[PATCH] module: prevent warning when finit_module a 0 sized file

[PATCH] module: prevent warning when finit_module a 0 sized file

[Sasha Levin]

If we try to finit_module on a file sized 0 bytes vmalloc will
scream and spit out a warning.

Since modules have to be bigger than 0 bytes anyways we can just
check that beforehand and avoid the warning.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---
 kernel/module.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/module.c b/kernel/module.c
index 250092c..2e1ce2e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2527,6 +2527,12 @@ static int copy_module_from_fd(int fd, struct load_info *info)
 		err = -EFBIG;
 		goto out;
 	}
+
+	if (stat.size == 0) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	info->hdr = vmalloc(stat.size);
 	if (!info->hdr) {
 		err = -ENOMEM;
-- 
1.8.0.2

Re: [PATCH] module: prevent warning when finit_module a 0 sized file

[Rusty Russell]

Sasha Levin <sasha.levin@oracle.com> writes:

> If we try to finit_module on a file sized 0 bytes vmalloc will
> scream and spit out a warning.
>
> Since modules have to be bigger than 0 bytes anyways we can just
> check that beforehand and avoid the warning.

Applied, but I added the comment you somehow missed :)

Thanks,
Rusty.

diff --git a/kernel/module.c b/kernel/module.c
index 250092c..41bc118 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2527,6 +2527,13 @@ static int copy_module_from_fd(int fd, struct load_info *info)
 		err = -EFBIG;
 		goto out;
 	}
+
+	/* Don't hand 0 to vmalloc, it whines. */
+	if (stat.size == 0) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	info->hdr = vmalloc(stat.size);
 	if (!info->hdr) {
 		err = -ENOMEM;

Re: [PATCH] module: prevent warning when finit_module a 0 sized file

[Sasha Levin]

On 01/02/2013 07:41 PM, Rusty Russell wrote:
> Sasha Levin <sasha.levin@oracle.com> writes:
> 
>> If we try to finit_module on a file sized 0 bytes vmalloc will
>> scream and spit out a warning.
>>
>> Since modules have to be bigger than 0 bytes anyways we can just
>> check that beforehand and avoid the warning.
> 
> Applied, but I added the comment you somehow missed :)

Thanks!

I do have a somewhat related follow-up question:

When init_module() goes through the module loading process, it will try to vmalloc()
whatever size passed to it by the user, which may cause vmalloc() to scream and shout
if the size passed from userspace is too big.

Do you think that reading just the header and doing a quick elf_header_check() on
it before trying to read the entire file would make sense here?


Thanks,
Sasha

Re: [PATCH] module: prevent warning when finit_module a 0 sized file

[Rusty Russell]

Sasha Levin <sasha.levin@oracle.com> writes:
> On 01/02/2013 07:41 PM, Rusty Russell wrote:
>> Sasha Levin <sasha.levin@oracle.com> writes:
>> 
>>> If we try to finit_module on a file sized 0 bytes vmalloc will
>>> scream and spit out a warning.
>>>
>>> Since modules have to be bigger than 0 bytes anyways we can just
>>> check that beforehand and avoid the warning.
>> 
>> Applied, but I added the comment you somehow missed :)
>
> Thanks!
>
> I do have a somewhat related follow-up question:
>
> When init_module() goes through the module loading process, it will try to vmalloc()
> whatever size passed to it by the user, which may cause vmalloc() to scream and shout
> if the size passed from userspace is too big.
>
> Do you think that reading just the header and doing a quick elf_header_check() on
> it before trying to read the entire file would make sense here?

No.  Root asked, we do.  If modprobe wants to check the header, let it.

Cheers,
Rusty.