On Wed, 2020-01-08 at 11:05 -0500, Mimi Zohar wrote: > On Mon, 2020-01-06 at 17:25 +0100, Florent Revest wrote: > > From: Florent Revest <revest@xxxxxxxxxx> > > > > This allows other parts of the kernel (perhaps a stacked LSM > > allowing > > system monitoring, eg. the proposed KRSI LSM [1]) to retrieve the > > hash > > of a given file from IMA if it's present in the iint cache. > > > > It's true that the existence of the hash means that it's also in > > the > > audit logs or in > > /sys/kernel/security/ima/ascii_runtime_measurements, > > but it can be difficult to pull that information out for every > > subsequent exec. This is especially true if a given host has been > > up > > for a long time and the file was first measured a long time ago. > > > > This is based on Peter Moody's patch: > > https://sourceforge.net/p/linux-ima/mailman/message/33036180/ > > FYI, but unlike the audit log/IMA measurement list, the iint cache > entries can be removed. Refer to security_inode_free(). Perhaps > mention of this difference should be included, here, in the patch > description. Sure, I added a comment about this in a v3. > > [1] https://lkml.org/lkml/2019/9/10/393 > > > > Signed-off-by: Florent Revest <revest@xxxxxxxxxx> > > Assuming, with the above difference, you're still interested in > having this feature upstreamed and addressing the comments above and > below: > > Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx> Thank you. Yes we are still interested in this feature! > > --- > > include/linux/ima.h | 6 ++++ > > security/integrity/ima/ima_main.c | 46 > > +++++++++++++++++++++++++++++++ > > 2 files changed, 52 insertions(+) > > > > diff --git a/include/linux/ima.h b/include/linux/ima.h > > index 6d904754d858..d621c65ba9a5 100644 > > --- a/include/linux/ima.h > > +++ b/include/linux/ima.h > > @@ -23,6 +23,7 @@ extern int ima_read_file(struct file *file, enum > > kernel_read_file_id id); > > extern int ima_post_read_file(struct file *file, void *buf, loff_t > > size, > > enum kernel_read_file_id id); > > extern void ima_post_path_mknod(struct dentry *dentry); > > +extern int ima_file_hash(struct file *file, char *buf, size_t > > buf_size); > > extern void ima_kexec_cmdline(const void *buf, int size); > > > > #ifdef CONFIG_IMA_KEXEC > > @@ -91,6 +92,11 @@ static inline void ima_post_path_mknod(struct > > dentry *dentry) > > return; > > } > > > > +static inline int ima_file_hash(struct file *file, char *buf, > > size_t buf_size) > > +{ > > + return -EOPNOTSUPP; > > +} > > + > > static inline void ima_kexec_cmdline(const void *buf, int size) {} > > #endif /* CONFIG_IMA */ > > > > diff --git a/security/integrity/ima/ima_main.c > > b/security/integrity/ima/ima_main.c > > index d7e987baf127..3799b6c6c3b8 100644 > > --- a/security/integrity/ima/ima_main.c > > +++ b/security/integrity/ima/ima_main.c > > @@ -445,6 +445,52 @@ int ima_file_check(struct file *file, int > > mask) > > } > > EXPORT_SYMBOL_GPL(ima_file_check); > > > > +/** > > + * ima_file_hash - return the stored measurement if a file has > > been hashed. > > + * @file: pointer to the file > > + * @buf: buffer in which to store the hash > > + * @buf_size: length of the buffer > > + * > > + * On success, return the hash algorithm (as defined in the enum > > hash_algo). > > + * If buf is not NULL, this function also outputs the hash into > > buf. > > As of Linux 5.4.y, IMA support for appended file signatures was > added. Should we indicate that the file hash returned is based on the > entire file, including the appended signature? > > Mimi Of course it never hurts to add a comment. :) I'll send a v3 with this added. > > > + * If the hash is larger than buf_size, then only buf_size bytes > > will be copied. > > + * It generally just makes sense to pass a buffer capable of > > holding the largest > > + * possible hash: IMA_MAX_DIGEST_SIZE > > + * > > + * If IMA is disabled or if no measurement is available, return > > -EOPNOTSUPP. > > + * If the parameters are incorrect, return -EINVAL. > > + */ > > +int ima_file_hash(struct file *file, char *buf, size_t buf_size) > > +{ > > + struct inode *inode; > > + struct integrity_iint_cache *iint; > > + int hash_algo; > > + > > + if (!file) > > + return -EINVAL; > > + > > + if (!ima_policy_flag) > > + return -EOPNOTSUPP; > > + > > + inode = file_inode(file); > > + iint = integrity_iint_find(inode); > > + if (!iint) > > + return -EOPNOTSUPP; > > + > > + mutex_lock(&iint->mutex); > > + if (buf) { > > + size_t copied_size; > > + > > + copied_size = min_t(size_t, iint->ima_hash->length, > > buf_size); > > + memcpy(buf, iint->ima_hash->digest, copied_size); > > + } > > + hash_algo = iint->ima_hash->algo; > > + mutex_unlock(&iint->mutex); > > + > > + return hash_algo; > > +} > > +EXPORT_SYMBOL_GPL(ima_file_hash); > > + > > /** > > * ima_post_create_tmpfile - mark newly created tmpfile as new > > * @file : newly created tmpfile
