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blobmsg_format_element() printed the attribute name whenever it formatted an element in a table context (without_name == false), calling blobmsg_name() unconditionally. blobmsg_name() blind-casts the attribute payload to a struct blobmsg_hdr and returns hdr->name, and blobmsg_format_string() then strlen()s that pointer with no length bound. A non-extended attribute carries no blobmsg name header. Such an attribute still passes blobmsg_check_attr(attr, false): the name check returns true for a non-extended attribute when no name is required, and a garbage attribute declaring itself BLOBMSG_TYPE_TABLE or BLOBMSG_TYPE_ARRAY has no entry in blob_type[] and so skips content validation entirely. Its raw bytes are then reinterpreted as a length-prefixed name string and strlen()d past the end of the attribute, leaking adjacent memory into the JSON output. Both ubus (via the monitor path) and rpcd forward attacker-controlled, non-revalidated UBUS_ATTR_DATA to this formatter. Guard the name access with blob_is_extended() so the name is only read from attributes that actually carry a name header. For extended attributes blobmsg_check_attr() has already verified the name is NUL-terminated within bounds, so the subsequent strlen() is safe. Add a regression test that crafts a non-extended, TABLE-typed attribute whose payload ends exactly at the allocation boundary; on an unfixed build the name strlen() reads past it, which the sanitized test catches. Reported-by: Erfan-Nasiri <https://github.com/Erfan-Nasiri> Fixes: 0918243 ("move json formatting to the blobmsg_json library") Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
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blobmsg_format_element() printed the attribute name whenever it formatted an element in a table context (without_name == false), calling blobmsg_name() unconditionally. blobmsg_name() blind-casts the attribute payload to a struct blobmsg_hdr and returns hdr->name, and blobmsg_format_string() then strlen()s that pointer with no length bound.
A non-extended attribute carries no blobmsg name header. Such an attribute still passes blobmsg_check_attr(attr, false): the name check returns true for a non-extended attribute when no name is required, and a garbage attribute declaring itself BLOBMSG_TYPE_TABLE or BLOBMSG_TYPE_ARRAY has no entry in blob_type[] and so skips content validation entirely. Its raw bytes are then reinterpreted as a length-prefixed name string and strlen()d past the end of the attribute, leaking adjacent memory into the JSON output. Both ubus (via the monitor path) and rpcd forward attacker-controlled, non-revalidated UBUS_ATTR_DATA to this formatter.
Guard the name access with blob_is_extended() so the name is only read from attributes that actually carry a name header. For extended attributes blobmsg_check_attr() has already verified the name is NUL-terminated within bounds, so the subsequent strlen() is safe.
Add a regression test that crafts a non-extended, TABLE-typed attribute whose payload ends exactly at the allocation boundary; on an unfixed build the name strlen() reads past it, which the sanitized test catches.
Reported-by: Erfan-Nasiri https://github.com/Erfan-Nasiri
Fixes: 0918243 ("move json formatting to the blobmsg_json library")
Assisted-by: Claude:claude-opus-4-8