[PATCH v2 0/2] fix parsing of reboot= cmdline

[PATCH v2 0/2] fix parsing of reboot= cmdline

[Matteo Croce]

From: Matteo Croce <mcroce@microsoft.com>

The parsing of the reboot= cmdline has two major errors:
- a missing bound check can crash the system on reboot
- parsing of the cpu number only works if specified last

Fix both, along with a small code refactor.

v1->v2:
As Petr suggested, don't force base 10 in simple_strtoul(),
so hex values are accepted as well.

Matteo Croce (2):
  reboot: fix overflow parsing reboot cpu number
  reboot: fix parsing of reboot cpu number

 kernel/reboot.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

-- 
2.28.0

[PATCH v2 1/2] reboot: fix overflow parsing reboot cpu number

[Matteo Croce]

From: Matteo Croce <mcroce@microsoft.com>

Limit the CPU number to num_possible_cpus(), because setting it
to a value lower than INT_MAX but higher than NR_CPUS produces the
following error on reboot and shutdown:

    BUG: unable to handle page fault for address: ffffffff90ab1bb0
    #PF: supervisor read access in kernel mode
    #PF: error_code(0x0000) - not-present page
    PGD 1c09067 P4D 1c09067 PUD 1c0a063 PMD 0
    Oops: 0000 [#1] SMP
    CPU: 1 PID: 1 Comm: systemd-shutdow Not tainted 5.9.0-rc8-kvm #110
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
    RIP: 0010:migrate_to_reboot_cpu+0xe/0x60
    Code: ea ea 00 48 89 fa 48 c7 c7 30 57 f1 81 e9 fa ef ff ff 66 2e 0f 1f 84 00 00 00 00 00 53 8b 1d d5 ea ea 00 e8 14 33 fe ff 89 da <48> 0f a3 15 ea fc bd 00 48 89 d0 73 29 89 c2 c1 e8 06 65 48 8b 3c
    RSP: 0018:ffffc90000013e08 EFLAGS: 00010246
    RAX: ffff88801f0a0000 RBX: 0000000077359400 RCX: 0000000000000000
    RDX: 0000000077359400 RSI: 0000000000000002 RDI: ffffffff81c199e0
    RBP: ffffffff81c1e3c0 R08: ffff88801f41f000 R09: ffffffff81c1e348
    R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
    R13: 00007f32bedf8830 R14: 00000000fee1dead R15: 0000000000000000
    FS:  00007f32bedf8980(0000) GS:ffff88801f480000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: ffffffff90ab1bb0 CR3: 000000001d057000 CR4: 00000000000006a0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:
    __do_sys_reboot.cold+0x34/0x5b
    ? vfs_writev+0x92/0xc0
    ? do_writev+0x52/0xd0
    do_syscall_64+0x2d/0x40
    entry_SYSCALL_64_after_hwframe+0x44/0xa9
    RIP: 0033:0x7f32bfaaecd3
    Code: 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 89 fa be 69 19 12 28 bf ad de e1 fe b8 a9 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 05 c3 0f 1f 40 00 48 8b 15 89 81 0c 00 f7 d8
    RSP: 002b:00007fff6265fb58 EFLAGS: 00000202 ORIG_RAX: 00000000000000a9
    RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f32bfaaecd3
    RDX: 0000000001234567 RSI: 0000000028121969 RDI: 00000000fee1dead
    RBP: 0000000000000000 R08: 0000000000008020 R09: 00007fff6265ef60
    R10: 00007f32bedf8830 R11: 0000000000000202 R12: 0000000000000000
    R13: 0000557bba2c51c0 R14: 0000000000000000 R15: 00007fff6265fbc8
    CR2: ffffffff90ab1bb0
    ---[ end trace b813e80157136563 ]---
    RIP: 0010:migrate_to_reboot_cpu+0xe/0x60
    Code: ea ea 00 48 89 fa 48 c7 c7 30 57 f1 81 e9 fa ef ff ff 66 2e 0f 1f 84 00 00 00 00 00 53 8b 1d d5 ea ea 00 e8 14 33 fe ff 89 da <48> 0f a3 15 ea fc bd 00 48 89 d0 73 29 89 c2 c1 e8 06 65 48 8b 3c
    RSP: 0018:ffffc90000013e08 EFLAGS: 00010246
    RAX: ffff88801f0a0000 RBX: 0000000077359400 RCX: 0000000000000000
    RDX: 0000000077359400 RSI: 0000000000000002 RDI: ffffffff81c199e0
    RBP: ffffffff81c1e3c0 R08: ffff88801f41f000 R09: ffffffff81c1e348
    R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
    R13: 00007f32bedf8830 R14: 00000000fee1dead R15: 0000000000000000
    FS:  00007f32bedf8980(0000) GS:ffff88801f480000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: ffffffff90ab1bb0 CR3: 000000001d057000 CR4: 00000000000006a0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
    Kernel Offset: disabled
    ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009 ]---

Fixes: 1b3a5d02ee07 ("reboot: move arch/x86 reboot= handling to generic kernel")
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
---
 kernel/reboot.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index e7b78d5ae1ab..c4e7965c39b9 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -558,11 +558,19 @@ static int __init reboot_setup(char *str)
 				rc = kstrtoint(str+1, 0, &reboot_cpu);
 				if (rc)
 					return rc;
+				if (reboot_cpu >= num_possible_cpus()) {
+					reboot_cpu = 0;
+					return -ERANGE;
+				}
 			} else if (str[1] == 'm' && str[2] == 'p' &&
 				   isdigit(*(str+3))) {
 				rc = kstrtoint(str+3, 0, &reboot_cpu);
 				if (rc)
 					return rc;
+				if (reboot_cpu >= num_possible_cpus()) {
+					reboot_cpu = 0;
+					return -ERANGE;
+				}
 			} else
 				*mode = REBOOT_SOFT;
 			break;
-- 
2.28.0

Re: [PATCH v2 1/2] reboot: fix overflow parsing reboot cpu number

[Greg KH]

On Tue, Oct 27, 2020 at 02:35:44PM +0100, Matteo Croce wrote:
> From: Matteo Croce <mcroce@microsoft.com>
> 
> Limit the CPU number to num_possible_cpus(), because setting it
> to a value lower than INT_MAX but higher than NR_CPUS produces the
> following error on reboot and shutdown:
> 
>     BUG: unable to handle page fault for address: ffffffff90ab1bb0
>     #PF: supervisor read access in kernel mode
>     #PF: error_code(0x0000) - not-present page
>     PGD 1c09067 P4D 1c09067 PUD 1c0a063 PMD 0
>     Oops: 0000 [#1] SMP
>     CPU: 1 PID: 1 Comm: systemd-shutdow Not tainted 5.9.0-rc8-kvm #110
>     Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
>     RIP: 0010:migrate_to_reboot_cpu+0xe/0x60
>     Code: ea ea 00 48 89 fa 48 c7 c7 30 57 f1 81 e9 fa ef ff ff 66 2e 0f 1f 84 00 00 00 00 00 53 8b 1d d5 ea ea 00 e8 14 33 fe ff 89 da <48> 0f a3 15 ea fc bd 00 48 89 d0 73 29 89 c2 c1 e8 06 65 48 8b 3c
>     RSP: 0018:ffffc90000013e08 EFLAGS: 00010246
>     RAX: ffff88801f0a0000 RBX: 0000000077359400 RCX: 0000000000000000
>     RDX: 0000000077359400 RSI: 0000000000000002 RDI: ffffffff81c199e0
>     RBP: ffffffff81c1e3c0 R08: ffff88801f41f000 R09: ffffffff81c1e348
>     R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>     R13: 00007f32bedf8830 R14: 00000000fee1dead R15: 0000000000000000
>     FS:  00007f32bedf8980(0000) GS:ffff88801f480000(0000) knlGS:0000000000000000
>     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>     CR2: ffffffff90ab1bb0 CR3: 000000001d057000 CR4: 00000000000006a0
>     DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>     DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>     Call Trace:
>     __do_sys_reboot.cold+0x34/0x5b
>     ? vfs_writev+0x92/0xc0
>     ? do_writev+0x52/0xd0
>     do_syscall_64+0x2d/0x40
>     entry_SYSCALL_64_after_hwframe+0x44/0xa9
>     RIP: 0033:0x7f32bfaaecd3
>     Code: 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 89 fa be 69 19 12 28 bf ad de e1 fe b8 a9 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 05 c3 0f 1f 40 00 48 8b 15 89 81 0c 00 f7 d8
>     RSP: 002b:00007fff6265fb58 EFLAGS: 00000202 ORIG_RAX: 00000000000000a9
>     RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f32bfaaecd3
>     RDX: 0000000001234567 RSI: 0000000028121969 RDI: 00000000fee1dead
>     RBP: 0000000000000000 R08: 0000000000008020 R09: 00007fff6265ef60
>     R10: 00007f32bedf8830 R11: 0000000000000202 R12: 0000000000000000
>     R13: 0000557bba2c51c0 R14: 0000000000000000 R15: 00007fff6265fbc8
>     CR2: ffffffff90ab1bb0
>     ---[ end trace b813e80157136563 ]---
>     RIP: 0010:migrate_to_reboot_cpu+0xe/0x60
>     Code: ea ea 00 48 89 fa 48 c7 c7 30 57 f1 81 e9 fa ef ff ff 66 2e 0f 1f 84 00 00 00 00 00 53 8b 1d d5 ea ea 00 e8 14 33 fe ff 89 da <48> 0f a3 15 ea fc bd 00 48 89 d0 73 29 89 c2 c1 e8 06 65 48 8b 3c
>     RSP: 0018:ffffc90000013e08 EFLAGS: 00010246
>     RAX: ffff88801f0a0000 RBX: 0000000077359400 RCX: 0000000000000000
>     RDX: 0000000077359400 RSI: 0000000000000002 RDI: ffffffff81c199e0
>     RBP: ffffffff81c1e3c0 R08: ffff88801f41f000 R09: ffffffff81c1e348
>     R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>     R13: 00007f32bedf8830 R14: 00000000fee1dead R15: 0000000000000000
>     FS:  00007f32bedf8980(0000) GS:ffff88801f480000(0000) knlGS:0000000000000000
>     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>     CR2: ffffffff90ab1bb0 CR3: 000000001d057000 CR4: 00000000000006a0
>     DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>     DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>     Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009
>     Kernel Offset: disabled
>     ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000009 ]---
> 
> Fixes: 1b3a5d02ee07 ("reboot: move arch/x86 reboot= handling to generic kernel")
> Signed-off-by: Matteo Croce <mcroce@microsoft.com>
> ---
>  kernel/reboot.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

Re: [PATCH v2 1/2] reboot: fix overflow parsing reboot cpu number

[Petr Mladek]

On Tue 2020-10-27 14:42:43, Greg KH wrote:
> On Tue, Oct 27, 2020 at 02:35:44PM +0100, Matteo Croce wrote:
> > From: Matteo Croce <mcroce@microsoft.com>
> > 
> > Limit the CPU number to num_possible_cpus(), because setting it
> > to a value lower than INT_MAX but higher than NR_CPUS produces the
> > following error on reboot and shutdown:
> > 
> > Fixes: 1b3a5d02ee07 ("reboot: move arch/x86 reboot= handling to generic kernel")
> > Signed-off-by: Matteo Croce <mcroce@microsoft.com>

Reviewed-by: Petr Mladek <pmladek@suse.com>

> <formletter>
> 
> This is not the correct way to submit patches for inclusion in the
> stable kernel tree.  Please read:
>     https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
> for how to do this properly.
> 
> </formletter>

The best way is to add the following line before Signed-off-by line:

Cc: stable@vger.kernel.org

Best Regards,
Petr

[PATCH v2 2/2] reboot: fix parsing of reboot cpu number

[Matteo Croce]

From: Matteo Croce <mcroce@microsoft.com>

The kernel cmdline reboot= argument allows to specify the CPU used
for rebooting, with the syntax `s####` among the other flags, e.g.

  reboot=soft,s4
  reboot=warm,s31,force

In the early days the parsing was done with simple_strtoul(), later
deprecated in favor of the safer kstrtoint() which handles overflow.

But kstrtoint() returns -EINVAL if there are non-digit characters
in a string, so if this flag is not the last given, it's silently
ignored as well as the subsequent ones.

To fix it, revert the usage of simple_strtoul(), which is no longer
deprecated, and restore the old behaviour.

While at it, merge two identical code blocks into one.

Fixes: 616feab75397 ("kernel/reboot.c: convert simple_strtoul to kstrtoint")
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
---
 kernel/reboot.c | 30 ++++++++++++------------------
 1 file changed, 12 insertions(+), 18 deletions(-)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index c4e7965c39b9..a09c5937c0b6 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -552,25 +552,19 @@ static int __init reboot_setup(char *str)
 
 		case 's':
 		{
-			int rc;
-
-			if (isdigit(*(str+1))) {
-				rc = kstrtoint(str+1, 0, &reboot_cpu);
-				if (rc)
-					return rc;
-				if (reboot_cpu >= num_possible_cpus()) {
-					reboot_cpu = 0;
-					return -ERANGE;
-				}
-			} else if (str[1] == 'm' && str[2] == 'p' &&
-				   isdigit(*(str+3))) {
-				rc = kstrtoint(str+3, 0, &reboot_cpu);
-				if (rc)
-					return rc;
-				if (reboot_cpu >= num_possible_cpus()) {
-					reboot_cpu = 0;
+			int cpu;
+
+			/*
+			 * reboot_cpu is s[mp]#### with #### being the processor
+			 * to be used for rebooting. Skip 's' or 'smp' prefix.
+			 */
+			str += str[1] == 'm' && str[2] == 'p' ? 3 : 1;
+
+			if (isdigit(str[0])) {
+				cpu = simple_strtoul(str, NULL, 0);
+				if (cpu >= num_possible_cpus())
 					return -ERANGE;
-				}
+				reboot_cpu = cpu;
 			} else
 				*mode = REBOOT_SOFT;
 			break;
-- 
2.28.0

Re: [PATCH v2 2/2] reboot: fix parsing of reboot cpu number

[Greg KH]

On Tue, Oct 27, 2020 at 02:35:45PM +0100, Matteo Croce wrote:
> From: Matteo Croce <mcroce@microsoft.com>
> 
> The kernel cmdline reboot= argument allows to specify the CPU used
> for rebooting, with the syntax `s####` among the other flags, e.g.
> 
>   reboot=soft,s4
>   reboot=warm,s31,force
> 
> In the early days the parsing was done with simple_strtoul(), later
> deprecated in favor of the safer kstrtoint() which handles overflow.
> 
> But kstrtoint() returns -EINVAL if there are non-digit characters
> in a string, so if this flag is not the last given, it's silently
> ignored as well as the subsequent ones.
> 
> To fix it, revert the usage of simple_strtoul(), which is no longer
> deprecated, and restore the old behaviour.
> 
> While at it, merge two identical code blocks into one.
> 
> Fixes: 616feab75397 ("kernel/reboot.c: convert simple_strtoul to kstrtoint")
> Signed-off-by: Matteo Croce <mcroce@microsoft.com>
> ---
>  kernel/reboot.c | 30 ++++++++++++------------------
>  1 file changed, 12 insertions(+), 18 deletions(-)
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>

Re: [PATCH v2 2/2] reboot: fix parsing of reboot cpu number

[Petr Mladek]

On Tue 2020-10-27 14:35:45, Matteo Croce wrote:
> From: Matteo Croce <mcroce@microsoft.com>
> 
> The kernel cmdline reboot= argument allows to specify the CPU used
> for rebooting, with the syntax `s####` among the other flags, e.g.
> 
>   reboot=soft,s4
>   reboot=warm,s31,force
> 
> In the early days the parsing was done with simple_strtoul(), later
> deprecated in favor of the safer kstrtoint() which handles overflow.
> 
> But kstrtoint() returns -EINVAL if there are non-digit characters
> in a string, so if this flag is not the last given, it's silently
> ignored as well as the subsequent ones.
> 
> To fix it, revert the usage of simple_strtoul(), which is no longer
> deprecated, and restore the old behaviour.
> 
> While at it, merge two identical code blocks into one.

> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -552,25 +552,19 @@ static int __init reboot_setup(char *str)
>  
>  		case 's':
>  		{
> -			int rc;
> -
> -			if (isdigit(*(str+1))) {
> -				rc = kstrtoint(str+1, 0, &reboot_cpu);
> -				if (rc)
> -					return rc;
> -				if (reboot_cpu >= num_possible_cpus()) {
> -					reboot_cpu = 0;
> -					return -ERANGE;
> -				}
> -			} else if (str[1] == 'm' && str[2] == 'p' &&
> -				   isdigit(*(str+3))) {
> -				rc = kstrtoint(str+3, 0, &reboot_cpu);
> -				if (rc)
> -					return rc;
> -				if (reboot_cpu >= num_possible_cpus()) {
> -					reboot_cpu = 0;

                                                     ^^^^^^

> +			int cpu;
> +
> +			/*
> +			 * reboot_cpu is s[mp]#### with #### being the processor
> +			 * to be used for rebooting. Skip 's' or 'smp' prefix.
> +			 */
> +			str += str[1] == 'm' && str[2] == 'p' ? 3 : 1;
> +
> +			if (isdigit(str[0])) {
> +				cpu = simple_strtoul(str, NULL, 0);
> +				if (cpu >= num_possible_cpus())
>  					return -ERANGE;
> -				}
> +				reboot_cpu = cpu;

The original value stays when the new one is out of range. It is
small functional change that should get mentioned in the commit
message or better fixed separately.

Hmm, I suggest to split this into 3 patches and switch the order:

  + 1st patch should simply revert the commit 616feab75397
   ("kernel/reboot.c: convert simple_strtoul to kstrtoint").

  + 2nd patch should merge the two branches without any
    functional change.

  + 3rd patch should add the check for num_possible_cpus()
    and update the value only when it is valid.

I am sorry that I did not suggested this when reviewed v1.
I have missed this functional change at that time.

Best Regards,
Petr

Re: [PATCH v2 0/2] fix parsing of reboot= cmdline

[Greg KH]

On Tue, Oct 27, 2020 at 02:35:43PM +0100, Matteo Croce wrote:
> From: Matteo Croce <mcroce@microsoft.com>
> 
> The parsing of the reboot= cmdline has two major errors:
> - a missing bound check can crash the system on reboot
> - parsing of the cpu number only works if specified last
> 
> Fix both, along with a small code refactor.
> 
> v1->v2:
> As Petr suggested, don't force base 10 in simple_strtoul(),
> so hex values are accepted as well.
> 
> Matteo Croce (2):
>   reboot: fix overflow parsing reboot cpu number
>   reboot: fix parsing of reboot cpu number
> 
>  kernel/reboot.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> -- 
> 2.28.0
> 

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>