On 5/19/2025 12:11 PM, David Howells wrote:
Fix a number of ownership checks made by the VFS that assume that inode->i_uid is meaningful with respect to the UID space of the system performing the check. Network filesystems, however, may violate this assumption - and, indeed, a network filesystem may not even have an actual concept of a UNIX integer UID (cifs, for example).There are a number of places within the VFS where UID checks are made and some of these should be deferring the interpretation to the filesystem by way of the previously added vfs_inode_is_owned_by_me() and vfs_inodes_have_same_owner(): (*) chown_ok() (*) chgrp_ok() These should call vfs_inode_is_owned_by_me(). Possibly these need to defer all their checks to the network filesystem as the interpretation of the new UID/GID depends on the netfs too, but the ->setattr() method gets a chance to deal with that. (*) do_coredump() Should probably call vfs_is_owned_by_me() to check that the file created is owned by the caller - but the check that's there might be sufficient. (*) inode_owner_or_capable() Should call vfs_is_owned_by_me(). I'm not sure whether the namespace mapping makes sense in such a case, but it probably could be used. (*) vfs_setlease() Should call vfs_is_owned_by_me(). Actually, it should query if leasing is permitted. Also, setting locks could perhaps do with a permission call to the filesystem driver as AFS, for example, has a lock permission bit in the ACL, but since the AFS server checks that when the RPC call is made, it's probably unnecessary. (*) acl_permission_check() (*) posix_acl_permission() These functions are only used by generic_permission() which is overridden if ->permission() is supplied, and when evaluating a POSIX ACL, it should arguably be checking the UID anyway. AFS, for example, implements its own ACLs and evaluates them in ->permission() and on the server. (*) may_follow_link() Should call vfs_is_owned_by_me() and also vfs_have_same_owner() on the the link and its parent dir. The latter only applies on world-writable sticky dirs. (*) may_create_in_sticky() The initial subject of this patch. Should call vfs_is_owned_by_me() and also vfs_have_same_owner() both. (*) __check_sticky() Should call vfs_is_owned_by_me() on both the dir and the inode. (*) may_dedupe_file() Should call vfs_is_owned_by_me(). (*) IMA policy ops. I'm not sure what the best way to deal with this is - if, indeed, it needs any changes. Note that wrapping stuff up into vfs_inode_is_owned_by_me() isn't necessarily the most efficient as it means we may end up doing the uid idmapping an extra time - though mostly this is in places where I'm not sure it matters so much. Signed-off-by: David Howells <dhowe...@redhat.com> cc: Etienne Champetier <champetier.etie...@gmail.com> cc: Marc Dionne <marc.dio...@auristor.com> cc: Jeffrey Altman <jalt...@auristor.com> cc: Chet Ramey <chet.ra...@case.edu> cc: Cheyenne Wills <cwi...@sinenomine.net> cc: Alexander Viro <v...@zeniv.linux.org.uk> cc: Christian Brauner <brau...@kernel.org> cc: Steve French <sfre...@samba.org> cc: Mimi Zohar <zo...@linux.ibm.com> cc: linux-...@lists.infradead.org cc: openafs-devel@openafs.org cc: linux-c...@vger.kernel.org cc: linux-fsde...@vger.kernel.org cc: linux-integr...@vger.kernel.org Link: https://groups.google.com/g/gnu.bash.bug/c/6PPTfOgFdL4/m/2AQU-S1N76UJ Link: https://git.savannah.gnu.org/cgit/bash.git/tree/redir.c?h=bash-5.3-rc1#n733 --- fs/attr.c | 58 +++++++++++++++++++++++++++++------------------- fs/coredump.c | 3 +-- fs/inode.c | 8 +++++-- fs/locks.c | 7 ++++-- fs/namei.c | 30 +++++++++++++------------ fs/remap_range.c | 20 +++++++++-------- 6 files changed, 74 insertions(+), 52 deletions(-) diff --git a/fs/attr.c b/fs/attr.c index 9caf63d20d03..fefd92af56a2 100644 --- a/fs/attr.c +++ b/fs/attr.c @@ -16,6 +16,7 @@ #include <linux/fcntl.h> #include <linux/filelock.h> #include <linux/security.h> +#include "internal.h"/*** setattr_should_drop_sgid - determine whether the setgid bit needs to be @@ -91,19 +92,21 @@ EXPORT_SYMBOL(setattr_should_drop_suidgid); * permissions. On non-idmapped mounts or if permission checking is to be * performed on the raw inode simply pass @nop_mnt_idmap. */ -static bool chown_ok(struct mnt_idmap *idmap, - const struct inode *inode, vfsuid_t ia_vfsuid) +static int chown_ok(struct mnt_idmap *idmap, + const struct inode *inode, vfsuid_t ia_vfsuid) { vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode); - if (vfsuid_eq_kuid(vfsuid, current_fsuid()) && - vfsuid_eq(ia_vfsuid, vfsuid)) - return true; + int ret; + + ret = vfs_inode_is_owned_by_me(idmap, inode); + if (ret <= 0) + return ret; if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN)) - return true; + return 0; if (!vfsuid_valid(vfsuid) && ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN)) - return true; - return false; + return 0; + return -EPERM; }/**@@ -118,23 +121,27 @@ static bool chown_ok(struct mnt_idmap *idmap, * permissions. On non-idmapped mounts or if permission checking is to be * performed on the raw inode simply pass @nop_mnt_idmap. */ -static bool chgrp_ok(struct mnt_idmap *idmap, - const struct inode *inode, vfsgid_t ia_vfsgid) +static int chgrp_ok(struct mnt_idmap *idmap, + const struct inode *inode, vfsgid_t ia_vfsgid) { vfsgid_t vfsgid = i_gid_into_vfsgid(idmap, inode); - vfsuid_t vfsuid = i_uid_into_vfsuid(idmap, inode); - if (vfsuid_eq_kuid(vfsuid, current_fsuid())) { + int ret; + + ret = vfs_inode_is_owned_by_me(idmap, inode); + if (ret < 0) + return ret; + if (ret == 0) { if (vfsgid_eq(ia_vfsgid, vfsgid)) - return true; + return 0; if (vfsgid_in_group_p(ia_vfsgid)) - return true; + return 0; } if (capable_wrt_inode_uidgid(idmap, inode, CAP_CHOWN)) - return true; + return 0; if (!vfsgid_valid(vfsgid) && ns_capable(inode->i_sb->s_user_ns, CAP_CHOWN)) - return true; - return false; + return 0; + return -EPERM; }/**@@ -163,6 +170,7 @@ int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry, { struct inode *inode = d_inode(dentry); unsigned int ia_valid = attr->ia_valid; + int ret;/** First check size constraints. These can't be overriden using @@ -179,14 +187,18 @@ int setattr_prepare(struct mnt_idmap *idmap, struct dentry *dentry, goto kill_priv;/* Make sure a caller can chown. */- if ((ia_valid & ATTR_UID) && - !chown_ok(idmap, inode, attr->ia_vfsuid)) - return -EPERM; + if (ia_valid & ATTR_UID) { + ret = chown_ok(idmap, inode, attr->ia_vfsuid); + if (ret < 0) + return ret; + }/* Make sure caller can chgrp. */- if ((ia_valid & ATTR_GID) && - !chgrp_ok(idmap, inode, attr->ia_vfsgid)) - return -EPERM; + if (ia_valid & ATTR_GID) { + ret = chgrp_ok(idmap, inode, attr->ia_vfsgid); + if (ret < 0) + return ret; + }/* Make sure a caller can chmod. */if (ia_valid & ATTR_MODE) { diff --git a/fs/coredump.c b/fs/coredump.c index c33c177a701b..ded3936b2067 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -720,8 +720,7 @@ void do_coredump(const kernel_siginfo_t *siginfo) * filesystem. */ idmap = file_mnt_idmap(cprm.file); - if (!vfsuid_eq_kuid(i_uid_into_vfsuid(idmap, inode), - current_fsuid())) { + if (vfs_inode_is_owned_by_me(idmap, inode) != 0) { coredump_report_failure("Core dump to %s aborted: " "cannot preserve file owner", cn.corename); goto close_fail; diff --git a/fs/inode.c b/fs/inode.c index 99318b157a9a..7e91b6f87757 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -2586,11 +2586,15 @@ bool inode_owner_or_capable(struct mnt_idmap *idmap, { vfsuid_t vfsuid; struct user_namespace *ns; + int ret;- vfsuid = i_uid_into_vfsuid(idmap, inode);- if (vfsuid_eq_kuid(vfsuid, current_fsuid())) + ret = vfs_inode_is_owned_by_me(idmap, inode); + if (ret == 0) return true; + if (ret < 0) + return false;+ vfsuid = i_uid_into_vfsuid(idmap, inode);ns = current_user_ns(); if (vfsuid_has_mapping(ns, vfsuid) && ns_capable(ns, CAP_FOWNER)) return true; diff --git a/fs/locks.c b/fs/locks.c index 1619cddfa7a4..b7a2a3ab7529 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -68,6 +68,7 @@ #include <trace/events/filelock.h>#include <linux/uaccess.h>+#include "internal.h"static struct file_lock *file_lock(struct file_lock_core *flc){ @@ -2013,10 +2014,12 @@ int vfs_setlease(struct file *filp, int arg, struct file_lease **lease, void **priv) { struct inode *inode = file_inode(filp); - vfsuid_t vfsuid = i_uid_into_vfsuid(file_mnt_idmap(filp), inode); int error;- if ((!vfsuid_eq_kuid(vfsuid, current_fsuid())) && !capable(CAP_LEASE))+ error = vfs_inode_is_owned_by_me(file_mnt_idmap(filp), inode); + if (error < 0) + return error; + if (error != 0 && !capable(CAP_LEASE)) return -EACCES; if (!S_ISREG(inode->i_mode)) return -EINVAL; diff --git a/fs/namei.c b/fs/namei.c index 9f42dc46322f..6ede952d424a 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1195,26 +1195,26 @@ static int vfs_inodes_have_same_owner(struct mnt_idmap *idmap, struct inode *ino * * Returns 0 if following the symlink is allowed, -ve on error. */ -static inline int may_follow_link(struct nameidata *nd, const struct inode *inode) +static inline int may_follow_link(struct nameidata *nd, struct inode *inode) { struct mnt_idmap *idmap; - vfsuid_t vfsuid; + int ret;if (!sysctl_protected_symlinks)return 0;- idmap = mnt_idmap(nd->path.mnt);- vfsuid = i_uid_into_vfsuid(idmap, inode); - /* Allowed if owner and follower match. */ - if (vfsuid_eq_kuid(vfsuid, current_fsuid())) - return 0; - /* Allowed if parent directory not sticky and world-writable. */ if ((nd->dir_mode & (S_ISVTX|S_IWOTH)) != (S_ISVTX|S_IWOTH)) return 0;+ idmap = mnt_idmap(nd->path.mnt);+ /* Allowed if owner and follower match. */ + ret = vfs_inode_is_owned_by_me(idmap, inode); + if (ret <= 0) + return ret; + /* Allowed if parent directory and link owner match. */ - if (vfsuid_valid(nd->dir_vfsuid) && vfsuid_eq(nd->dir_vfsuid, vfsuid)) + if (vfs_inodes_have_same_owner(idmap, inode, nd)) return 0;if (nd->flags & LOOKUP_RCU)@@ -3157,12 +3157,14 @@ EXPORT_SYMBOL(user_path_at); int __check_sticky(struct mnt_idmap *idmap, struct inode *dir, struct inode *inode) { - kuid_t fsuid = current_fsuid(); + int ret;- if (vfsuid_eq_kuid(i_uid_into_vfsuid(idmap, inode), fsuid))- return 0; - if (vfsuid_eq_kuid(i_uid_into_vfsuid(idmap, dir), fsuid)) - return 0; + ret = vfs_inode_is_owned_by_me(idmap, inode); + if (ret <= 0) + return ret; + ret = vfs_inode_is_owned_by_me(idmap, dir); + if (ret <= 0) + return ret; return !capable_wrt_inode_uidgid(idmap, inode, CAP_FOWNER); } EXPORT_SYMBOL(__check_sticky); diff --git a/fs/remap_range.c b/fs/remap_range.c index 26afbbbfb10c..9eee93c27001 100644 --- a/fs/remap_range.c +++ b/fs/remap_range.c @@ -413,20 +413,22 @@ loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in, EXPORT_SYMBOL(vfs_clone_file_range);/* Check whether we are allowed to dedupe the destination file */-static bool may_dedupe_file(struct file *file) +static int may_dedupe_file(struct file *file) { struct mnt_idmap *idmap = file_mnt_idmap(file); struct inode *inode = file_inode(file); + int ret;if (capable(CAP_SYS_ADMIN))- return true; + return 0; if (file->f_mode & FMODE_WRITE) - return true; - if (vfsuid_eq_kuid(i_uid_into_vfsuid(idmap, inode), current_fsuid())) - return true; + return 0; + ret = vfs_inode_is_owned_by_me(idmap, inode); + if (ret <= 0) + return ret; if (!inode_permission(idmap, inode, MAY_WRITE)) - return true; - return false; + return 0; + return -EPERM; }loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos,@@ -459,8 +461,8 @@ loff_t vfs_dedupe_file_range_one(struct file *src_file, loff_t src_pos, if (ret) return ret;- ret = -EPERM;- if (!may_dedupe_file(dst_file)) + ret = may_dedupe_file(dst_file); + if (ret < 0) goto out_drop_write;ret = -EXDEV;
Reviewed-by: Jeffrey Altman <jalt...@auristor.com>This change looks good to me. It should be noted that it assumes that filesystem specific is_owned_by_me inode_operation can properly handle all inode types. The preceding change will need a fix for the afs implementation.
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