On Wed, 2024-08-28 at 15:51 -0400, Scott Mayhew wrote: > Marek Gresko reports that the root user on an NFS client is able to > change the security labels on files on an NFS filesystem that is > exported with root squashing enabled. > > The end of the kerneldoc comment for __vfs_setxattr_noperm() states: > > * This function requires the caller to lock the inode's i_mutex before it > * is executed. It also assumes that the caller will make the appropriate > * permission checks. > > nfsd_setattr() does do permissions checking via fh_verify() and > nfsd_permission(), but those don't do all the same permissions checks > that are done by security_inode_setxattr() and its related LSM hooks do. > > Since nfsd_setattr() is the only consumer of security_inode_setsecctx(), > simplest solution appears to be to replace the call to > __vfs_setxattr_noperm() with a call to __vfs_setxattr_locked(). This > fixes the above issue and has the added benefit of causing nfsd to > recall conflicting delegations on a file when a client tries to change > its security label. > > Reported-by: Marek Gresko <marek.gresko@xxxxxxxxxxxxxx> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=218809 > Signed-off-by: Scott Mayhew <smayhew@xxxxxxxxxx> > --- > security/selinux/hooks.c | 4 ++-- > security/smack/smack_lsm.c | 4 ++-- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c > index bfa61e005aac..400eca4ad0fb 100644 > --- a/security/selinux/hooks.c > +++ b/security/selinux/hooks.c > @@ -6660,8 +6660,8 @@ static int selinux_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen > */ > static int selinux_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen) > { > - return __vfs_setxattr_noperm(&nop_mnt_idmap, dentry, XATTR_NAME_SELINUX, > - ctx, ctxlen, 0); > + return __vfs_setxattr_locked(&nop_mnt_idmap, dentry, XATTR_NAME_SELINUX, > + ctx, ctxlen, 0, NULL); > } > > static int selinux_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen) > diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c > index 4164699cd4f6..002a1b9ed83a 100644 > --- a/security/smack/smack_lsm.c > +++ b/security/smack/smack_lsm.c > @@ -4880,8 +4880,8 @@ static int smack_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen) > > static int smack_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen) > { > - return __vfs_setxattr_noperm(&nop_mnt_idmap, dentry, XATTR_NAME_SMACK, > - ctx, ctxlen, 0); > + return __vfs_setxattr_locked(&nop_mnt_idmap, dentry, XATTR_NAME_SMACK, > + ctx, ctxlen, 0, NULL); > } > > static int smack_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen) Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
