From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: Daniel Axtens Date: Mon, 18 Jan 2021 11:46:39 +1100 Subject: [PATCH] fs/fshelp: Catch impermissibly large block sizes in read helper A fuzzed HFS+ filesystem had log2blocksize = 22. This gave log2blocksize + GRUB_DISK_SECTOR_BITS = 31. 1 << 31 = 0x80000000, which is -1 as an int. This caused some wacky behavior later on in the function, leading to out-of-bounds writes on the destination buffer. Catch log2blocksize + GRUB_DISK_SECTOR_BITS >= 31. We could be stricter, but this is the minimum that will prevent integer size weirdness. Signed-off-by: Daniel Axtens Reviewed-by: Daniel Kiper --- grub-core/fs/fshelp.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/grub-core/fs/fshelp.c b/grub-core/fs/fshelp.c index 4c902adf3..a2d0d297a 100644 --- a/grub-core/fs/fshelp.c +++ b/grub-core/fs/fshelp.c @@ -362,6 +362,18 @@ grub_fshelp_read_file (grub_disk_t disk, grub_fshelp_node_t node, grub_disk_addr_t i, blockcnt; int blocksize = 1 << (log2blocksize + GRUB_DISK_SECTOR_BITS); + /* + * Catch blatantly invalid log2blocksize. We could be a lot stricter, but + * this is the most permissive we can be before we start to see integer + * overflow/underflow issues. + */ + if (log2blocksize + GRUB_DISK_SECTOR_BITS >= 31) + { + grub_error (GRUB_ERR_OUT_OF_RANGE, + N_("blocksize too large")); + return -1; + } + if (pos > filesize) { grub_error (GRUB_ERR_OUT_OF_RANGE,