| Message ID | 20250407-work-anon_inode-v1-1-53a44c20d44e@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | fs: harden anon inodes | expand |
On Mon, 2025-04-07 at 11:54 +0200, Christian Brauner wrote: > 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. > > Fixes: af153bb63a336 ("vfs: catch invalid modes in may_open()") > 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> > --- > fs/anon_inodes.c | 36 ++++++++++++++++++++++++++++++++++++ > fs/internal.h | 3 +++ > fs/libfs.c | 2 +- > 3 files changed, 40 insertions(+), 1 deletion(-) > > diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c > index 583ac81669c2..42e4b9c34f89 100644 > --- a/fs/anon_inodes.c > +++ b/fs/anon_inodes.c > @@ -24,9 +24,43 @@ > > #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. Weird. Does anything actually depend on this? ISTM that they should report a file type. > + * > + * 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(). > */ > @@ -66,6 +100,7 @@ static struct inode *anon_inode_make_secure_inode( > 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; > } > diff --git a/fs/internal.h b/fs/internal.h > index b9b3e29a73fd..717dc9eb6185 100644 > --- a/fs/internal.h > +++ b/fs/internal.h > @@ -343,3 +343,6 @@ static inline bool path_mounted(const struct path *path) > 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); > diff --git a/fs/libfs.c b/fs/libfs.c > index 6393d7c49ee6..0ad3336f5b49 100644 > --- a/fs/libfs.c > +++ b/fs/libfs.c > @@ -1647,7 +1647,7 @@ struct inode *alloc_anon_inode(struct super_block *s) > * that it already _is_ on the dirty list. > */ > inode->i_state = I_DIRTY; > - inode->i_mode = S_IRUSR | S_IWUSR; > + inode->i_mode = S_IFREG | S_IRUSR | S_IWUSR; > inode->i_uid = current_fsuid(); > inode->i_gid = current_fsgid(); > inode->i_flags |= S_PRIVATE; >
On Mon, Apr 07, 2025 at 08:19:25AM -0400, Jeff Layton wrote: > On Mon, 2025-04-07 at 11:54 +0200, Christian Brauner wrote: > > 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. > > > > Fixes: af153bb63a336 ("vfs: catch invalid modes in may_open()") > > 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> > > --- > > fs/anon_inodes.c | 36 ++++++++++++++++++++++++++++++++++++ > > fs/internal.h | 3 +++ > > fs/libfs.c | 2 +- > > 3 files changed, 40 insertions(+), 1 deletion(-) > > > > diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c > > index 583ac81669c2..42e4b9c34f89 100644 > > --- a/fs/anon_inodes.c > > +++ b/fs/anon_inodes.c > > @@ -24,9 +24,43 @@ > > > > #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. > > Weird. Does anything actually depend on this? Yeah, lsof failed and started complaining about this. They're checking the mode to recognize anonymous inodes. And tbf, it works to generically recognizer proper anonymous inodes because they came come from very different superblocks (dmabuf, drm, vfio, anon_inode_mnt etc.). > > ISTM that they should report a file type. I agree but that ship has probably sailed.
On Mon 07-04-25 11:54:15, Christian Brauner wrote: > 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. > > Fixes: af153bb63a336 ("vfs: catch invalid modes in may_open()") > 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> Looks good. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > fs/anon_inodes.c | 36 ++++++++++++++++++++++++++++++++++++ > fs/internal.h | 3 +++ > fs/libfs.c | 2 +- > 3 files changed, 40 insertions(+), 1 deletion(-) > > diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c > index 583ac81669c2..42e4b9c34f89 100644 > --- a/fs/anon_inodes.c > +++ b/fs/anon_inodes.c > @@ -24,9 +24,43 @@ > > #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(). > */ > @@ -66,6 +100,7 @@ static struct inode *anon_inode_make_secure_inode( > 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; > } > diff --git a/fs/internal.h b/fs/internal.h > index b9b3e29a73fd..717dc9eb6185 100644 > --- a/fs/internal.h > +++ b/fs/internal.h > @@ -343,3 +343,6 @@ static inline bool path_mounted(const struct path *path) > 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); > diff --git a/fs/libfs.c b/fs/libfs.c > index 6393d7c49ee6..0ad3336f5b49 100644 > --- a/fs/libfs.c > +++ b/fs/libfs.c > @@ -1647,7 +1647,7 @@ struct inode *alloc_anon_inode(struct super_block *s) > * that it already _is_ on the dirty list. > */ > inode->i_state = I_DIRTY; > - inode->i_mode = S_IRUSR | S_IWUSR; > + inode->i_mode = S_IFREG | S_IRUSR | S_IWUSR; > inode->i_uid = current_fsuid(); > inode->i_gid = current_fsgid(); > inode->i_flags |= S_PRIVATE; > > -- > 2.47.2 >
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c index 583ac81669c2..42e4b9c34f89 100644 --- a/fs/anon_inodes.c +++ b/fs/anon_inodes.c @@ -24,9 +24,43 @@ #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(). */ @@ -66,6 +100,7 @@ static struct inode *anon_inode_make_secure_inode( 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; } diff --git a/fs/internal.h b/fs/internal.h index b9b3e29a73fd..717dc9eb6185 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -343,3 +343,6 @@ static inline bool path_mounted(const struct path *path) 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); diff --git a/fs/libfs.c b/fs/libfs.c index 6393d7c49ee6..0ad3336f5b49 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -1647,7 +1647,7 @@ struct inode *alloc_anon_inode(struct super_block *s) * that it already _is_ on the dirty list. */ inode->i_state = I_DIRTY; - inode->i_mode = S_IRUSR | S_IWUSR; + inode->i_mode = S_IFREG | S_IRUSR | S_IWUSR; inode->i_uid = current_fsuid(); inode->i_gid = current_fsgid(); inode->i_flags |= S_PRIVATE;
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. Fixes: af153bb63a336 ("vfs: catch invalid modes in may_open()") 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> --- fs/anon_inodes.c | 36 ++++++++++++++++++++++++++++++++++++ fs/internal.h | 3 +++ fs/libfs.c | 2 +- 3 files changed, 40 insertions(+), 1 deletion(-)