6.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Christian Brauner brauner@kernel.org
commit cfd86ef7e8e7b9e015707e46479a6b1de141eed0 upstream.
This allows the VFS to not trip over anonymous inodes and we can add asserts based on the mode into the vfs. When we report it to userspace we can simply hide the mode to avoid regressions. I've audited all direct callers of alloc_anon_inode() and only secretmen overrides i_mode and i_op inode operations but it already uses a regular file.
Link: https://lore.kernel.org/20250407-work-anon_inode-v1-1-53a44c20d44e@kernel.or... Fixes: af153bb63a336 ("vfs: catch invalid modes in may_open()") Reviewed-by: Jeff Layton jlayton@kernel.org Cc: stable@vger.kernel.org # all LTS kernels Reported-by: syzbot+5d8e79d323a13aa0b248@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67ed3fb3.050a0220.14623d.0009.GAE@google.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/anon_inodes.c | 36 ++++++++++++++++++++++++++++++++++++ fs/internal.h | 3 +++ fs/libfs.c | 8 +++++++- 3 files changed, 46 insertions(+), 1 deletion(-)
--- a/fs/anon_inodes.c +++ b/fs/anon_inodes.c @@ -24,10 +24,44 @@
#include <linux/uaccess.h>
+#include "internal.h" + static struct vfsmount *anon_inode_mnt __ro_after_init; static struct inode *anon_inode_inode __ro_after_init;
/* + * User space expects anonymous inodes to have no file type in st_mode. + * + * In particular, 'lsof' has this legacy logic: + * + * type = s->st_mode & S_IFMT; + * switch (type) { + * ... + * case 0: + * if (!strcmp(p, "anon_inode")) + * Lf->ntype = Ntype = N_ANON_INODE; + * + * to detect our old anon_inode logic. + * + * Rather than mess with our internal sane inode data, just fix it + * up here in getattr() by masking off the format bits. + */ +int anon_inode_getattr(struct mnt_idmap *idmap, const struct path *path, + struct kstat *stat, u32 request_mask, + unsigned int query_flags) +{ + struct inode *inode = d_inode(path->dentry); + + generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat); + stat->mode &= ~S_IFMT; + return 0; +} + +static const struct inode_operations anon_inode_operations = { + .getattr = anon_inode_getattr, +}; + +/* * anon_inodefs_dname() is called from d_path(). */ static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) @@ -66,6 +100,7 @@ static struct inode *anon_inode_make_sec if (IS_ERR(inode)) return inode; inode->i_flags &= ~S_PRIVATE; + inode->i_op = &anon_inode_operations; error = security_inode_init_security_anon(inode, &QSTR(name), context_inode); if (error) { @@ -313,6 +348,7 @@ static int __init anon_inode_init(void) anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); if (IS_ERR(anon_inode_inode)) panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode)); + anon_inode_inode->i_op = &anon_inode_operations;
return 0; } --- a/fs/internal.h +++ b/fs/internal.h @@ -343,3 +343,6 @@ static inline bool path_mounted(const st void file_f_owner_release(struct file *file); bool file_seek_cur_needs_f_lock(struct file *file); int statmount_mnt_idmap(struct mnt_idmap *idmap, struct seq_file *seq, bool uid_map); +int anon_inode_getattr(struct mnt_idmap *idmap, const struct path *path, + struct kstat *stat, u32 request_mask, + unsigned int query_flags); --- a/fs/libfs.c +++ b/fs/libfs.c @@ -1647,7 +1647,13 @@ struct inode *alloc_anon_inode(struct su * that it already _is_ on the dirty list. */ inode->i_state = I_DIRTY; - inode->i_mode = S_IRUSR | S_IWUSR; + /* + * Historically anonymous inodes didn't have a type at all and + * userspace has come to rely on this. Internally they're just + * regular files but S_IFREG is masked off when reporting + * information to userspace. + */ + inode->i_mode = S_IFREG | S_IRUSR | S_IWUSR; inode->i_uid = current_fsuid(); inode->i_gid = current_fsgid(); inode->i_flags |= S_PRIVATE;