Re: [PATCH] swapfile: fix memory corruption via malformed swapfile

[Johannes Weiner]

On Mon, Oct 31, 2016 at 10:32:13PM +0100, Jann Horn wrote:
> When root activates a swap partition whose header has the wrong endianness,
> nr_badpages elements of badpages are swabbed before nr_badpages has been
> checked, leading to a buffer overrun of up to 8GB.
> 
> This normally is not a security issue because it can only be exploited by
> root (more specifically, a process with CAP_SYS_ADMIN or the ability to
> modify a swap file/partition), and such a process can already e.g. modify
> swapped-out memory of any other userspace process on the system.
> 
> Testcase for reproducing the bug (must be run as root, should crash your
> kernel):
[...]
> Cc: sta...@vger.kernel.org
> Signed-off-by: Jann Horn 

Acked-by: Johannes Weiner 

Re: [PATCH] swapfile: fix memory corruption via malformed swapfile

[Johannes Weiner]

On Mon, Oct 31, 2016 at 10:32:13PM +0100, Jann Horn wrote:
> When root activates a swap partition whose header has the wrong endianness,
> nr_badpages elements of badpages are swabbed before nr_badpages has been
> checked, leading to a buffer overrun of up to 8GB.
> 
> This normally is not a security issue because it can only be exploited by
> root (more specifically, a process with CAP_SYS_ADMIN or the ability to
> modify a swap file/partition), and such a process can already e.g. modify
> swapped-out memory of any other userspace process on the system.
> 
> Testcase for reproducing the bug (must be run as root, should crash your
> kernel):
[...]
> Cc: sta...@vger.kernel.org
> Signed-off-by: Jann Horn 

Acked-by: Johannes Weiner 

Re: [PATCH] swapfile: fix memory corruption via malformed swapfile

[Jerome Marchand]

On 10/31/2016 10:32 PM, Jann Horn wrote:
> When root activates a swap partition whose header has the wrong endianness,
> nr_badpages elements of badpages are swabbed before nr_badpages has been
> checked, leading to a buffer overrun of up to 8GB.
> 
> This normally is not a security issue because it can only be exploited by
> root (more specifically, a process with CAP_SYS_ADMIN or the ability to
> modify a swap file/partition), and such a process can already e.g. modify
> swapped-out memory of any other userspace process on the system.
> 
> Testcase for reproducing the bug (must be run as root, should crash your
> kernel):
> =
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
> 
> #define PAGE_SIZE 4096
> #define __u32 unsigned int
> 
> 
> // from include/linux/swap.h
> union swap_header {
>   struct {
> char reserved[PAGE_SIZE - 10];
> char magic[10]; /* SWAP-SPACE or SWAPSPACE2 */
>   } magic;
>   struct {
> charbootbits[1024]; /* Space for disklabel etc. */
> __u32   version;
> __u32   last_page;
> __u32   nr_badpages;
> unsigned char sws_uuid[16];
> unsigned char sws_volume[16];
> __u32   padding[117];
> __u32   badpages[1];
>   } info;
> };
> 
> int main(void) {
>   char file[] = "/tmp/swapfile.XX";
>   int file_fd = mkstemp(file);
>   if (file_fd == -1)
> err(1, "mkstemp");
>   if (ftruncate(file_fd, PAGE_SIZE))
> err(1, "ftruncate");
>   union swap_header swap_header = {
> .info = {
>   .version = __builtin_bswap32(1),
>   .nr_badpages = __builtin_bswap32(INT_MAX)
> }
>   };
>   memcpy(swap_header.magic.magic, "SWAPSPACE2", 10);
>   if (write(file_fd, _header, sizeof(swap_header)) !=
>   sizeof(swap_header))
> err(1, "write");
> 
>   // not because the attack needs it, just in case you forgot to
>   // sync yourself before crashing your machine
>   sync();
> 
>   // now die
>   if (swapon(file, 0))
> err(1, "swapon");
>   puts("huh, we survived");
>   if (swapoff(file))
> err(1, "swapoff");
>   unlink(file);
> }
> =
> 
> Cc: sta...@vger.kernel.org
> Signed-off-by: Jann Horn 
> ---
>  mm/swapfile.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 2210de290b54..f30438970cd1 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2224,6 +2224,8 @@ static unsigned long read_swap_header(struct 
> swap_info_struct *p,
>   swab32s(_header->info.version);
>   swab32s(_header->info.last_page);
>   swab32s(_header->info.nr_badpages);
> + if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
> + return 0;
>   for (i = 0; i < swap_header->info.nr_badpages; i++)
>   swab32s(_header->info.badpages[i]);
>   }
> 

Nice catch!

Acked-by: Jerome Marchand 





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Re: [PATCH] swapfile: fix memory corruption via malformed swapfile

[Jerome Marchand]

On 10/31/2016 10:32 PM, Jann Horn wrote:
> When root activates a swap partition whose header has the wrong endianness,
> nr_badpages elements of badpages are swabbed before nr_badpages has been
> checked, leading to a buffer overrun of up to 8GB.
> 
> This normally is not a security issue because it can only be exploited by
> root (more specifically, a process with CAP_SYS_ADMIN or the ability to
> modify a swap file/partition), and such a process can already e.g. modify
> swapped-out memory of any other userspace process on the system.
> 
> Testcase for reproducing the bug (must be run as root, should crash your
> kernel):
> =
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
> 
> #define PAGE_SIZE 4096
> #define __u32 unsigned int
> 
> 
> // from include/linux/swap.h
> union swap_header {
>   struct {
> char reserved[PAGE_SIZE - 10];
> char magic[10]; /* SWAP-SPACE or SWAPSPACE2 */
>   } magic;
>   struct {
> charbootbits[1024]; /* Space for disklabel etc. */
> __u32   version;
> __u32   last_page;
> __u32   nr_badpages;
> unsigned char sws_uuid[16];
> unsigned char sws_volume[16];
> __u32   padding[117];
> __u32   badpages[1];
>   } info;
> };
> 
> int main(void) {
>   char file[] = "/tmp/swapfile.XX";
>   int file_fd = mkstemp(file);
>   if (file_fd == -1)
> err(1, "mkstemp");
>   if (ftruncate(file_fd, PAGE_SIZE))
> err(1, "ftruncate");
>   union swap_header swap_header = {
> .info = {
>   .version = __builtin_bswap32(1),
>   .nr_badpages = __builtin_bswap32(INT_MAX)
> }
>   };
>   memcpy(swap_header.magic.magic, "SWAPSPACE2", 10);
>   if (write(file_fd, _header, sizeof(swap_header)) !=
>   sizeof(swap_header))
> err(1, "write");
> 
>   // not because the attack needs it, just in case you forgot to
>   // sync yourself before crashing your machine
>   sync();
> 
>   // now die
>   if (swapon(file, 0))
> err(1, "swapon");
>   puts("huh, we survived");
>   if (swapoff(file))
> err(1, "swapoff");
>   unlink(file);
> }
> =
> 
> Cc: sta...@vger.kernel.org
> Signed-off-by: Jann Horn 
> ---
>  mm/swapfile.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 2210de290b54..f30438970cd1 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2224,6 +2224,8 @@ static unsigned long read_swap_header(struct 
> swap_info_struct *p,
>   swab32s(_header->info.version);
>   swab32s(_header->info.last_page);
>   swab32s(_header->info.nr_badpages);
> + if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
> + return 0;
>   for (i = 0; i < swap_header->info.nr_badpages; i++)
>   swab32s(_header->info.badpages[i]);
>   }
> 

Nice catch!

Acked-by: Jerome Marchand 





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Re: [PATCH] swapfile: fix memory corruption via malformed swapfile

[Kees Cook]

On Mon, Oct 31, 2016 at 2:32 PM, Jann Horn  wrote:
> When root activates a swap partition whose header has the wrong endianness,
> nr_badpages elements of badpages are swabbed before nr_badpages has been
> checked, leading to a buffer overrun of up to 8GB.
>
> This normally is not a security issue because it can only be exploited by
> root (more specifically, a process with CAP_SYS_ADMIN or the ability to
> modify a swap file/partition), and such a process can already e.g. modify
> swapped-out memory of any other userspace process on the system.
>
> Testcase for reproducing the bug (must be run as root, should crash your
> kernel):
> =
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
>
> #define PAGE_SIZE 4096
> #define __u32 unsigned int
>
>
> // from include/linux/swap.h
> union swap_header {
>   struct {
> char reserved[PAGE_SIZE - 10];
> char magic[10]; /* SWAP-SPACE or SWAPSPACE2 */
>   } magic;
>   struct {
> charbootbits[1024]; /* Space for disklabel etc. */
> __u32   version;
> __u32   last_page;
> __u32   nr_badpages;
> unsigned char sws_uuid[16];
> unsigned char sws_volume[16];
> __u32   padding[117];
> __u32   badpages[1];
>   } info;
> };
>
> int main(void) {
>   char file[] = "/tmp/swapfile.XX";
>   int file_fd = mkstemp(file);
>   if (file_fd == -1)
> err(1, "mkstemp");
>   if (ftruncate(file_fd, PAGE_SIZE))
> err(1, "ftruncate");
>   union swap_header swap_header = {
> .info = {
>   .version = __builtin_bswap32(1),
>   .nr_badpages = __builtin_bswap32(INT_MAX)
> }
>   };
>   memcpy(swap_header.magic.magic, "SWAPSPACE2", 10);
>   if (write(file_fd, _header, sizeof(swap_header)) !=
>   sizeof(swap_header))
> err(1, "write");
>
>   // not because the attack needs it, just in case you forgot to
>   // sync yourself before crashing your machine
>   sync();
>
>   // now die
>   if (swapon(file, 0))
> err(1, "swapon");
>   puts("huh, we survived");
>   if (swapoff(file))
> err(1, "swapoff");
>   unlink(file);
> }
> =
>
> Cc: sta...@vger.kernel.org
> Signed-off-by: Jann Horn 
> ---
>  mm/swapfile.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 2210de290b54..f30438970cd1 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2224,6 +2224,8 @@ static unsigned long read_swap_header(struct 
> swap_info_struct *p,
> swab32s(_header->info.version);
> swab32s(_header->info.last_page);
> swab32s(_header->info.nr_badpages);
> +   if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
> +   return 0;
> for (i = 0; i < swap_header->info.nr_badpages; i++)
> swab32s(_header->info.badpages[i]);
> }
> --
> 2.1.4
>

Eww. Nice find. :) At least it's only init_ns CAP_SYS_ADMIN. :P

Acked-by: Kees Cook 

-Kees

-- 
Kees Cook
Nexus Security

Re: [PATCH] swapfile: fix memory corruption via malformed swapfile

[Kees Cook]

On Mon, Oct 31, 2016 at 2:32 PM, Jann Horn  wrote:
> When root activates a swap partition whose header has the wrong endianness,
> nr_badpages elements of badpages are swabbed before nr_badpages has been
> checked, leading to a buffer overrun of up to 8GB.
>
> This normally is not a security issue because it can only be exploited by
> root (more specifically, a process with CAP_SYS_ADMIN or the ability to
> modify a swap file/partition), and such a process can already e.g. modify
> swapped-out memory of any other userspace process on the system.
>
> Testcase for reproducing the bug (must be run as root, should crash your
> kernel):
> =
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
> #include 
>
> #define PAGE_SIZE 4096
> #define __u32 unsigned int
>
>
> // from include/linux/swap.h
> union swap_header {
>   struct {
> char reserved[PAGE_SIZE - 10];
> char magic[10]; /* SWAP-SPACE or SWAPSPACE2 */
>   } magic;
>   struct {
> charbootbits[1024]; /* Space for disklabel etc. */
> __u32   version;
> __u32   last_page;
> __u32   nr_badpages;
> unsigned char sws_uuid[16];
> unsigned char sws_volume[16];
> __u32   padding[117];
> __u32   badpages[1];
>   } info;
> };
>
> int main(void) {
>   char file[] = "/tmp/swapfile.XX";
>   int file_fd = mkstemp(file);
>   if (file_fd == -1)
> err(1, "mkstemp");
>   if (ftruncate(file_fd, PAGE_SIZE))
> err(1, "ftruncate");
>   union swap_header swap_header = {
> .info = {
>   .version = __builtin_bswap32(1),
>   .nr_badpages = __builtin_bswap32(INT_MAX)
> }
>   };
>   memcpy(swap_header.magic.magic, "SWAPSPACE2", 10);
>   if (write(file_fd, _header, sizeof(swap_header)) !=
>   sizeof(swap_header))
> err(1, "write");
>
>   // not because the attack needs it, just in case you forgot to
>   // sync yourself before crashing your machine
>   sync();
>
>   // now die
>   if (swapon(file, 0))
> err(1, "swapon");
>   puts("huh, we survived");
>   if (swapoff(file))
> err(1, "swapoff");
>   unlink(file);
> }
> =
>
> Cc: sta...@vger.kernel.org
> Signed-off-by: Jann Horn 
> ---
>  mm/swapfile.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 2210de290b54..f30438970cd1 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -2224,6 +2224,8 @@ static unsigned long read_swap_header(struct 
> swap_info_struct *p,
> swab32s(_header->info.version);
> swab32s(_header->info.last_page);
> swab32s(_header->info.nr_badpages);
> +   if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
> +   return 0;
> for (i = 0; i < swap_header->info.nr_badpages; i++)
> swab32s(_header->info.badpages[i]);
> }
> --
> 2.1.4
>

Eww. Nice find. :) At least it's only init_ns CAP_SYS_ADMIN. :P

Acked-by: Kees Cook 

-Kees

-- 
Kees Cook
Nexus Security

[PATCH] swapfile: fix memory corruption via malformed swapfile

[Jann Horn]

When root activates a swap partition whose header has the wrong endianness,
nr_badpages elements of badpages are swabbed before nr_badpages has been
checked, leading to a buffer overrun of up to 8GB.

This normally is not a security issue because it can only be exploited by
root (more specifically, a process with CAP_SYS_ADMIN or the ability to
modify a swap file/partition), and such a process can already e.g. modify
swapped-out memory of any other userspace process on the system.

Testcase for reproducing the bug (must be run as root, should crash your
kernel):
=
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define PAGE_SIZE 4096
#define __u32 unsigned int


// from include/linux/swap.h
union swap_header {
  struct {
char reserved[PAGE_SIZE - 10];
char magic[10]; /* SWAP-SPACE or SWAPSPACE2 */
  } magic;
  struct {
charbootbits[1024]; /* Space for disklabel etc. */
__u32   version;
__u32   last_page;
__u32   nr_badpages;
unsigned char sws_uuid[16];
unsigned char sws_volume[16];
__u32   padding[117];
__u32   badpages[1];
  } info;
};

int main(void) {
  char file[] = "/tmp/swapfile.XX";
  int file_fd = mkstemp(file);
  if (file_fd == -1)
err(1, "mkstemp");
  if (ftruncate(file_fd, PAGE_SIZE))
err(1, "ftruncate");
  union swap_header swap_header = {
.info = {
  .version = __builtin_bswap32(1),
  .nr_badpages = __builtin_bswap32(INT_MAX)
}
  };
  memcpy(swap_header.magic.magic, "SWAPSPACE2", 10);
  if (write(file_fd, _header, sizeof(swap_header)) !=
  sizeof(swap_header))
err(1, "write");

  // not because the attack needs it, just in case you forgot to
  // sync yourself before crashing your machine
  sync();

  // now die
  if (swapon(file, 0))
err(1, "swapon");
  puts("huh, we survived");
  if (swapoff(file))
err(1, "swapoff");
  unlink(file);
}
=

Cc: sta...@vger.kernel.org
Signed-off-by: Jann Horn 
---
 mm/swapfile.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2210de290b54..f30438970cd1 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2224,6 +2224,8 @@ static unsigned long read_swap_header(struct 
swap_info_struct *p,
swab32s(_header->info.version);
swab32s(_header->info.last_page);
swab32s(_header->info.nr_badpages);
+   if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+   return 0;
for (i = 0; i < swap_header->info.nr_badpages; i++)
swab32s(_header->info.badpages[i]);
}
-- 
2.1.4

[PATCH] swapfile: fix memory corruption via malformed swapfile

[Jann Horn]

When root activates a swap partition whose header has the wrong endianness,
nr_badpages elements of badpages are swabbed before nr_badpages has been
checked, leading to a buffer overrun of up to 8GB.

This normally is not a security issue because it can only be exploited by
root (more specifically, a process with CAP_SYS_ADMIN or the ability to
modify a swap file/partition), and such a process can already e.g. modify
swapped-out memory of any other userspace process on the system.

Testcase for reproducing the bug (must be run as root, should crash your
kernel):
=
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define PAGE_SIZE 4096
#define __u32 unsigned int


// from include/linux/swap.h
union swap_header {
  struct {
char reserved[PAGE_SIZE - 10];
char magic[10]; /* SWAP-SPACE or SWAPSPACE2 */
  } magic;
  struct {
charbootbits[1024]; /* Space for disklabel etc. */
__u32   version;
__u32   last_page;
__u32   nr_badpages;
unsigned char sws_uuid[16];
unsigned char sws_volume[16];
__u32   padding[117];
__u32   badpages[1];
  } info;
};

int main(void) {
  char file[] = "/tmp/swapfile.XX";
  int file_fd = mkstemp(file);
  if (file_fd == -1)
err(1, "mkstemp");
  if (ftruncate(file_fd, PAGE_SIZE))
err(1, "ftruncate");
  union swap_header swap_header = {
.info = {
  .version = __builtin_bswap32(1),
  .nr_badpages = __builtin_bswap32(INT_MAX)
}
  };
  memcpy(swap_header.magic.magic, "SWAPSPACE2", 10);
  if (write(file_fd, _header, sizeof(swap_header)) !=
  sizeof(swap_header))
err(1, "write");

  // not because the attack needs it, just in case you forgot to
  // sync yourself before crashing your machine
  sync();

  // now die
  if (swapon(file, 0))
err(1, "swapon");
  puts("huh, we survived");
  if (swapoff(file))
err(1, "swapoff");
  unlink(file);
}
=

Cc: sta...@vger.kernel.org
Signed-off-by: Jann Horn 
---
 mm/swapfile.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 2210de290b54..f30438970cd1 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2224,6 +2224,8 @@ static unsigned long read_swap_header(struct 
swap_info_struct *p,
swab32s(_header->info.version);
swab32s(_header->info.last_page);
swab32s(_header->info.nr_badpages);
+   if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
+   return 0;
for (i = 0; i < swap_header->info.nr_badpages; i++)
swab32s(_header->info.badpages[i]);
}
-- 
2.1.4