[PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[Gaosheng Cui]

Shifting signed 32-bit value by 31 bits is undefined, so changing
significant bit to unsigned. The UBSAN warning calltrace like below:

UBSAN: shift-out-of-bounds in security/commoncap.c:1252:2
left shift of 1 by 31 places cannot be represented in type 'int'
Call Trace:
 <TASK>
 dump_stack_lvl+0x7d/0xa5
 dump_stack+0x15/0x1b
 ubsan_epilogue+0xe/0x4e
 __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
 cap_task_prctl+0x561/0x6f0
 security_task_prctl+0x5a/0xb0
 __x64_sys_prctl+0x61/0x8f0
 do_syscall_64+0x58/0x80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 </TASK>

Fixes: e338d263a76a ("Add 64-bit capability support to the kernel")
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
---
 include/uapi/linux/capability.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
index 463d1ba2232a..3d61a0ae055d 100644
--- a/include/uapi/linux/capability.h
+++ b/include/uapi/linux/capability.h
@@ -426,7 +426,7 @@ struct vfs_ns_cap_data {
  */
 
 #define CAP_TO_INDEX(x)     ((x) >> 5)        /* 1 << 5 == bits in __u32 */
-#define CAP_TO_MASK(x)      (1 << ((x) & 31)) /* mask for indexed __u32 */
+#define CAP_TO_MASK(x)      (1U << ((x) & 31)) /* mask for indexed __u32 */
 
 
 #endif /* _UAPI_LINUX_CAPABILITY_H */
-- 
2.25.1

Re: [PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[Andrew G. Morgan]

Acked-by: Andrew G. Morgan <morgan@kernel.org>


On Mon, Oct 31, 2022 at 4:25 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
>
> Shifting signed 32-bit value by 31 bits is undefined, so changing
> significant bit to unsigned. The UBSAN warning calltrace like below:
>
> UBSAN: shift-out-of-bounds in security/commoncap.c:1252:2
> left shift of 1 by 31 places cannot be represented in type 'int'
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x7d/0xa5
>  dump_stack+0x15/0x1b
>  ubsan_epilogue+0xe/0x4e
>  __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
>  cap_task_prctl+0x561/0x6f0
>  security_task_prctl+0x5a/0xb0
>  __x64_sys_prctl+0x61/0x8f0
>  do_syscall_64+0x58/0x80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>  </TASK>
>
> Fixes: e338d263a76a ("Add 64-bit capability support to the kernel")
> Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
> ---
>  include/uapi/linux/capability.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> index 463d1ba2232a..3d61a0ae055d 100644
> --- a/include/uapi/linux/capability.h
> +++ b/include/uapi/linux/capability.h
> @@ -426,7 +426,7 @@ struct vfs_ns_cap_data {
>   */
>
>  #define CAP_TO_INDEX(x)     ((x) >> 5)        /* 1 << 5 == bits in __u32 */
> -#define CAP_TO_MASK(x)      (1 << ((x) & 31)) /* mask for indexed __u32 */
> +#define CAP_TO_MASK(x)      (1U << ((x) & 31)) /* mask for indexed __u32 */
>
>
>  #endif /* _UAPI_LINUX_CAPABILITY_H */
> --
> 2.25.1
>

Re: [PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[Serge E. Hallyn]

On Mon, Oct 31, 2022 at 07:18:54AM -0700, Andrew G. Morgan wrote:
> Acked-by: Andrew G. Morgan <morgan@kernel.org>
> 
> 
> On Mon, Oct 31, 2022 at 4:25 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
> >
> > Shifting signed 32-bit value by 31 bits is undefined, so changing
> > significant bit to unsigned. The UBSAN warning calltrace like below:
> >
> > UBSAN: shift-out-of-bounds in security/commoncap.c:1252:2
> > left shift of 1 by 31 places cannot be represented in type 'int'
> > Call Trace:
> >  <TASK>
> >  dump_stack_lvl+0x7d/0xa5
> >  dump_stack+0x15/0x1b
> >  ubsan_epilogue+0xe/0x4e
> >  __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
> >  cap_task_prctl+0x561/0x6f0
> >  security_task_prctl+0x5a/0xb0
> >  __x64_sys_prctl+0x61/0x8f0
> >  do_syscall_64+0x58/0x80
> >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> >  </TASK>
> >
> > Fixes: e338d263a76a ("Add 64-bit capability support to the kernel")
> > Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>

Reviewed-by: Serge Hallyn <serge@hallyn.com>

Paul, do you mind including this in your lsm tree?

thanks,
-serge

> > ---
> >  include/uapi/linux/capability.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> > index 463d1ba2232a..3d61a0ae055d 100644
> > --- a/include/uapi/linux/capability.h
> > +++ b/include/uapi/linux/capability.h
> > @@ -426,7 +426,7 @@ struct vfs_ns_cap_data {
> >   */
> >
> >  #define CAP_TO_INDEX(x)     ((x) >> 5)        /* 1 << 5 == bits in __u32 */
> > -#define CAP_TO_MASK(x)      (1 << ((x) & 31)) /* mask for indexed __u32 */
> > +#define CAP_TO_MASK(x)      (1U << ((x) & 31)) /* mask for indexed __u32 */
> >
> >
> >  #endif /* _UAPI_LINUX_CAPABILITY_H */
> > --
> > 2.25.1
> >

Re: [PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[Paul Moore]

On Tue, Nov 1, 2022 at 12:30 AM Serge E. Hallyn <serge@hallyn.com> wrote:
> On Mon, Oct 31, 2022 at 07:18:54AM -0700, Andrew G. Morgan wrote:
> > Acked-by: Andrew G. Morgan <morgan@kernel.org>
> >
> >
> > On Mon, Oct 31, 2022 at 4:25 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
> > >
> > > Shifting signed 32-bit value by 31 bits is undefined, so changing
> > > significant bit to unsigned. The UBSAN warning calltrace like below:
> > >
> > > UBSAN: shift-out-of-bounds in security/commoncap.c:1252:2
> > > left shift of 1 by 31 places cannot be represented in type 'int'
> > > Call Trace:
> > >  <TASK>
> > >  dump_stack_lvl+0x7d/0xa5
> > >  dump_stack+0x15/0x1b
> > >  ubsan_epilogue+0xe/0x4e
> > >  __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
> > >  cap_task_prctl+0x561/0x6f0
> > >  security_task_prctl+0x5a/0xb0
> > >  __x64_sys_prctl+0x61/0x8f0
> > >  do_syscall_64+0x58/0x80
> > >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > >  </TASK>
> > >
> > > Fixes: e338d263a76a ("Add 64-bit capability support to the kernel")
> > > Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
>
> Reviewed-by: Serge Hallyn <serge@hallyn.com>
>
> Paul, do you mind including this in your lsm tree?

Sure, although just a warning that it might not happen until next
week.  Maybe I'll get some time this weekend but I can't be certain.

> > > ---
> > >  include/uapi/linux/capability.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/uapi/linux/capability.h b/include/uapi/linux/capability.h
> > > index 463d1ba2232a..3d61a0ae055d 100644
> > > --- a/include/uapi/linux/capability.h
> > > +++ b/include/uapi/linux/capability.h
> > > @@ -426,7 +426,7 @@ struct vfs_ns_cap_data {
> > >   */
> > >
> > >  #define CAP_TO_INDEX(x)     ((x) >> 5)        /* 1 << 5 == bits in __u32 */
> > > -#define CAP_TO_MASK(x)      (1 << ((x) & 31)) /* mask for indexed __u32 */
> > > +#define CAP_TO_MASK(x)      (1U << ((x) & 31)) /* mask for indexed __u32 */
> > >
> > >
> > >  #endif /* _UAPI_LINUX_CAPABILITY_H */
> > > --
> > > 2.25.1

-- 
paul-moore.com

Re: [PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[Serge E. Hallyn]

On Thu, Nov 03, 2022 at 07:57:45AM -0400, Paul Moore wrote:
> On Tue, Nov 1, 2022 at 12:30 AM Serge E. Hallyn <serge@hallyn.com> wrote:
> > On Mon, Oct 31, 2022 at 07:18:54AM -0700, Andrew G. Morgan wrote:
> > > Acked-by: Andrew G. Morgan <morgan@kernel.org>
> > >
> > >
> > > On Mon, Oct 31, 2022 at 4:25 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
> > > >
> > > > Shifting signed 32-bit value by 31 bits is undefined, so changing
> > > > significant bit to unsigned. The UBSAN warning calltrace like below:
> > > >
> > > > UBSAN: shift-out-of-bounds in security/commoncap.c:1252:2
> > > > left shift of 1 by 31 places cannot be represented in type 'int'
> > > > Call Trace:
> > > >  <TASK>
> > > >  dump_stack_lvl+0x7d/0xa5
> > > >  dump_stack+0x15/0x1b
> > > >  ubsan_epilogue+0xe/0x4e
> > > >  __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
> > > >  cap_task_prctl+0x561/0x6f0
> > > >  security_task_prctl+0x5a/0xb0
> > > >  __x64_sys_prctl+0x61/0x8f0
> > > >  do_syscall_64+0x58/0x80
> > > >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > > >  </TASK>
> > > >
> > > > Fixes: e338d263a76a ("Add 64-bit capability support to the kernel")
> > > > Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
> >
> > Reviewed-by: Serge Hallyn <serge@hallyn.com>
> >
> > Paul, do you mind including this in your lsm tree?
> 
> Sure, although just a warning that it might not happen until next
> week.  Maybe I'll get some time this weekend but I can't be certain.

Ok, thanks.

I wouldn't mind putting up a capability tree if number of patches were
going to start ramping up, but historically that has not been worth it.

Re: [PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[Paul Moore]

On Thu, Nov 3, 2022 at 9:24 AM Serge E. Hallyn <serge@hallyn.com> wrote:
> Ok, thanks.
>
> I wouldn't mind putting up a capability tree if number of patches were
> going to start ramping up, but historically that has not been worth it.

Don't ever let me stop you from setting up a capability tree, but
yeah, I understand why it probably wouldn't be very useful.  As long
as you keep doing the reviews, ACKs, etc. I don't mind carrying the
capability patches in the LSM tree; merging stuff is usually the easy
part of the job.

-- 
paul-moore.com

Re: [PATCH] capabilities: fix undefined behavior in bit shift for CAP_TO_MASK

[Paul Moore]

On Mon, Oct 31, 2022 at 7:25 AM Gaosheng Cui <cuigaosheng1@huawei.com> wrote:
>
> Shifting signed 32-bit value by 31 bits is undefined, so changing
> significant bit to unsigned. The UBSAN warning calltrace like below:
>
> UBSAN: shift-out-of-bounds in security/commoncap.c:1252:2
> left shift of 1 by 31 places cannot be represented in type 'int'
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x7d/0xa5
>  dump_stack+0x15/0x1b
>  ubsan_epilogue+0xe/0x4e
>  __ubsan_handle_shift_out_of_bounds+0x1e7/0x20c
>  cap_task_prctl+0x561/0x6f0
>  security_task_prctl+0x5a/0xb0
>  __x64_sys_prctl+0x61/0x8f0
>  do_syscall_64+0x58/0x80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
>  </TASK>
>
> Fixes: e338d263a76a ("Add 64-bit capability support to the kernel")
> Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
> ---
>  include/uapi/linux/capability.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Merged into lsm/stable-6.1, and I'll plan to send this up to Linus
next week.  Thanks everyone!

-- 
paul-moore.com