From fbdb44013202305cd2aefb01df0a92bb55819702 Mon Sep 17 00:00:00 2001 From: Chandan Rajendra Date: Tue, 22 Jan 2019 12:21:52 +0530 Subject: [PATCH] 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 Reported-by: Abdul Haleem Suggested-by: Al Viro Signed-off-by: Al Viro --- fs/namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/namespace.c b/fs/namespace.c index a677b59efd74..c373c769e0ce 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -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; } /*