From 6e42aec7c75947e0d6b38400628f171364eb8231 Mon Sep 17 00:00:00 2001 From: Matthias Kaehlcke Date: Tue, 6 Sep 2022 18:18:12 -0700 Subject: LoadPin: Require file with verity root digests to have a header LoadPin expects the file with trusted verity root digests to be an ASCII file with one digest (hex value) per line. A pinned root could contain files that meet these format requirements, even though the hex values don't represent trusted root digests. Add a new requirement to the file format which consists in the first line containing a fixed string. This prevents attackers from feeding files with an otherwise valid format to LoadPin. Suggested-by: Sarthak Kukreti Signed-off-by: Matthias Kaehlcke Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220906181725.1.I3f51d1bb0014e5a5951be4ad3c5ad7c7ca1dfc32@changeid --- security/loadpin/Kconfig | 7 ++++++- security/loadpin/loadpin.c | 16 +++++++++++++++- 2 files changed, 21 insertions(+), 2 deletions(-) diff --git a/security/loadpin/Kconfig b/security/loadpin/Kconfig index 994c1d9376e6..6724eaba3d36 100644 --- a/security/loadpin/Kconfig +++ b/security/loadpin/Kconfig @@ -33,4 +33,9 @@ config SECURITY_LOADPIN_VERITY on the LoadPin securityfs entry 'dm-verity'. The ioctl expects a file descriptor of a file with verity digests as parameter. The file must be located on the pinned root and - contain one digest per line. + start with the line: + + # LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS + + This is followed by the verity digests, with one digest per + line. diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c index 44521582dcba..de41621f4998 100644 --- a/security/loadpin/loadpin.c +++ b/security/loadpin/loadpin.c @@ -21,6 +21,8 @@ #include #include +#define VERITY_DIGEST_FILE_HEADER "# LOADPIN_TRUSTED_VERITY_ROOT_DIGESTS" + static void report_load(const char *origin, struct file *file, char *operation) { char *cmdline, *pathname; @@ -292,9 +294,21 @@ static int read_trusted_verity_root_digests(unsigned int fd) p = strim(data); while ((d = strsep(&p, "\n")) != NULL) { - int len = strlen(d); + int len; struct dm_verity_loadpin_trusted_root_digest *trd; + if (d == data) { + /* first line, validate header */ + if (strcmp(d, VERITY_DIGEST_FILE_HEADER)) { + rc = -EPROTO; + goto err; + } + + continue; + } + + len = strlen(d); + if (len % 2) { rc = -EPROTO; goto err; -- cgit