From 868c1b8431f297ade8deba5baf903f73cf5e11c6 Mon Sep 17 00:00:00 2001 From: Ed Maste Date: Mon, 28 Mar 2022 17:03:10 -0400 Subject: [PATCH] fstyp: detect Raspberry Pi Pico boot filesystem as FAT fstyp looks for a 0x55 0xAA signature at offset 510, but this is not required by specifications and is not proivded by the Raspberry Pi Nano bootloader. We should really remove the signature check and implement a more comprehensive BPB validation instead, but it will require more investigation and testing. For now just add a special case for the Raspberry Pi Nano bootloader, to avoid introducing regressions or new false positives. PR: 262896 Reviewed by: delphij MFC after: 3 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D34699 --- usr.sbin/fstyp/msdosfs.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/usr.sbin/fstyp/msdosfs.c b/usr.sbin/fstyp/msdosfs.c index 47d2383fbc8f..b2144fa46cb1 100644 --- a/usr.sbin/fstyp/msdosfs.c +++ b/usr.sbin/fstyp/msdosfs.c @@ -41,6 +41,24 @@ __FBSDID("$FreeBSD$"); #define LABEL_NO_NAME "NO NAME " +/* + * XXX the signature 0x55 0xAA as the last two bytes of 512 is not required + * by specifications, but was historically required by fstyp. This check + * should be removed, with a more comprehensive BPB validation instead. + */ +static bool +check_signature(uint8_t sector0[512]) +{ + /* Check for the FAT boot sector signature. */ + if (sector0[510] == 0x55 && sector0[511] == 0xaa) + return (true); + /* Special case for Raspberry Pi Nano bootloader. */ + if (sector0[510] == 0 && sector0[511] == 0 && + sector0[0] == 0xeb && sector0[1] == 0x3c && sector0[2] == 0x90) + return (true); + return (false); +} + int fstyp_msdosfs(FILE *fp, char *label, size_t size) { @@ -58,8 +76,7 @@ fstyp_msdosfs(FILE *fp, char *label, size_t size) if (sector0 == NULL) return (1); - /* Check for the FAT boot sector signature. */ - if (sector0[510] != 0x55 || sector0[511] != 0xaa) { + if (!check_signature(sector0)) { goto error; }