From ad29d0304983e283d4aec4ee5462942eaf5c03ac Mon Sep 17 00:00:00 2001 From: Tobias Schramm Date: Thu, 15 Nov 2018 03:42:48 +0100 Subject: blobmsg: add _len variants for all attribute checking methods MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Introduce _len variants of blobmsg attribute checking functions which aims to provide safer implementation as those functions should limit all memory accesses performed on the blob to the range [attr, attr + len] (upper bound non inclusive) and thus should be suited for checking of untrusted blob attributes. While at it add some comments in order to make it clear. Signed-off-by: Tobias Schramm [_safe -> _len, blobmsg_check_array_len fix, commit subject/desc facelift] Signed-off-by: Petr Štetiar --- blobmsg.c | 21 ++++++++++++++++++--- blobmsg.h | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 72 insertions(+), 4 deletions(-) --- a/blobmsg.c +++ b/blobmsg.c @@ -101,11 +101,21 @@ bool blobmsg_check_attr_len(const struct int blobmsg_check_array(const struct blob_attr *attr, int type) { + return blobmsg_check_array_len(attr, type, blob_raw_len(attr)); +} + +int blobmsg_check_array_len(const struct blob_attr *attr, int type, size_t len) +{ struct blob_attr *cur; bool name; - int rem; int size = 0; + if (type > BLOBMSG_TYPE_LAST) + return -1; + + if (!blobmsg_check_attr_len(attr, false, len)) + return -1; + switch (blobmsg_type(attr)) { case BLOBMSG_TYPE_TABLE: name = true; @@ -117,11 +127,11 @@ int blobmsg_check_array(const struct blo return -1; } - blobmsg_for_each_attr(cur, attr, rem) { + __blobmsg_for_each_attr(cur, attr, len) { if (type != BLOBMSG_TYPE_UNSPEC && blobmsg_type(cur) != type) return -1; - if (!blobmsg_check_attr(cur, name)) + if (!blobmsg_check_attr_len(cur, name, len)) return -1; size++; @@ -135,6 +145,11 @@ bool blobmsg_check_attr_list(const struc return blobmsg_check_array(attr, type) >= 0; } +bool blobmsg_check_attr_list_len(const struct blob_attr *attr, int type, size_t len) +{ + return blobmsg_check_array_len(attr, type, len) >= 0; +} + int blobmsg_parse_array(const struct blobmsg_policy *policy, int policy_len, struct blob_attr **tb, void *data, unsigned int len) { --- a/blobmsg.h +++ b/blobmsg.h @@ -104,19 +104,66 @@ static inline int blobmsg_len(const stru return blobmsg_data_len(attr); } +/* + * blobmsg_check_attr: validate a list of attributes + * + * This method may be used with trusted data only. Providing + * malformed blobs will cause out of bounds memory access. + */ bool blobmsg_check_attr(const struct blob_attr *attr, bool name); -bool blobmsg_check_attr_list(const struct blob_attr *attr, int type); +/* + * blobmsg_check_attr_len: validate a list of attributes + * + * This method should be safer implementation of blobmsg_check_attr. + * It will limit all memory access performed on the blob to the + * range [attr, attr + len] (upper bound non inclusive) and is + * thus suited for checking of untrusted blob attributes. + */ bool blobmsg_check_attr_len(const struct blob_attr *attr, bool name, size_t len); /* + * blobmsg_check_attr_list: validate a list of attributes + * + * This method may be used with trusted data only. Providing + * malformed blobs will cause out of bounds memory access. + */ +bool blobmsg_check_attr_list(const struct blob_attr *attr, int type); + +/* + * blobmsg_check_attr_list_len: validate a list of untrusted attributes + * + * This method should be safer implementation of blobmsg_check_attr_list. + * It will limit all memory access performed on the blob to the + * range [attr, attr + len] (upper bound non inclusive) and is + * thus suited for checking of untrusted blob attributes. + */ +bool blobmsg_check_attr_list_len(const struct blob_attr *attr, int type, size_t len); + +/* * blobmsg_check_array: validate array/table and return size * * Checks if all elements of an array or table are valid and have * the specified type. Returns the number of elements in the array + * + * This method may be used with trusted data only. Providing + * malformed blobs will cause out of bounds memory access. */ int blobmsg_check_array(const struct blob_attr *attr, int type); +/* + * blobmsg_check_array_len: validate untrusted array/table and return size + * + * Checks if all elements of an array or table are valid and have + * the specified type. Returns the number of elements in the array. + * + * This method should be safer implementation of blobmsg_check_array. + * It will limit all memory access performed on the blob to the + * range [attr, attr + len] (upper bound non inclusive) and is + * thus suited for checking of untrusted blob attributes. + */ +int blobmsg_check_array_len(const struct blob_attr *attr, int type, size_t len); + int blobmsg_parse(const struct blobmsg_policy *policy, int policy_len, struct blob_attr **tb, void *data, unsigned int len); int blobmsg_parse_array(const struct blobmsg_policy *policy, int policy_len, @@ -271,5 +318,11 @@ int blobmsg_printf(struct blob_buf *buf, rem >= sizeof(struct blob_attr) && (blob_pad_len(pos) <= rem) && \ (blob_pad_len(pos) >= sizeof(struct blob_attr)); \ rem -= blob_pad_len(pos), pos = blob_next(pos)) + +#define __blobmsg_for_each_attr(pos, attr, rem) \ + for (pos = (struct blob_attr *) (attr ? blobmsg_data(attr) : NULL); \ + rem >= sizeof(struct blob_attr) && (blob_pad_len(pos) <= rem) && \ + (blob_pad_len(pos) >= sizeof(struct blob_attr)); \ + rem -= blob_pad_len(pos), pos = blob_next(pos)) #endif