULL? Earlier it was simple_set_acl Excellent question: because simple_set_acl is NULL for !CONFIG_FS_POSIX_ACL. It's clearer to jsut keep using shmem_set_acl here, thanks! -- Cheers, David