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copy_mount_string: Limit string length to PATH_MAX 

On ppc64le, When a string with PAGE_SIZE - 1 (i.e. 64k-1) length is
passed as a "filesystem type" argument to the mount(2) syscall,
copy_mount_string() ends up allocating 64k (the PAGE_SIZE on ppc64le)
worth of space for holding the string in kernel's address space.

Later, in set_precision() (invoked by get_fs_type() ->
__request_module() -> vsnprintf()), we end up assigning
strlen(fs-type-string) i.e. 65535 as the
value to 'struct printf_spec'->precision member. This field has a width
of 16 bits and it is a 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 limiting the length of the string passed by
copy_mount_string() to strndup_user() to PATH_MAX.

Signed-off-by: Chandan Rajendra <chandan@linux.ibm.com>
Reported-by: Abdul Haleem <abdhalee@linux.ibm.com>
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Chandan Rajendra 2019-01-22 12:21:52 +05:30 committed by Al Viro
parent 35ac118424
commit fbdb440132
1 changed files with 1 additions and 1 deletions
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2
fs/namespace.c
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@ -2746,7 +2746,7 @@ void *copy_mount_options(const void __user * data)
char *copy_mount_string(const void __user *data)
{
return data ? strndup_user(data, PAGE_SIZE) : NULL;
return data ? strndup_user(data, PATH_MAX) : NULL;
}
/*