LinuxLists.cc - [PATCH] module: fix [e_shstrndx].sh

2022-05-03 22:18:02

Subject: [PATCH] module: fix [e_shstrndx].sh_size=0 OOB access

2022-05-04 08:08:46

Subject: Re: [PATCH] module: fix [e_shstrndx].sh_size=0 OOB access

On Tue, May 03, 2022 at 05:57:59PM +0300, Alexey Dobriyan wrote:
> It is trivial to craft a module to trigger OOB access in this line:
>
> if (info->secstrings[strhdr->sh_size - 1] != '\0') {
>
> BUG: unable to handle page fault for address: ffffc90000aa0fff
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 100000067 P4D 100000067 PUD 100066067 PMD 10436f067 PTE 0
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 7 PID: 1215 Comm: insmod Not tainted 5.18.0-rc5-00007-g9bf578647087-dirty #10
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
> RIP: 0010:load_module+0x19b/0x2391
>
> Signed-off-by: Alexey Dobriyan <[email protected]>

Thanks! Can you resend and Cc stable? This seems like an issue present for
a long time, can you identify the commit which introduced the issue?

Luis

2022-05-04 12:47:32

by Alexey Dobriyan

[permalink] [raw]

Subject: [PATCH v2] module: fix [e_shstrndx].sh_size=0 OOB access

It is trivial to craft a module to trigger OOB access in this line:

if (info->secstrings[strhdr->sh_size - 1] != '\0') {

BUG: unable to handle page fault for address: ffffc90000aa0fff
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 100000067 P4D 100000067 PUD 100066067 PMD 10436f067 PTE 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 7 PID: 1215 Comm: insmod Not tainted 5.18.0-rc5-00007-g9bf578647087-dirty #10
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
RIP: 0010:load_module+0x19b/0x2391

Fixes: ec2a29593c83 ("module: harden ELF info handling")
Signed-off-by: Alexey Dobriyan <[email protected]>
---

kernel/module.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3033,6 +3033,10 @@ static int elf_validity_check(struct load_info *info)
* strings in the section safe.
*/
info->secstrings = (void *)info->hdr + strhdr->sh_offset;
+ if (strhdr->sh_size == 0) {
+ pr_err("empty section name table\n");
+ goto no_exec;
+ }
if (info->secstrings[strhdr->sh_size - 1] != '\0') {
pr_err("ELF Spec violation: section name table isn't null terminated\n");
goto no_exec;

Signed-off-by: Alexey Dobriyan <[email protected]>
---

kernel/module.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3033,6 +3033,10 @@ static int elf_validity_check(struct load_info *info)
* strings in the section safe.
*/
info->secstrings = (void *)info->hdr + strhdr->sh_offset;
+ if (strhdr->sh_size == 0) {
+ pr_err("empty section name table\n");
+ goto no_exec;
+ }
if (info->secstrings[strhdr->sh_size - 1] != '\0') {
pr_err("ELF Spec violation: section name table isn't null terminated\n");
goto no_exec;

2022-05-04 22:52:19

by Alexey Dobriyan

[permalink] [raw]

Subject: Re: [PATCH] module: fix [e_shstrndx].sh_size=0 OOB access

On Tue, May 03, 2022 at 01:15:04PM -0700, Luis Chamberlain wrote:
> On Tue, May 03, 2022 at 05:57:59PM +0300, Alexey Dobriyan wrote:
> > It is trivial to craft a module to trigger OOB access in this line:
> >
> > if (info->secstrings[strhdr->sh_size - 1] != '\0') {
> >
> > BUG: unable to handle page fault for address: ffffc90000aa0fff
> > #PF: supervisor read access in kernel mode
> > #PF: error_code(0x0000) - not-present page
> > PGD 100000067 P4D 100000067 PUD 100066067 PMD 10436f067 PTE 0
> > Oops: 0000 [#1] PREEMPT SMP PTI
> > CPU: 7 PID: 1215 Comm: insmod Not tainted 5.18.0-rc5-00007-g9bf578647087-dirty #10
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
> > RIP: 0010:load_module+0x19b/0x2391
> >
> > Signed-off-by: Alexey Dobriyan <[email protected]>
>
> Thanks! Can you resend and Cc stable?

Stable will pick it up simply because patch does apply I assume?

> This seems like an issue present for
> a long time, can you identify the commit which introduced the issue?

I thought it was ancient code but no.

2022-05-07 00:16:05

by Luis Chamberlain

[permalink] [raw]

Subject: Re: [PATCH v2] module: fix [e_shstrndx].sh_size=0 OOB access

On Wed, May 04, 2022 at 12:54:20PM +0300, Alexey Dobriyan wrote:
> It is trivial to craft a module to trigger OOB access in this line:
>
> if (info->secstrings[strhdr->sh_size - 1] != '\0') {
>
> BUG: unable to handle page fault for address: ffffc90000aa0fff
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 100000067 P4D 100000067 PUD 100066067 PMD 10436f067 PTE 0
> Oops: 0000 [#1] PREEMPT SMP PTI
> CPU: 7 PID: 1215 Comm: insmod Not tainted 5.18.0-rc5-00007-g9bf578647087-dirty #10
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014
> RIP: 0010:load_module+0x19b/0x2391
>
> Fixes: ec2a29593c83 ("module: harden ELF info handling")
> Signed-off-by: Alexey Dobriyan <[email protected]>

Thanks! I rebased your patch onto modules-next [0] and applied onto
modules-testing and pushed out there. If that doesn't break I'll then
push to modules-next as well.

Luis