[PATCH] get_fs_type: Validate fs type string argument

[PATCH] get_fs_type: Validate fs type string argument

[Chandan Rajendra]

On ppc64, When a non-nul terminated string is passed as an argument to
the mount(2) syscall, copy_mount_string() ends up allocating 64k (the
PAGE_SIZE on ppc64) worth of space for holding the string in kernel's
address space.

Later, in set_precision() (invoked indirectly by get_fs_type()), we end
up assigning 65535 as the value to 'struct printf_spec'->precision
member. This field has a width of 16 bits and hence a truncated version
of the original value ends up being assigned. This causes the
"WARN_ONCE(spec->precision != prec, "precision %d too large", prec)"
statement inside set_precision() to be executed.

This commit fixes the bug by validating the length of the "filesystem
type" argument passed to get_fs_type() function.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Suggested-by: Joe Perches <joe@perches.com>
---
 fs/filesystems.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/filesystems.c b/fs/filesystems.c
index a920ad2..8e309d3 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -275,6 +275,9 @@ struct file_system_type *get_fs_type(const char *name)
 	const char *dot = strchr(name, '.');
 	int len = dot ? dot - name : strlen(name);
 
+       if (len >= PATH_MAX)
+               return NULL;
+
 	fs = __get_fs_type(name, len);
 	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
 		fs = __get_fs_type(name, len);
-- 
2.9.4

[PATCH V2] get_fs_type: Validate fs type string argument

[Chandan Rajendra]

On ppc64, When a non-nul terminated string is passed as an argument to
the mount(2) syscall, copy_mount_string() ends up allocating 64k (the
PAGE_SIZE on ppc64) worth of space for holding the string in kernel's
address space.

Later, in set_precision() (invoked indirectly by get_fs_type()), we end
up assigning 65535 as the value to 'struct printf_spec'->precision
member. This field has a width of 16 bits and also it is signed data
type. Hence an invalid value ends up getting assigned. This causes the
"WARN_ONCE(spec->precision != prec, "precision %d too large", prec)"
statement inside set_precision() to be executed.

This commit fixes the bug by validating the length of the "filesystem
type" argument passed to get_fs_type() function.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
Suggested-by: Joe Perches <joe@perches.com>
---
Changelog:
v1->v2: Fix commit message.

 fs/filesystems.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/filesystems.c b/fs/filesystems.c
index a920ad2..8e309d3 100644
--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -275,6 +275,9 @@ struct file_system_type *get_fs_type(const char *name)
 	const char *dot = strchr(name, '.');
 	int len = dot ? dot - name : strlen(name);
 
+       if (len >= PATH_MAX)
+               return NULL;
+
 	fs = __get_fs_type(name, len);
 	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
 		fs = __get_fs_type(name, len);
-- 
2.9.4

Re: [PATCH V2] get_fs_type: Validate fs type string argument

[Chandan Rajendra]

On Tuesday, July 11, 2017 7:34:21 PM IST Chandan Rajendra wrote:
> On ppc64, When a non-nul terminated string is passed as an argument to
> the mount(2) syscall, copy_mount_string() ends up allocating 64k (the
> PAGE_SIZE on ppc64) worth of space for holding the string in kernel's
> address space.
> 
> Later, in set_precision() (invoked indirectly by get_fs_type()), we end
> up assigning 65535 as the value to 'struct printf_spec'->precision
> member. This field has a width of 16 bits and also it is signed data
> type. Hence an invalid value ends up getting assigned. This causes the
> "WARN_ONCE(spec->precision != prec, "precision %d too large", prec)"
> statement inside set_precision() to be executed.
> 
> This commit fixes the bug by validating the length of the "filesystem
> type" argument passed to get_fs_type() function.
> 
> Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
> Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com>
> Suggested-by: Joe Perches <joe@perches.com>
> ---
> Changelog:
> v1->v2: Fix commit message.
> 
>  fs/filesystems.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/filesystems.c b/fs/filesystems.c
> index a920ad2..8e309d3 100644
> --- a/fs/filesystems.c
> +++ b/fs/filesystems.c
> @@ -275,6 +275,9 @@ struct file_system_type *get_fs_type(const char *name)
>  	const char *dot = strchr(name, '.');
>  	int len = dot ? dot - name : strlen(name);
> 
> +       if (len >= PATH_MAX)
> +               return NULL;
> +
>  	fs = __get_fs_type(name, len);
>  	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
>  		fs = __get_fs_type(name, len);
> 

Hi Al Viro,

Can you please let me know if you have any review comments about this patch.

-- 
chandan