2020-09-16 18:40:56

by KP Singh

Subject: [PATCH] ima: Fix NULL pointer dereference in ima_file_hash

From: KP Singh <[email protected]>

ima_file_hash can be called when there is no iint->ima_hash available
even though the inode exists in the integrity cache.

An example where this can happen (suggested by Jann Horn):

Process A does:

while(1) {
unlink("/tmp/imafoo");
fd = open("/tmp/imafoo", O_RDWR|O_CREAT|O_TRUNC, 0700);
if (fd == -1) {
perror("open");
continue;
}
write(fd, "A", 1);
close(fd);
}

and Process B does:

while (1) {
int fd = open("/tmp/imafoo", O_RDONLY);
if (fd == -1)
continue;
char *mapping = mmap(NULL, 0x1000, PROT_READ|PROT_EXEC,
MAP_PRIVATE, fd, 0);
if (mapping != MAP_FAILED)
munmap(mapping, 0x1000);
close(fd);
}

Due to the race to get the iint->mutex between ima_file_hash and
process_measurement iint->ima_hash could still be NULL.

Fixes: 6beea7afcc72 ("ima: add the ability to query the cached hash of a given file")
Signed-off-by: KP Singh <[email protected]>
---
security/integrity/ima/ima_main.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 8a91711ca79b..4c86cd4eece0 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -531,6 +531,16 @@ int ima_file_hash(struct file *file, char *buf, size_t buf_size)
return -EOPNOTSUPP;

mutex_lock(&iint->mutex);
+
+ /*
+ * ima_file_hash can be called when ima_collect_measurement has still
+ * not been called, we might not always have a hash.
+ */
+ if (!iint->ima_hash) {
+ mutex_unlock(&iint->mutex);
+ return -EOPNOTSUPP;
+ }
+
if (buf) {
size_t copied_size;

--
2.28.0.618.gf4bc123cb7-goog

2020-09-16 20:27:49

by Florent Revest

Subject: Re: [PATCH] ima: Fix NULL pointer dereference in ima_file_hash

Reviewed-by: Florent Revest <[email protected]>

On Wed, 2020-09-16 at 12:05 +0000, KP Singh wrote:
> From: KP Singh <[email protected]>
>
> ima_file_hash can be called when there is no iint->ima_hash available
> even though the inode exists in the integrity cache.
>
> An example where this can happen (suggested by Jann Horn):
>
> Process A does:
>
> while(1) {
> unlink("/tmp/imafoo");
> fd = open("/tmp/imafoo", O_RDWR|O_CREAT|O_TRUNC, 0700);
> if (fd == -1) {
> perror("open");
> continue;
> }
> write(fd, "A", 1);
> close(fd);
> }
>
> and Process B does:
>
> while (1) {
> int fd = open("/tmp/imafoo", O_RDONLY);
> if (fd == -1)
> continue;
> char *mapping = mmap(NULL, 0x1000, PROT_READ|PROT_EXEC,
> MAP_PRIVATE, fd, 0);
> if (mapping != MAP_FAILED)
> munmap(mapping, 0x1000);
> close(fd);
> }
>
> Due to the race to get the iint->mutex between ima_file_hash and
> process_measurement iint->ima_hash could still be NULL.
>
> Fixes: 6beea7afcc72 ("ima: add the ability to query the cached hash
> of a given file")
> Signed-off-by: KP Singh <[email protected]>
> ---
> security/integrity/ima/ima_main.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/security/integrity/ima/ima_main.c
> b/security/integrity/ima/ima_main.c
> index 8a91711ca79b..4c86cd4eece0 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -531,6 +531,16 @@ int ima_file_hash(struct file *file, char *buf,
> size_t buf_size)
> return -EOPNOTSUPP;
>
> mutex_lock(&iint->mutex);
> +
> + /*
> + * ima_file_hash can be called when ima_collect_measurement has
> still
> + * not been called, we might not always have a hash.
> + */
> + if (!iint->ima_hash) {
> + mutex_unlock(&iint->mutex);
> + return -EOPNOTSUPP;
> + }
> +
> if (buf) {
> size_t copied_size;
>

2020-09-16 20:47:21

by KP Singh

Subject: Re: [PATCH] ima: Fix NULL pointer dereference in ima_file_hash

Somehow this patch does not seem to have been picked up by any of the
mailing list archives and I am not sure if this was delivered to the
lists. I will send a v2 and add Florent's Reviewed-by tag.

On Wed, Sep 16, 2020 at 2:41 PM Florent Revest <[email protected]> wrote:
>
> Reviewed-by: Florent Revest <[email protected]>
>
> On Wed, 2020-09-16 at 12:05 +0000, KP Singh wrote:
> > From: KP Singh <[email protected]>
> >
> > ima_file_hash can be called when there is no iint->ima_hash available
> > even though the inode exists in the integrity cache.
> >
> > An example where this can happen (suggested by Jann Horn):
> >
> > Process A does:
> >
> > while(1) {
> > unlink("/tmp/imafoo");
> > fd = open("/tmp/imafoo", O_RDWR|O_CREAT|O_TRUNC, 0700);
> > if (fd == -1) {
> > perror("open");
> > continue;
> > }
> > write(fd, "A", 1);
> > close(fd);
> > }
> >
> > and Process B does:
> >
> > while (1) {
> > int fd = open("/tmp/imafoo", O_RDONLY);
> > if (fd == -1)
> > continue;
> > char *mapping = mmap(NULL, 0x1000, PROT_READ|PROT_EXEC,
> > MAP_PRIVATE, fd, 0);
> > if (mapping != MAP_FAILED)
> > munmap(mapping, 0x1000);
> > close(fd);
> > }
> >
> > Due to the race to get the iint->mutex between ima_file_hash and
> > process_measurement iint->ima_hash could still be NULL.
> >
> > Fixes: 6beea7afcc72 ("ima: add the ability to query the cached hash
> > of a given file")
> > Signed-off-by: KP Singh <[email protected]>
> > ---
> > security/integrity/ima/ima_main.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/security/integrity/ima/ima_main.c
> > b/security/integrity/ima/ima_main.c
> > index 8a91711ca79b..4c86cd4eece0 100644
> > --- a/security/integrity/ima/ima_main.c
> > +++ b/security/integrity/ima/ima_main.c
> > @@ -531,6 +531,16 @@ int ima_file_hash(struct file *file, char *buf,
> > size_t buf_size)
> > return -EOPNOTSUPP;
> >
> > mutex_lock(&iint->mutex);
> > +
> > + /*
> > + * ima_file_hash can be called when ima_collect_measurement has
> > still
> > + * not been called, we might not always have a hash.
> > + */
> > + if (!iint->ima_hash) {
> > + mutex_unlock(&iint->mutex);
> > + return -EOPNOTSUPP;
> > + }
> > +
> > if (buf) {
> > size_t copied_size;
> >
>