| Message ID | 20221102061659.920334-1-chenxiaosong2@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | cifs: fix use-after-free on the link name | expand |
xfstests generic/011 can reproduce this bug in about 10+ minutes, enable
CONFIG_KASAN=y, my mount option is: -o mfsymlinks,vers=3.0 -o
context=system_u:object_r:unlabeled_t:s0
在 2022/11/3 8:59, Steve French 写道:
> Looks promising. How common was the xfstest failure in your setup?
ChenXiaoSong <chenxiaosong2@huawei.com> writes: > xfstests generic/011 reported use-after-free bug as follows: > > BUG: KASAN: use-after-free in __d_alloc+0x269/0x859 > Read of size 15 at addr ffff8880078933a0 by task dirstress/952 > > CPU: 1 PID: 952 Comm: dirstress Not tainted 6.1.0-rc3+ #77 > Call Trace: > __dump_stack+0x23/0x29 > dump_stack_lvl+0x51/0x73 > print_address_description+0x67/0x27f > print_report+0x3e/0x5c > kasan_report+0x7b/0xa8 > kasan_check_range+0x1b2/0x1c1 > memcpy+0x22/0x5d > __d_alloc+0x269/0x859 > d_alloc+0x45/0x20c > d_alloc_parallel+0xb2/0x8b2 > lookup_open+0x3b8/0x9f9 > open_last_lookups+0x63d/0xc26 > path_openat+0x11a/0x261 > do_filp_open+0xcc/0x168 > do_sys_openat2+0x13b/0x3f7 > do_sys_open+0x10f/0x146 > __se_sys_creat+0x27/0x2e > __x64_sys_creat+0x55/0x6a > do_syscall_64+0x40/0x96 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > Allocated by task 952: > kasan_save_stack+0x1f/0x42 > kasan_set_track+0x21/0x2a > kasan_save_alloc_info+0x17/0x1d > __kasan_kmalloc+0x7e/0x87 > __kmalloc_node_track_caller+0x59/0x155 > kstrndup+0x60/0xe6 > parse_mf_symlink+0x215/0x30b > check_mf_symlink+0x260/0x36a > cifs_get_inode_info+0x14e1/0x1690 > cifs_revalidate_dentry_attr+0x70d/0x964 > cifs_revalidate_dentry+0x36/0x62 > cifs_d_revalidate+0x162/0x446 > lookup_open+0x36f/0x9f9 > open_last_lookups+0x63d/0xc26 > path_openat+0x11a/0x261 > do_filp_open+0xcc/0x168 > do_sys_openat2+0x13b/0x3f7 > do_sys_open+0x10f/0x146 > __se_sys_creat+0x27/0x2e > __x64_sys_creat+0x55/0x6a > do_syscall_64+0x40/0x96 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > Freed by task 950: > kasan_save_stack+0x1f/0x42 > kasan_set_track+0x21/0x2a > kasan_save_free_info+0x1c/0x34 > ____kasan_slab_free+0x1c1/0x1d5 > __kasan_slab_free+0xe/0x13 > __kmem_cache_free+0x29a/0x387 > kfree+0xd3/0x10e > cifs_fattr_to_inode+0xb6a/0xc8c > cifs_get_inode_info+0x3cb/0x1690 > cifs_revalidate_dentry_attr+0x70d/0x964 > cifs_revalidate_dentry+0x36/0x62 > cifs_d_revalidate+0x162/0x446 > lookup_open+0x36f/0x9f9 > open_last_lookups+0x63d/0xc26 > path_openat+0x11a/0x261 > do_filp_open+0xcc/0x168 > do_sys_openat2+0x13b/0x3f7 > do_sys_open+0x10f/0x146 > __se_sys_creat+0x27/0x2e > __x64_sys_creat+0x55/0x6a > do_syscall_64+0x40/0x96 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > When opened a symlink, link name is from 'inode->i_link', but it may be > reset to a new value when revalidate the dentry. If some processes get the > link name on the race scenario, then UAF will happen on link name. > > Fix this by implementing 'get_link' interface to duplicate the link name. > > Fixes: 76894f3e2f71 ("cifs: improve symlink handling for smb2+") > Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com> > --- > fs/cifs/cifsfs.c | 21 ++++++++++++++++++++- > fs/cifs/inode.c | 5 ----- > 2 files changed, 20 insertions(+), 6 deletions(-) Good catch. I was also able to reproduce it with CONFIG_KASAN=y when running xfstests generic/011 multiple times. > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c > index d0b9fec111aa..bb9592594fcc 100644 > --- a/fs/cifs/cifsfs.c > +++ b/fs/cifs/cifsfs.c > @@ -1143,8 +1143,27 @@ const struct inode_operations cifs_file_inode_ops = { > .fiemap = cifs_fiemap, > }; > > +const char *cifs_get_link(struct dentry *dentry, struct inode *inode, > + struct delayed_call *done) > +{ Aren't you supposed to return ERR_PTR(-ECHILD) when !dentry (e.g. rcu-walk mode)? > + char *target_path = NULL; > + > + spin_lock(&inode->i_lock); > + if (likely(CIFS_I(inode)->symlink_target)) > + target_path = kstrdup(CIFS_I(inode)->symlink_target, > + GFP_ATOMIC); > + spin_unlock(&inode->i_lock); Can't you get rid of above kmalloc() inside spin lock and do something like target_path = kmalloc(PATH_MAX, GFP_KERNEL); if (!target_path) return ERR_PTR(-ENOMEM); spin_lock(&inode->i_lock); if (likely(CIFS_I(inode)->symlink_target)) strscpy(target_path, CIFS_I(inode)->symlink_target, PATH_MAX); else { kfree(target_path); target_path = ERR_PTR(-EOPNOTSUPP); } spin_unlock(&inode->i_lock); if (!IS_ERR(target_path)) set_delayed_call(done, kfree_link, target_path); return target_path;
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c index d0b9fec111aa..bb9592594fcc 100644 --- a/fs/cifs/cifsfs.c +++ b/fs/cifs/cifsfs.c @@ -1143,8 +1143,27 @@ const struct inode_operations cifs_file_inode_ops = { .fiemap = cifs_fiemap, }; +const char *cifs_get_link(struct dentry *dentry, struct inode *inode, + struct delayed_call *done) +{ + char *target_path = NULL; + + spin_lock(&inode->i_lock); + if (likely(CIFS_I(inode)->symlink_target)) + target_path = kstrdup(CIFS_I(inode)->symlink_target, + GFP_ATOMIC); + spin_unlock(&inode->i_lock); + + if (target_path) + set_delayed_call(done, kfree_link, target_path); + else + target_path = ERR_PTR(-EOPNOTSUPP); + + return target_path; +} + const struct inode_operations cifs_symlink_inode_ops = { - .get_link = simple_get_link, + .get_link = cifs_get_link, .permission = cifs_permission, .listxattr = cifs_listxattr, }; diff --git a/fs/cifs/inode.c b/fs/cifs/inode.c index 9bde08d44617..4e2ca3c6e5c0 100644 --- a/fs/cifs/inode.c +++ b/fs/cifs/inode.c @@ -215,11 +215,6 @@ cifs_fattr_to_inode(struct inode *inode, struct cifs_fattr *fattr) kfree(cifs_i->symlink_target); cifs_i->symlink_target = fattr->cf_symlink_target; fattr->cf_symlink_target = NULL; - - if (unlikely(!cifs_i->symlink_target)) - inode->i_link = ERR_PTR(-EOPNOTSUPP); - else - inode->i_link = cifs_i->symlink_target; } spin_unlock(&inode->i_lock);
xfstests generic/011 reported use-after-free bug as follows: BUG: KASAN: use-after-free in __d_alloc+0x269/0x859 Read of size 15 at addr ffff8880078933a0 by task dirstress/952 CPU: 1 PID: 952 Comm: dirstress Not tainted 6.1.0-rc3+ #77 Call Trace: __dump_stack+0x23/0x29 dump_stack_lvl+0x51/0x73 print_address_description+0x67/0x27f print_report+0x3e/0x5c kasan_report+0x7b/0xa8 kasan_check_range+0x1b2/0x1c1 memcpy+0x22/0x5d __d_alloc+0x269/0x859 d_alloc+0x45/0x20c d_alloc_parallel+0xb2/0x8b2 lookup_open+0x3b8/0x9f9 open_last_lookups+0x63d/0xc26 path_openat+0x11a/0x261 do_filp_open+0xcc/0x168 do_sys_openat2+0x13b/0x3f7 do_sys_open+0x10f/0x146 __se_sys_creat+0x27/0x2e __x64_sys_creat+0x55/0x6a do_syscall_64+0x40/0x96 entry_SYSCALL_64_after_hwframe+0x63/0xcd Allocated by task 952: kasan_save_stack+0x1f/0x42 kasan_set_track+0x21/0x2a kasan_save_alloc_info+0x17/0x1d __kasan_kmalloc+0x7e/0x87 __kmalloc_node_track_caller+0x59/0x155 kstrndup+0x60/0xe6 parse_mf_symlink+0x215/0x30b check_mf_symlink+0x260/0x36a cifs_get_inode_info+0x14e1/0x1690 cifs_revalidate_dentry_attr+0x70d/0x964 cifs_revalidate_dentry+0x36/0x62 cifs_d_revalidate+0x162/0x446 lookup_open+0x36f/0x9f9 open_last_lookups+0x63d/0xc26 path_openat+0x11a/0x261 do_filp_open+0xcc/0x168 do_sys_openat2+0x13b/0x3f7 do_sys_open+0x10f/0x146 __se_sys_creat+0x27/0x2e __x64_sys_creat+0x55/0x6a do_syscall_64+0x40/0x96 entry_SYSCALL_64_after_hwframe+0x63/0xcd Freed by task 950: kasan_save_stack+0x1f/0x42 kasan_set_track+0x21/0x2a kasan_save_free_info+0x1c/0x34 ____kasan_slab_free+0x1c1/0x1d5 __kasan_slab_free+0xe/0x13 __kmem_cache_free+0x29a/0x387 kfree+0xd3/0x10e cifs_fattr_to_inode+0xb6a/0xc8c cifs_get_inode_info+0x3cb/0x1690 cifs_revalidate_dentry_attr+0x70d/0x964 cifs_revalidate_dentry+0x36/0x62 cifs_d_revalidate+0x162/0x446 lookup_open+0x36f/0x9f9 open_last_lookups+0x63d/0xc26 path_openat+0x11a/0x261 do_filp_open+0xcc/0x168 do_sys_openat2+0x13b/0x3f7 do_sys_open+0x10f/0x146 __se_sys_creat+0x27/0x2e __x64_sys_creat+0x55/0x6a do_syscall_64+0x40/0x96 entry_SYSCALL_64_after_hwframe+0x63/0xcd When opened a symlink, link name is from 'inode->i_link', but it may be reset to a new value when revalidate the dentry. If some processes get the link name on the race scenario, then UAF will happen on link name. Fix this by implementing 'get_link' interface to duplicate the link name. Fixes: 76894f3e2f71 ("cifs: improve symlink handling for smb2+") Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com> --- fs/cifs/cifsfs.c | 21 ++++++++++++++++++++- fs/cifs/inode.c | 5 ----- 2 files changed, 20 insertions(+), 6 deletions(-)