On 13-Jan 10:42, 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. > > It should be kept in mind that this function gives access to cached > entries which can be removed, for instance on security_inode_free(). > > This is based on Peter Moody's patch: > https://sourceforge.net/p/linux-ima/mailman/message/33036180/ > > [1] https://lkml.org/lkml/2019/9/10/393 > > Signed-off-by: Florent Revest <revest@xxxxxxxxxx> Reviewed-by: KP Singh <kpsingh@xxxxxxxxxxxx> > --- > include/linux/ima.h | 6 ++++ > security/integrity/ima/ima_main.c | 49 +++++++++++++++++++++++++++++++ > 2 files changed, 55 insertions(+) > > diff --git a/include/linux/ima.h b/include/linux/ima.h > index f4644c54f648..1659217e9b60 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 2272c3255c7d..9fe949c6a530 100644 > --- a/security/integrity/ima/ima_main.c > +++ b/security/integrity/ima/ima_main.c > @@ -445,6 +445,55 @@ 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 and > + * is in the iint cache. > + * @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. > + * 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. > + * The file hash returned is based on the entire file, including the appended > + * signature. > + * > + * 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 > -- > 2.25.0.rc1.283.g88dfdc4193-goog >
