* [PATCH] commoncap: check return value to avoid null pointer dereference
@ 2022-05-16 17:40 Yongzhi Liu
2022-05-16 18:14 ` Eric W. Biederman
2022-05-17 21:43 ` Al Viro
0 siblings, 2 replies; 3+ messages in thread
From: Yongzhi Liu @ 2022-05-16 17:40 UTC (permalink / raw)
To: serge, jmorris, viro, dhowells, ebiederm
Cc: linux-security-module, linux-kernel, Yongzhi Liu
The pointer inode is dereferenced before a null pointer
check on inode, hence if inode is actually null we will
get a null pointer dereference. Fix this by only dereferencing
inode after the null pointer check on inode.
Fixes: c6f493d631c ("VFS: security/: d_backing_inode() annotations")
Fixes: 8db6c34 ("Introduce v3 namespaced file capabilities")
Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
---
security/commoncap.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/security/commoncap.c b/security/commoncap.c
index 5fc8986..978f011 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -298,6 +298,8 @@ int cap_inode_need_killpriv(struct dentry *dentry)
struct inode *inode = d_backing_inode(dentry);
int error;
+ if (!inode)
+ return 0;
error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);
return error > 0;
}
@@ -545,11 +547,13 @@ int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
const struct vfs_cap_data *cap = *ivalue;
__u32 magic, nsmagic;
struct inode *inode = d_backing_inode(dentry);
- struct user_namespace *task_ns = current_user_ns(),
- *fs_ns = inode->i_sb->s_user_ns;
+ struct user_namespace *task_ns = current_user_ns(), *fs_ns;
kuid_t rootid;
size_t newsize;
+ if (!inode)
+ return -EINVAL;
+ fs_ns = inode->i_sb->s_user_ns;
if (!*ivalue)
return -EINVAL;
if (!validheader(size, cap))
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] commoncap: check return value to avoid null pointer dereference
2022-05-16 17:40 [PATCH] commoncap: check return value to avoid null pointer dereference Yongzhi Liu
@ 2022-05-16 18:14 ` Eric W. Biederman
2022-05-17 21:43 ` Al Viro
1 sibling, 0 replies; 3+ messages in thread
From: Eric W. Biederman @ 2022-05-16 18:14 UTC (permalink / raw)
To: Yongzhi Liu
Cc: serge, jmorris, viro, dhowells, linux-security-module, linux-kernel
Yongzhi Liu <lyz_cs@pku.edu.cn> writes:
> The pointer inode is dereferenced before a null pointer
> check on inode, hence if inode is actually null we will
> get a null pointer dereference. Fix this by only dereferencing
> inode after the null pointer check on inode.
>
> Fixes: c6f493d631c ("VFS: security/: d_backing_inode() annotations")
> Fixes: 8db6c34 ("Introduce v3 namespaced file capabilities")
I don't see how this fixes anything.
The dentry should be non-negative so d_backing_inode should always
return true.
> Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
> ---
> security/commoncap.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 5fc8986..978f011 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -298,6 +298,8 @@ int cap_inode_need_killpriv(struct dentry *dentry)
> struct inode *inode = d_backing_inode(dentry);
> int error;
>
> + if (!inode)
> + return 0;
How can dentry->d_inode be valid and d_backing_inode not be valid?
That would seem to be a bug elsewhere in the code if it actually happens.
> error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);
> return error > 0;
> }
> @@ -545,11 +547,13 @@ int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
> const struct vfs_cap_data *cap = *ivalue;
> __u32 magic, nsmagic;
> struct inode *inode = d_backing_inode(dentry);
> - struct user_namespace *task_ns = current_user_ns(),
> - *fs_ns = inode->i_sb->s_user_ns;
> + struct user_namespace *task_ns = current_user_ns(), *fs_ns;
> kuid_t rootid;
> size_t newsize;
>
> + if (!inode)
> + return -EINVAL;
> + fs_ns = inode->i_sb->s_user_ns;
> if (!*ivalue)
> return -EINVAL;
> if (!validheader(size, cap))
Same with this one. Short of a negative dentry I don't see how
d_backing_inode can be NULL, and we are talking about negative
dentries that should have been handled long before these two functions
are called.
Eric
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] commoncap: check return value to avoid null pointer dereference
2022-05-16 17:40 [PATCH] commoncap: check return value to avoid null pointer dereference Yongzhi Liu
2022-05-16 18:14 ` Eric W. Biederman
@ 2022-05-17 21:43 ` Al Viro
1 sibling, 0 replies; 3+ messages in thread
From: Al Viro @ 2022-05-17 21:43 UTC (permalink / raw)
To: Yongzhi Liu
Cc: serge, jmorris, dhowells, ebiederm, linux-security-module, linux-kernel
On Mon, May 16, 2022 at 10:40:02AM -0700, Yongzhi Liu wrote:
> The pointer inode is dereferenced before a null pointer
> check on inode, hence if inode is actually null we will
> get a null pointer dereference. Fix this by only dereferencing
> inode after the null pointer check on inode.
>
> Fixes: c6f493d631c ("VFS: security/: d_backing_inode() annotations")
> Fixes: 8db6c34 ("Introduce v3 namespaced file capabilities")
>
> Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
> ---
> security/commoncap.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 5fc8986..978f011 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -298,6 +298,8 @@ int cap_inode_need_killpriv(struct dentry *dentry)
> struct inode *inode = d_backing_inode(dentry);
> int error;
>
> + if (!inode)
> + return 0;
> error = __vfs_getxattr(dentry, inode, XATTR_NAME_CAPS, NULL, 0);
> return error > 0;
> }
Huh? AFAICS, that has all of two callers - notify_change() and
dentry_needs_remove_privs(). Both of them should never be called on
negative dentries and both would have blown up well before the call of
security_inode_need_killpriv().
> @@ -545,11 +547,13 @@ int cap_convert_nscap(struct user_namespace *mnt_userns, struct dentry *dentry,
> const struct vfs_cap_data *cap = *ivalue;
> __u32 magic, nsmagic;
> struct inode *inode = d_backing_inode(dentry);
> - struct user_namespace *task_ns = current_user_ns(),
> - *fs_ns = inode->i_sb->s_user_ns;
> + struct user_namespace *task_ns = current_user_ns(), *fs_ns;
> kuid_t rootid;
> size_t newsize;
>
> + if (!inode)
> + return -EINVAL;
> + fs_ns = inode->i_sb->s_user_ns;
> if (!*ivalue)
> return -EINVAL;
> if (!validheader(size, cap))
... and that one come from vfs_setxattr(). Again, calling that on a negative
dentry is an oopsable bug. If you have any reproducers, please post the stack
traces so it would be possible to deal with the underlying problem.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-05-17 21:44 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2022-05-16 17:40 [PATCH] commoncap: check return value to avoid null pointer dereference Yongzhi Liu
2022-05-16 18:14 ` Eric W. Biederman
2022-05-17 21:43 ` Al Viro
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