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authorAl Viro <viro@zeniv.linux.org.uk>2019-05-12 17:09:01 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2019-05-25 17:59:58 -0400
commit2527b284defaeadf74829b0b0bd3207ca7f165eb (patch)
tree5995146d7d565f6e01c8dbd84b49eab9f963d4fc /fs
parentbb7b6b2bbdb827e68cd506c8f5e3ba13215cccb2 (diff)
move the capability checks from sget_userns() to legacy_get_tree()
1) all call chains leading to sget_userns() pass through ->mount() instances. 2) none of ->mount() instances is ever called directly - the only call site is legacy_get_tree() 3) all remaining ->mount() instances end up calling sget_userns() IOW, we might as well do the capability checks just before calling ->mount(). As for the arguments passed to mount_capable(), in case of call chains to sget_userns() going through sget(), we either don't call mount_capable() at all, or pass current_user_ns() to it. The call chains going through mount_pseudo_xattr() don't call mount_capable() at all (SB_KERNMOUNT in flags on those). That could've been split into smaller steps (lifting the checks into sget(), then callers of sget(), then all the way to the entries of every ->mount() out there, then to the sole caller), but that would be too much churn for little benefit... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/fs_context.c5
-rw-r--r--fs/internal.h2
-rw-r--r--fs/super.c4
3 files changed, 7 insertions, 4 deletions
diff --git a/fs/fs_context.c b/fs/fs_context.c
index a47ccd5a4a78..746a5871959c 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -662,6 +662,11 @@ static int legacy_get_tree(struct fs_context *fc)
struct super_block *sb;
struct dentry *root;
+ if (!(fc->sb_flags & (SB_KERNMOUNT|SB_SUBMOUNT))) {
+ if (!mount_capable(fc->fs_type, current_user_ns()))
+ return -EPERM;
+ }
+
root = fc->fs_type->mount(fc->fs_type, fc->sb_flags,
fc->source, ctx->legacy_data);
if (IS_ERR(root))
diff --git a/fs/internal.h b/fs/internal.h
index 1ac2b8f6c621..65db901420af 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -18,6 +18,7 @@ struct path;
struct mount;
struct shrink_control;
struct fs_context;
+struct user_namespace;
/*
* block_dev.c
@@ -113,6 +114,7 @@ extern struct file *alloc_empty_file_noaccount(int, const struct cred *);
extern int reconfigure_super(struct fs_context *);
extern bool trylock_super(struct super_block *sb);
extern struct super_block *user_get_super(dev_t);
+extern bool mount_capable(struct file_system_type *, struct user_namespace *);
/*
* open.c
diff --git a/fs/super.c b/fs/super.c
index 6919f5c728f0..bdb03255c7ea 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -583,10 +583,6 @@ struct super_block *sget_userns(struct file_system_type *type,
struct super_block *old;
int err;
- if (!(flags & (SB_KERNMOUNT|SB_SUBMOUNT))) {
- if (!mount_capable(type, user_ns))
- return ERR_PTR(-EPERM);
- }
retry:
spin_lock(&sb_lock);
if (test) {